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//===- InstructionCombining.cpp - Combine multiple instructions -----------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// InstructionCombining - Combine instructions to form fewer, simple
// instructions. This pass does not modify the CFG. This pass is where
// algebraic simplification happens.
//
// This pass combines things like:
// %Y = add i32 %X, 1
// %Z = add i32 %Y, 1
// into:
// %Z = add i32 %X, 2
//
// This is a simple worklist driven algorithm.
//
// This pass guarantees that the following canonicalizations are performed on
// the program:
// 1. If a binary operator has a constant operand, it is moved to the RHS
// 2. Bitwise operators with constant operands are always grouped so that
// shifts are performed first, then or's, then and's, then xor's.
// 3. Compare instructions are converted from <,>,<=,>= to ==,!= if possible
// 4. All cmp instructions on boolean values are replaced with logical ops
// 5. add X, X is represented as (X*2) => (X << 1)
// 6. Multiplies with a power-of-two constant argument are transformed into
// shifts.
// ... etc.
//
//===----------------------------------------------------------------------===//
#include "InstCombineInternal.h"
#include "llvm-c/Initialization.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/BasicAliasAnalysis.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/EHPersonalities.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/InstCombine/InstCombine.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
#include <algorithm>
#include <climits>
using namespace llvm;
using namespace llvm::PatternMatch;
#define DEBUG_TYPE "instcombine"
STATISTIC(NumCombined , "Number of insts combined");
STATISTIC(NumConstProp, "Number of constant folds");
STATISTIC(NumDeadInst , "Number of dead inst eliminated");
STATISTIC(NumSunkInst , "Number of instructions sunk");
STATISTIC(NumExpand, "Number of expansions");
STATISTIC(NumFactor , "Number of factorizations");
STATISTIC(NumReassoc , "Number of reassociations");
static cl::opt<bool>
EnableExpensiveCombines("expensive-combines",
cl::desc("Enable expensive instruction combines"));
static cl::opt<unsigned>
MaxArraySize("instcombine-maxarray-size", cl::init(1024),
cl::desc("Maximum array size considered when doing a combine"));
Value *InstCombiner::EmitGEPOffset(User *GEP) {
return llvm::EmitGEPOffset(Builder, DL, GEP);
}
/// Return true if it is desirable to convert an integer computation from a
/// given bit width to a new bit width.
/// We don't want to convert from a legal to an illegal type or from a smaller
/// to a larger illegal type. A width of '1' is always treated as a legal type
/// because i1 is a fundamental type in IR, and there are many specialized
/// optimizations for i1 types.
bool InstCombiner::shouldChangeType(unsigned FromWidth,
unsigned ToWidth) const {
bool FromLegal = FromWidth == 1 || DL.isLegalInteger(FromWidth);
bool ToLegal = ToWidth == 1 || DL.isLegalInteger(ToWidth);
// If this is a legal integer from type, and the result would be an illegal
// type, don't do the transformation.
if (FromLegal && !ToLegal)
return false;
// Otherwise, if both are illegal, do not increase the size of the result. We
// do allow things like i160 -> i64, but not i64 -> i160.
if (!FromLegal && !ToLegal && ToWidth > FromWidth)
return false;
return true;
}
/// Return true if it is desirable to convert a computation from 'From' to 'To'.
/// We don't want to convert from a legal to an illegal type or from a smaller
/// to a larger illegal type. i1 is always treated as a legal type because it is
/// a fundamental type in IR, and there are many specialized optimizations for
/// i1 types.
bool InstCombiner::shouldChangeType(Type *From, Type *To) const {
assert(From->isIntegerTy() && To->isIntegerTy());
unsigned FromWidth = From->getPrimitiveSizeInBits();
unsigned ToWidth = To->getPrimitiveSizeInBits();
return shouldChangeType(FromWidth, ToWidth);
}
// Return true, if No Signed Wrap should be maintained for I.
// The No Signed Wrap flag can be kept if the operation "B (I.getOpcode) C",
// where both B and C should be ConstantInts, results in a constant that does
// not overflow. This function only handles the Add and Sub opcodes. For
// all other opcodes, the function conservatively returns false.
static bool MaintainNoSignedWrap(BinaryOperator &I, Value *B, Value *C) {
OverflowingBinaryOperator *OBO = dyn_cast<OverflowingBinaryOperator>(&I);
if (!OBO || !OBO->hasNoSignedWrap())
return false;
// We reason about Add and Sub Only.
Instruction::BinaryOps Opcode = I.getOpcode();
if (Opcode != Instruction::Add && Opcode != Instruction::Sub)
return false;
const APInt *BVal, *CVal;
if (!match(B, m_APInt(BVal)) || !match(C, m_APInt(CVal)))
return false;
bool Overflow = false;
if (Opcode == Instruction::Add)
(void)BVal->sadd_ov(*CVal, Overflow);
else
(void)BVal->ssub_ov(*CVal, Overflow);
return !Overflow;
}
/// Conservatively clears subclassOptionalData after a reassociation or
/// commutation. We preserve fast-math flags when applicable as they can be
/// preserved.
static void ClearSubclassDataAfterReassociation(BinaryOperator &I) {
FPMathOperator *FPMO = dyn_cast<FPMathOperator>(&I);
if (!FPMO) {
I.clearSubclassOptionalData();
return;
}
FastMathFlags FMF = I.getFastMathFlags();
I.clearSubclassOptionalData();
I.setFastMathFlags(FMF);
}
/// Combine constant operands of associative operations either before or after a
/// cast to eliminate one of the associative operations:
/// (op (cast (op X, C2)), C1) --> (cast (op X, op (C1, C2)))
/// (op (cast (op X, C2)), C1) --> (op (cast X), op (C1, C2))
static bool simplifyAssocCastAssoc(BinaryOperator *BinOp1) {
auto *Cast = dyn_cast<CastInst>(BinOp1->getOperand(0));
if (!Cast || !Cast->hasOneUse())
return false;
// TODO: Enhance logic for other casts and remove this check.
auto CastOpcode = Cast->getOpcode();
if (CastOpcode != Instruction::ZExt)
return false;
// TODO: Enhance logic for other BinOps and remove this check.
if (!BinOp1->isBitwiseLogicOp())
return false;
auto AssocOpcode = BinOp1->getOpcode();
auto *BinOp2 = dyn_cast<BinaryOperator>(Cast->getOperand(0));
if (!BinOp2 || !BinOp2->hasOneUse() || BinOp2->getOpcode() != AssocOpcode)
return false;
Constant *C1, *C2;
if (!match(BinOp1->getOperand(1), m_Constant(C1)) ||
!match(BinOp2->getOperand(1), m_Constant(C2)))
return false;
// TODO: This assumes a zext cast.
// Eg, if it was a trunc, we'd cast C1 to the source type because casting C2
// to the destination type might lose bits.
// Fold the constants together in the destination type:
// (op (cast (op X, C2)), C1) --> (op (cast X), FoldedC)
Type *DestTy = C1->getType();
Constant *CastC2 = ConstantExpr::getCast(CastOpcode, C2, DestTy);
Constant *FoldedC = ConstantExpr::get(AssocOpcode, C1, CastC2);
Cast->setOperand(0, BinOp2->getOperand(0));
BinOp1->setOperand(1, FoldedC);
return true;
}
/// This performs a few simplifications for operators that are associative or
/// commutative:
///
/// Commutative operators:
///
/// 1. Order operands such that they are listed from right (least complex) to
/// left (most complex). This puts constants before unary operators before
/// binary operators.
///
/// Associative operators:
///
/// 2. Transform: "(A op B) op C" ==> "A op (B op C)" if "B op C" simplifies.
/// 3. Transform: "A op (B op C)" ==> "(A op B) op C" if "A op B" simplifies.
///
/// Associative and commutative operators:
///
/// 4. Transform: "(A op B) op C" ==> "(C op A) op B" if "C op A" simplifies.
/// 5. Transform: "A op (B op C)" ==> "B op (C op A)" if "C op A" simplifies.
/// 6. Transform: "(A op C1) op (B op C2)" ==> "(A op B) op (C1 op C2)"
/// if C1 and C2 are constants.
bool InstCombiner::SimplifyAssociativeOrCommutative(BinaryOperator &I) {
Instruction::BinaryOps Opcode = I.getOpcode();
bool Changed = false;
do {
// Order operands such that they are listed from right (least complex) to
// left (most complex). This puts constants before unary operators before
// binary operators.
if (I.isCommutative() && getComplexity(I.getOperand(0)) <
getComplexity(I.getOperand(1)))
Changed = !I.swapOperands();
BinaryOperator *Op0 = dyn_cast<BinaryOperator>(I.getOperand(0));
BinaryOperator *Op1 = dyn_cast<BinaryOperator>(I.getOperand(1));
if (I.isAssociative()) {
// Transform: "(A op B) op C" ==> "A op (B op C)" if "B op C" simplifies.
if (Op0 && Op0->getOpcode() == Opcode) {
Value *A = Op0->getOperand(0);
Value *B = Op0->getOperand(1);
Value *C = I.getOperand(1);
// Does "B op C" simplify?
if (Value *V = SimplifyBinOp(Opcode, B, C, SQ)) {
// It simplifies to V. Form "A op V".
I.setOperand(0, A);
I.setOperand(1, V);
// Conservatively clear the optional flags, since they may not be
// preserved by the reassociation.
if (MaintainNoSignedWrap(I, B, C) &&
(!Op0 || (isa<BinaryOperator>(Op0) && Op0->hasNoSignedWrap()))) {
// Note: this is only valid because SimplifyBinOp doesn't look at
// the operands to Op0.
I.clearSubclassOptionalData();
I.setHasNoSignedWrap(true);
} else {
ClearSubclassDataAfterReassociation(I);
}
Changed = true;
++NumReassoc;
continue;
}
}
// Transform: "A op (B op C)" ==> "(A op B) op C" if "A op B" simplifies.
if (Op1 && Op1->getOpcode() == Opcode) {
Value *A = I.getOperand(0);
Value *B = Op1->getOperand(0);
Value *C = Op1->getOperand(1);
// Does "A op B" simplify?
if (Value *V = SimplifyBinOp(Opcode, A, B, SQ)) {
// It simplifies to V. Form "V op C".
I.setOperand(0, V);
I.setOperand(1, C);
// Conservatively clear the optional flags, since they may not be
// preserved by the reassociation.
ClearSubclassDataAfterReassociation(I);
Changed = true;
++NumReassoc;
continue;
}
}
}
if (I.isAssociative() && I.isCommutative()) {
if (simplifyAssocCastAssoc(&I)) {
Changed = true;
++NumReassoc;
continue;
}
// Transform: "(A op B) op C" ==> "(C op A) op B" if "C op A" simplifies.
if (Op0 && Op0->getOpcode() == Opcode) {
Value *A = Op0->getOperand(0);
Value *B = Op0->getOperand(1);
Value *C = I.getOperand(1);
// Does "C op A" simplify?
if (Value *V = SimplifyBinOp(Opcode, C, A, SQ)) {
// It simplifies to V. Form "V op B".
I.setOperand(0, V);
I.setOperand(1, B);
// Conservatively clear the optional flags, since they may not be
// preserved by the reassociation.
ClearSubclassDataAfterReassociation(I);
Changed = true;
++NumReassoc;
continue;
}
}
// Transform: "A op (B op C)" ==> "B op (C op A)" if "C op A" simplifies.
if (Op1 && Op1->getOpcode() == Opcode) {
Value *A = I.getOperand(0);
Value *B = Op1->getOperand(0);
Value *C = Op1->getOperand(1);
// Does "C op A" simplify?
if (Value *V = SimplifyBinOp(Opcode, C, A, SQ)) {
// It simplifies to V. Form "B op V".
I.setOperand(0, B);
I.setOperand(1, V);
// Conservatively clear the optional flags, since they may not be
// preserved by the reassociation.
ClearSubclassDataAfterReassociation(I);
Changed = true;
++NumReassoc;
continue;
}
}
// Transform: "(A op C1) op (B op C2)" ==> "(A op B) op (C1 op C2)"
// if C1 and C2 are constants.
if (Op0 && Op1 &&
Op0->getOpcode() == Opcode && Op1->getOpcode() == Opcode &&
isa<Constant>(Op0->getOperand(1)) &&
isa<Constant>(Op1->getOperand(1)) &&
Op0->hasOneUse() && Op1->hasOneUse()) {
Value *A = Op0->getOperand(0);
Constant *C1 = cast<Constant>(Op0->getOperand(1));
Value *B = Op1->getOperand(0);
Constant *C2 = cast<Constant>(Op1->getOperand(1));
Constant *Folded = ConstantExpr::get(Opcode, C1, C2);
BinaryOperator *New = BinaryOperator::Create(Opcode, A, B);
if (isa<FPMathOperator>(New)) {
FastMathFlags Flags = I.getFastMathFlags();
Flags &= Op0->getFastMathFlags();
Flags &= Op1->getFastMathFlags();
New->setFastMathFlags(Flags);
}
InsertNewInstWith(New, I);
New->takeName(Op1);
I.setOperand(0, New);
I.setOperand(1, Folded);
// Conservatively clear the optional flags, since they may not be
// preserved by the reassociation.
ClearSubclassDataAfterReassociation(I);
Changed = true;
continue;
}
}
// No further simplifications.
return Changed;
} while (1);
}
/// Return whether "X LOp (Y ROp Z)" is always equal to
/// "(X LOp Y) ROp (X LOp Z)".
static bool LeftDistributesOverRight(Instruction::BinaryOps LOp,
Instruction::BinaryOps ROp) {
switch (LOp) {
default:
return false;
case Instruction::And:
// And distributes over Or and Xor.
switch (ROp) {
default:
return false;
case Instruction::Or:
case Instruction::Xor:
return true;
}
case Instruction::Mul:
// Multiplication distributes over addition and subtraction.
switch (ROp) {
default:
return false;
case Instruction::Add:
case Instruction::Sub:
return true;
}
case Instruction::Or:
// Or distributes over And.
switch (ROp) {
default:
return false;
case Instruction::And:
return true;
}
}
}
/// Return whether "(X LOp Y) ROp Z" is always equal to
/// "(X ROp Z) LOp (Y ROp Z)".
static bool RightDistributesOverLeft(Instruction::BinaryOps LOp,
Instruction::BinaryOps ROp) {
if (Instruction::isCommutative(ROp))
return LeftDistributesOverRight(ROp, LOp);
switch (LOp) {
default:
return false;
// (X >> Z) & (Y >> Z) -> (X&Y) >> Z for all shifts.
// (X >> Z) | (Y >> Z) -> (X|Y) >> Z for all shifts.
// (X >> Z) ^ (Y >> Z) -> (X^Y) >> Z for all shifts.
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
switch (ROp) {
default:
return false;
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
return true;
}
}
// TODO: It would be nice to handle division, aka "(X + Y)/Z = X/Z + Y/Z",
// but this requires knowing that the addition does not overflow and other
// such subtleties.
return false;
}
/// This function returns identity value for given opcode, which can be used to
/// factor patterns like (X * 2) + X ==> (X * 2) + (X * 1) ==> X * (2 + 1).
static Value *getIdentityValue(Instruction::BinaryOps Opcode, Value *V) {
if (isa<Constant>(V))
return nullptr;
return ConstantExpr::getBinOpIdentity(Opcode, V->getType());
}
/// This function factors binary ops which can be combined using distributive
/// laws. This function tries to transform 'Op' based TopLevelOpcode to enable
/// factorization e.g for ADD(SHL(X , 2), MUL(X, 5)), When this function called
/// with TopLevelOpcode == Instruction::Add and Op = SHL(X, 2), transforms
/// SHL(X, 2) to MUL(X, 4) i.e. returns Instruction::Mul with LHS set to 'X' and
/// RHS to 4.
static Instruction::BinaryOps
getBinOpsForFactorization(Instruction::BinaryOps TopLevelOpcode,
BinaryOperator *Op, Value *&LHS, Value *&RHS) {
assert(Op && "Expected a binary operator");
LHS = Op->getOperand(0);
RHS = Op->getOperand(1);
switch (TopLevelOpcode) {
default:
return Op->getOpcode();
case Instruction::Add:
case Instruction::Sub:
if (Op->getOpcode() == Instruction::Shl) {
if (Constant *CST = dyn_cast<Constant>(Op->getOperand(1))) {
// The multiplier is really 1 << CST.
RHS = ConstantExpr::getShl(ConstantInt::get(Op->getType(), 1), CST);
return Instruction::Mul;
}
}
return Op->getOpcode();
}
// TODO: We can add other conversions e.g. shr => div etc.
}
/// This tries to simplify binary operations by factorizing out common terms
/// (e. g. "(A*B)+(A*C)" -> "A*(B+C)").
Value *InstCombiner::tryFactorization(InstCombiner::BuilderTy *Builder,
BinaryOperator &I,
Instruction::BinaryOps InnerOpcode,
Value *A, Value *B, Value *C, Value *D) {
assert(A && B && C && D && "All values must be provided");
Value *V = nullptr;
Value *SimplifiedInst = nullptr;
Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
Instruction::BinaryOps TopLevelOpcode = I.getOpcode();
// Does "X op' Y" always equal "Y op' X"?
bool InnerCommutative = Instruction::isCommutative(InnerOpcode);
// Does "X op' (Y op Z)" always equal "(X op' Y) op (X op' Z)"?
if (LeftDistributesOverRight(InnerOpcode, TopLevelOpcode))
// Does the instruction have the form "(A op' B) op (A op' D)" or, in the
// commutative case, "(A op' B) op (C op' A)"?
if (A == C || (InnerCommutative && A == D)) {
if (A != C)
std::swap(C, D);
// Consider forming "A op' (B op D)".
// If "B op D" simplifies then it can be formed with no cost.
V = SimplifyBinOp(TopLevelOpcode, B, D, SQ);
// If "B op D" doesn't simplify then only go on if both of the existing
// operations "A op' B" and "C op' D" will be zapped as no longer used.
if (!V && LHS->hasOneUse() && RHS->hasOneUse())
V = Builder->CreateBinOp(TopLevelOpcode, B, D, RHS->getName());
if (V) {
SimplifiedInst = Builder->CreateBinOp(InnerOpcode, A, V);
}
}
// Does "(X op Y) op' Z" always equal "(X op' Z) op (Y op' Z)"?
if (!SimplifiedInst && RightDistributesOverLeft(TopLevelOpcode, InnerOpcode))
// Does the instruction have the form "(A op' B) op (C op' B)" or, in the
// commutative case, "(A op' B) op (B op' D)"?
if (B == D || (InnerCommutative && B == C)) {
if (B != D)
std::swap(C, D);
// Consider forming "(A op C) op' B".
// If "A op C" simplifies then it can be formed with no cost.
V = SimplifyBinOp(TopLevelOpcode, A, C, SQ);
// If "A op C" doesn't simplify then only go on if both of the existing
// operations "A op' B" and "C op' D" will be zapped as no longer used.
if (!V && LHS->hasOneUse() && RHS->hasOneUse())
V = Builder->CreateBinOp(TopLevelOpcode, A, C, LHS->getName());
if (V) {
SimplifiedInst = Builder->CreateBinOp(InnerOpcode, V, B);
}
}
if (SimplifiedInst) {
++NumFactor;
SimplifiedInst->takeName(&I);
// Check if we can add NSW flag to SimplifiedInst. If so, set NSW flag.
// TODO: Check for NUW.
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(SimplifiedInst)) {
if (isa<OverflowingBinaryOperator>(SimplifiedInst)) {
bool HasNSW = false;
if (isa<OverflowingBinaryOperator>(&I))
HasNSW = I.hasNoSignedWrap();
if (auto *LOBO = dyn_cast<OverflowingBinaryOperator>(LHS))
HasNSW &= LOBO->hasNoSignedWrap();
if (auto *ROBO = dyn_cast<OverflowingBinaryOperator>(RHS))
HasNSW &= ROBO->hasNoSignedWrap();
// We can propagate 'nsw' if we know that
// %Y = mul nsw i16 %X, C
// %Z = add nsw i16 %Y, %X
// =>
// %Z = mul nsw i16 %X, C+1
//
// iff C+1 isn't INT_MIN
const APInt *CInt;
if (TopLevelOpcode == Instruction::Add &&
InnerOpcode == Instruction::Mul)
if (match(V, m_APInt(CInt)) && !CInt->isMinSignedValue())
BO->setHasNoSignedWrap(HasNSW);
}
}
}
return SimplifiedInst;
}
/// This tries to simplify binary operations which some other binary operation
/// distributes over either by factorizing out common terms
/// (eg "(A*B)+(A*C)" -> "A*(B+C)") or expanding out if this results in
/// simplifications (eg: "A & (B | C) -> (A&B) | (A&C)" if this is a win).
/// Returns the simplified value, or null if it didn't simplify.
Value *InstCombiner::SimplifyUsingDistributiveLaws(BinaryOperator &I) {
Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
BinaryOperator *Op0 = dyn_cast<BinaryOperator>(LHS);
BinaryOperator *Op1 = dyn_cast<BinaryOperator>(RHS);
Instruction::BinaryOps TopLevelOpcode = I.getOpcode();
{
// Factorization.
Value *A, *B, *C, *D;
Instruction::BinaryOps LHSOpcode, RHSOpcode;
if (Op0)
LHSOpcode = getBinOpsForFactorization(TopLevelOpcode, Op0, A, B);
if (Op1)
RHSOpcode = getBinOpsForFactorization(TopLevelOpcode, Op1, C, D);
// The instruction has the form "(A op' B) op (C op' D)". Try to factorize
// a common term.
if (Op0 && Op1 && LHSOpcode == RHSOpcode)
if (Value *V = tryFactorization(Builder, I, LHSOpcode, A, B, C, D))
return V;
// The instruction has the form "(A op' B) op (C)". Try to factorize common
// term.
if (Op0)
if (Value *Ident = getIdentityValue(LHSOpcode, RHS))
if (Value *V =
tryFactorization(Builder, I, LHSOpcode, A, B, RHS, Ident))
return V;
// The instruction has the form "(B) op (C op' D)". Try to factorize common
// term.
if (Op1)
if (Value *Ident = getIdentityValue(RHSOpcode, LHS))
if (Value *V =
tryFactorization(Builder, I, RHSOpcode, LHS, Ident, C, D))
return V;
}
// Expansion.
if (Op0 && RightDistributesOverLeft(Op0->getOpcode(), TopLevelOpcode)) {
// The instruction has the form "(A op' B) op C". See if expanding it out
// to "(A op C) op' (B op C)" results in simplifications.
Value *A = Op0->getOperand(0), *B = Op0->getOperand(1), *C = RHS;
Instruction::BinaryOps InnerOpcode = Op0->getOpcode(); // op'
// Do "A op C" and "B op C" both simplify?
if (Value *L = SimplifyBinOp(TopLevelOpcode, A, C, SQ))
if (Value *R = SimplifyBinOp(TopLevelOpcode, B, C, SQ)) {
// They do! Return "L op' R".
++NumExpand;
C = Builder->CreateBinOp(InnerOpcode, L, R);
C->takeName(&I);
return C;
}
}
if (Op1 && LeftDistributesOverRight(TopLevelOpcode, Op1->getOpcode())) {
// The instruction has the form "A op (B op' C)". See if expanding it out
// to "(A op B) op' (A op C)" results in simplifications.
Value *A = LHS, *B = Op1->getOperand(0), *C = Op1->getOperand(1);
Instruction::BinaryOps InnerOpcode = Op1->getOpcode(); // op'
// Do "A op B" and "A op C" both simplify?
if (Value *L = SimplifyBinOp(TopLevelOpcode, A, B, SQ))
if (Value *R = SimplifyBinOp(TopLevelOpcode, A, C, SQ)) {
// They do! Return "L op' R".
++NumExpand;
A = Builder->CreateBinOp(InnerOpcode, L, R);
A->takeName(&I);
return A;
}
}
// (op (select (a, c, b)), (select (a, d, b))) -> (select (a, (op c, d), 0))
// (op (select (a, b, c)), (select (a, b, d))) -> (select (a, 0, (op c, d)))
if (auto *SI0 = dyn_cast<SelectInst>(LHS)) {
if (auto *SI1 = dyn_cast<SelectInst>(RHS)) {
if (SI0->getCondition() == SI1->getCondition()) {
Value *SI = nullptr;
if (Value *V = SimplifyBinOp(TopLevelOpcode, SI0->getFalseValue(),
SI1->getFalseValue(), SQ))
SI = Builder->CreateSelect(SI0->getCondition(),
Builder->CreateBinOp(TopLevelOpcode,
SI0->getTrueValue(),
SI1->getTrueValue()),
V);
if (Value *V = SimplifyBinOp(TopLevelOpcode, SI0->getTrueValue(),
SI1->getTrueValue(), SQ))
SI = Builder->CreateSelect(
SI0->getCondition(), V,
Builder->CreateBinOp(TopLevelOpcode, SI0->getFalseValue(),
SI1->getFalseValue()));
if (SI) {
SI->takeName(&I);
return SI;
}
}
}
}
return nullptr;
}
/// Given a 'sub' instruction, return the RHS of the instruction if the LHS is a
/// constant zero (which is the 'negate' form).
Value *InstCombiner::dyn_castNegVal(Value *V) const {
if (BinaryOperator::isNeg(V))
return BinaryOperator::getNegArgument(V);
// Constants can be considered to be negated values if they can be folded.
if (ConstantInt *C = dyn_cast<ConstantInt>(V))
return ConstantExpr::getNeg(C);
if (ConstantDataVector *C = dyn_cast<ConstantDataVector>(V))
if (C->getType()->getElementType()->isIntegerTy())
return ConstantExpr::getNeg(C);
if (ConstantVector *CV = dyn_cast<ConstantVector>(V)) {
for (unsigned i = 0, e = CV->getNumOperands(); i != e; ++i) {
Constant *Elt = CV->getAggregateElement(i);
if (!Elt)
return nullptr;
if (isa<UndefValue>(Elt))
continue;
if (!isa<ConstantInt>(Elt))
return nullptr;
}
return ConstantExpr::getNeg(CV);
}
return nullptr;
}
/// Given a 'fsub' instruction, return the RHS of the instruction if the LHS is
/// a constant negative zero (which is the 'negate' form).
Value *InstCombiner::dyn_castFNegVal(Value *V, bool IgnoreZeroSign) const {
if (BinaryOperator::isFNeg(V, IgnoreZeroSign))
return BinaryOperator::getFNegArgument(V);
// Constants can be considered to be negated values if they can be folded.
if (ConstantFP *C = dyn_cast<ConstantFP>(V))
return ConstantExpr::getFNeg(C);
if (ConstantDataVector *C = dyn_cast<ConstantDataVector>(V))
if (C->getType()->getElementType()->isFloatingPointTy())
return ConstantExpr::getFNeg(C);
return nullptr;
}
static Value *foldOperationIntoSelectOperand(Instruction &I, Value *SO,
InstCombiner *IC) {
if (auto *Cast = dyn_cast<CastInst>(&I))
return IC->Builder->CreateCast(Cast->getOpcode(), SO, I.getType());
assert(I.isBinaryOp() && "Unexpected opcode for select folding");
// Figure out if the constant is the left or the right argument.
bool ConstIsRHS = isa<Constant>(I.getOperand(1));
Constant *ConstOperand = cast<Constant>(I.getOperand(ConstIsRHS));
if (auto *SOC = dyn_cast<Constant>(SO)) {
if (ConstIsRHS)
return ConstantExpr::get(I.getOpcode(), SOC, ConstOperand);
return ConstantExpr::get(I.getOpcode(), ConstOperand, SOC);
}
Value *Op0 = SO, *Op1 = ConstOperand;
if (!ConstIsRHS)
std::swap(Op0, Op1);
auto *BO = cast<BinaryOperator>(&I);
Value *RI = IC->Builder->CreateBinOp(BO->getOpcode(), Op0, Op1,
SO->getName() + ".op");
auto *FPInst = dyn_cast<Instruction>(RI);
if (FPInst && isa<FPMathOperator>(FPInst))
FPInst->copyFastMathFlags(BO);
return RI;
}
Instruction *InstCombiner::FoldOpIntoSelect(Instruction &Op, SelectInst *SI) {
// Don't modify shared select instructions.
if (!SI->hasOneUse())
return nullptr;
Value *TV = SI->getTrueValue();
Value *FV = SI->getFalseValue();
if (!(isa<Constant>(TV) || isa<Constant>(FV)))
return nullptr;
// Bool selects with constant operands can be folded to logical ops.
if (SI->getType()->getScalarType()->isIntegerTy(1))
return nullptr;
// If it's a bitcast involving vectors, make sure it has the same number of
// elements on both sides.
if (auto *BC = dyn_cast<BitCastInst>(&Op)) {
VectorType *DestTy = dyn_cast<VectorType>(BC->getDestTy());
VectorType *SrcTy = dyn_cast<VectorType>(BC->getSrcTy());
// Verify that either both or neither are vectors.
if ((SrcTy == nullptr) != (DestTy == nullptr))
return nullptr;
// If vectors, verify that they have the same number of elements.
if (SrcTy && SrcTy->getNumElements() != DestTy->getNumElements())
return nullptr;
}
// Test if a CmpInst instruction is used exclusively by a select as
// part of a minimum or maximum operation. If so, refrain from doing
// any other folding. This helps out other analyses which understand
// non-obfuscated minimum and maximum idioms, such as ScalarEvolution
// and CodeGen. And in this case, at least one of the comparison
// operands has at least one user besides the compare (the select),
// which would often largely negate the benefit of folding anyway.
if (auto *CI = dyn_cast<CmpInst>(SI->getCondition())) {
if (CI->hasOneUse()) {
Value *Op0 = CI->getOperand(0), *Op1 = CI->getOperand(1);
if ((SI->getOperand(1) == Op0 && SI->getOperand(2) == Op1) ||
(SI->getOperand(2) == Op0 && SI->getOperand(1) == Op1))
return nullptr;
}
}
Value *NewTV = foldOperationIntoSelectOperand(Op, TV, this);
Value *NewFV = foldOperationIntoSelectOperand(Op, FV, this);
return SelectInst::Create(SI->getCondition(), NewTV, NewFV, "", nullptr, SI);
}
static Value *foldOperationIntoPhiValue(BinaryOperator *I, Value *InV,
InstCombiner *IC) {
bool ConstIsRHS = isa<Constant>(I->getOperand(1));
Constant *C = cast<Constant>(I->getOperand(ConstIsRHS));
if (auto *InC = dyn_cast<Constant>(InV)) {
if (ConstIsRHS)
return ConstantExpr::get(I->getOpcode(), InC, C);
return ConstantExpr::get(I->getOpcode(), C, InC);
}
Value *Op0 = InV, *Op1 = C;
if (!ConstIsRHS)
std::swap(Op0, Op1);
Value *RI = IC->Builder->CreateBinOp(I->getOpcode(), Op0, Op1, "phitmp");
auto *FPInst = dyn_cast<Instruction>(RI);
if (FPInst && isa<FPMathOperator>(FPInst))
FPInst->copyFastMathFlags(I);
return RI;
}
Instruction *InstCombiner::foldOpIntoPhi(Instruction &I, PHINode *PN) {
unsigned NumPHIValues = PN->getNumIncomingValues();
if (NumPHIValues == 0)
return nullptr;
// We normally only transform phis with a single use. However, if a PHI has
// multiple uses and they are all the same operation, we can fold *all* of the
// uses into the PHI.
if (!PN->hasOneUse()) {
// Walk the use list for the instruction, comparing them to I.
for (User *U : PN->users()) {
Instruction *UI = cast<Instruction>(U);
if (UI != &I && !I.isIdenticalTo(UI))
return nullptr;
}
// Otherwise, we can replace *all* users with the new PHI we form.
}
// Check to see if all of the operands of the PHI are simple constants
// (constantint/constantfp/undef). If there is one non-constant value,
// remember the BB it is in. If there is more than one or if *it* is a PHI,
// bail out. We don't do arbitrary constant expressions here because moving
// their computation can be expensive without a cost model.
BasicBlock *NonConstBB = nullptr;
for (unsigned i = 0; i != NumPHIValues; ++i) {
Value *InVal = PN->getIncomingValue(i);
if (isa<Constant>(InVal) && !isa<ConstantExpr>(InVal))
continue;
if (isa<PHINode>(InVal)) return nullptr; // Itself a phi.
if (NonConstBB) return nullptr; // More than one non-const value.
NonConstBB = PN->getIncomingBlock(i);
// If the InVal is an invoke at the end of the pred block, then we can't
// insert a computation after it without breaking the edge.
if (InvokeInst *II = dyn_cast<InvokeInst>(InVal))
if (II->getParent() == NonConstBB)
return nullptr;
// If the incoming non-constant value is in I's block, we will remove one
// instruction, but insert another equivalent one, leading to infinite
// instcombine.
if (isPotentiallyReachable(I.getParent(), NonConstBB, &DT, LI))
return nullptr;
}
// If there is exactly one non-constant value, we can insert a copy of the
// operation in that block. However, if this is a critical edge, we would be
// inserting the computation on some other paths (e.g. inside a loop). Only
// do this if the pred block is unconditionally branching into the phi block.
if (NonConstBB != nullptr) {
BranchInst *BI = dyn_cast<BranchInst>(NonConstBB->getTerminator());
if (!BI || !BI->isUnconditional()) return nullptr;
}
// Okay, we can do the transformation: create the new PHI node.
PHINode *NewPN = PHINode::Create(I.getType(), PN->getNumIncomingValues());
InsertNewInstBefore(NewPN, *PN);
NewPN->takeName(PN);
// If we are going to have to insert a new computation, do so right before the
// predecessor's terminator.
if (NonConstBB)
Builder->SetInsertPoint(NonConstBB->getTerminator());
// Next, add all of the operands to the PHI.
if (SelectInst *SI = dyn_cast<SelectInst>(&I)) {
// We only currently try to fold the condition of a select when it is a phi,
// not the true/false values.
Value *TrueV = SI->getTrueValue();
Value *FalseV = SI->getFalseValue();
BasicBlock *PhiTransBB = PN->getParent();
for (unsigned i = 0; i != NumPHIValues; ++i) {
BasicBlock *ThisBB = PN->getIncomingBlock(i);
Value *TrueVInPred = TrueV->DoPHITranslation(PhiTransBB, ThisBB);
Value *FalseVInPred = FalseV->DoPHITranslation(PhiTransBB, ThisBB);
Value *InV = nullptr;
// Beware of ConstantExpr: it may eventually evaluate to getNullValue,
// even if currently isNullValue gives false.
Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i));
// For vector constants, we cannot use isNullValue to fold into
// FalseVInPred versus TrueVInPred. When we have individual nonzero
// elements in the vector, we will incorrectly fold InC to
// `TrueVInPred`.
if (InC && !isa<ConstantExpr>(InC) && isa<ConstantInt>(InC))
InV = InC->isNullValue() ? FalseVInPred : TrueVInPred;
else
InV = Builder->CreateSelect(PN->getIncomingValue(i),
TrueVInPred, FalseVInPred, "phitmp");
NewPN->addIncoming(InV, ThisBB);
}
} else if (CmpInst *CI = dyn_cast<CmpInst>(&I)) {
Constant *C = cast<Constant>(I.getOperand(1));
for (unsigned i = 0; i != NumPHIValues; ++i) {
Value *InV = nullptr;
if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i)))
InV = ConstantExpr::getCompare(CI->getPredicate(), InC, C);
else if (isa<ICmpInst>(CI))
InV = Builder->CreateICmp(CI->getPredicate(), PN->getIncomingValue(i),
C, "phitmp");
else
InV = Builder->CreateFCmp(CI->getPredicate(), PN->getIncomingValue(i),
C, "phitmp");
NewPN->addIncoming(InV, PN->getIncomingBlock(i));
}
} else if (auto *BO = dyn_cast<BinaryOperator>(&I)) {
for (unsigned i = 0; i != NumPHIValues; ++i) {
Value *InV = foldOperationIntoPhiValue(BO, PN->getIncomingValue(i), this);
NewPN->addIncoming(InV, PN->getIncomingBlock(i));
}
} else {
CastInst *CI = cast<CastInst>(&I);
Type *RetTy = CI->getType();
for (unsigned i = 0; i != NumPHIValues; ++i) {
Value *InV;
if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i)))
InV = ConstantExpr::getCast(CI->getOpcode(), InC, RetTy);
else
InV = Builder->CreateCast(CI->getOpcode(),
PN->getIncomingValue(i), I.getType(), "phitmp");
NewPN->addIncoming(InV, PN->getIncomingBlock(i));
}
}
for (auto UI = PN->user_begin(), E = PN->user_end(); UI != E;) {
Instruction *User = cast<Instruction>(*UI++);
if (User == &I) continue;
replaceInstUsesWith(*User, NewPN);
eraseInstFromFunction(*User);
}
return replaceInstUsesWith(I, NewPN);
}
Instruction *InstCombiner::foldOpWithConstantIntoOperand(BinaryOperator &I) {
assert(isa<Constant>(I.getOperand(1)) && "Unexpected operand type");
if (auto *Sel = dyn_cast<SelectInst>(I.getOperand(0))) {
if (Instruction *NewSel = FoldOpIntoSelect(I, Sel))
return NewSel;
} else if (auto *PN = dyn_cast<PHINode>(I.getOperand(0))) {
if (Instruction *NewPhi = foldOpIntoPhi(I, PN))
return NewPhi;
}
return nullptr;
}
/// Given a pointer type and a constant offset, determine whether or not there
/// is a sequence of GEP indices into the pointed type that will land us at the
/// specified offset. If so, fill them into NewIndices and return the resultant
/// element type, otherwise return null.
Type *InstCombiner::FindElementAtOffset(PointerType *PtrTy, int64_t Offset,
SmallVectorImpl<Value *> &NewIndices) {
Type *Ty = PtrTy->getElementType();
if (!Ty->isSized())
return nullptr;
// Start with the index over the outer type. Note that the type size
// might be zero (even if the offset isn't zero) if the indexed type
// is something like [0 x {int, int}]
Type *IntPtrTy = DL.getIntPtrType(PtrTy);
int64_t FirstIdx = 0;
if (int64_t TySize = DL.getTypeAllocSize(Ty)) {
FirstIdx = Offset/TySize;
Offset -= FirstIdx*TySize;
// Handle hosts where % returns negative instead of values [0..TySize).
if (Offset < 0) {
--FirstIdx;
Offset += TySize;
assert(Offset >= 0);
}
assert((uint64_t)Offset < (uint64_t)TySize && "Out of range offset");
}
NewIndices.push_back(ConstantInt::get(IntPtrTy, FirstIdx));
// Index into the types. If we fail, set OrigBase to null.
while (Offset) {
// Indexing into tail padding between struct/array elements.
if (uint64_t(Offset * 8) >= DL.getTypeSizeInBits(Ty))
return nullptr;
if (StructType *STy = dyn_cast<StructType>(Ty)) {
const StructLayout *SL = DL.getStructLayout(STy);
assert(Offset < (int64_t)SL->getSizeInBytes() &&
"Offset must stay within the indexed type");
unsigned Elt = SL->getElementContainingOffset(Offset);
NewIndices.push_back(ConstantInt::get(Type::getInt32Ty(Ty->getContext()),
Elt));
Offset -= SL->getElementOffset(Elt);
Ty = STy->getElementType(Elt);
} else if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
uint64_t EltSize = DL.getTypeAllocSize(AT->getElementType());
assert(EltSize && "Cannot index into a zero-sized array");
NewIndices.push_back(ConstantInt::get(IntPtrTy,Offset/EltSize));
Offset %= EltSize;
Ty = AT->getElementType();
} else {
// Otherwise, we can't index into the middle of this atomic type, bail.
return nullptr;
}
}
return Ty;
}
static bool shouldMergeGEPs(GEPOperator &GEP, GEPOperator &Src) {
// If this GEP has only 0 indices, it is the same pointer as
// Src. If Src is not a trivial GEP too, don't combine
// the indices.
if (GEP.hasAllZeroIndices() && !Src.hasAllZeroIndices() &&
!Src.hasOneUse())
return false;
return true;
}
/// Return a value X such that Val = X * Scale, or null if none.
/// If the multiplication is known not to overflow, then NoSignedWrap is set.
Value *InstCombiner::Descale(Value *Val, APInt Scale, bool &NoSignedWrap) {
assert(isa<IntegerType>(Val->getType()) && "Can only descale integers!");
assert(cast<IntegerType>(Val->getType())->getBitWidth() ==
Scale.getBitWidth() && "Scale not compatible with value!");
// If Val is zero or Scale is one then Val = Val * Scale.
if (match(Val, m_Zero()) || Scale == 1) {
NoSignedWrap = true;
return Val;
}
// If Scale is zero then it does not divide Val.
if (Scale.isMinValue())
return nullptr;
// Look through chains of multiplications, searching for a constant that is
// divisible by Scale. For example, descaling X*(Y*(Z*4)) by a factor of 4
// will find the constant factor 4 and produce X*(Y*Z). Descaling X*(Y*8) by
// a factor of 4 will produce X*(Y*2). The principle of operation is to bore
// down from Val:
//
// Val = M1 * X || Analysis starts here and works down
// M1 = M2 * Y || Doesn't descend into terms with more
// M2 = Z * 4 \/ than one use
//
// Then to modify a term at the bottom:
//
// Val = M1 * X
// M1 = Z * Y || Replaced M2 with Z
//
// Then to work back up correcting nsw flags.
// Op - the term we are currently analyzing. Starts at Val then drills down.
// Replaced with its descaled value before exiting from the drill down loop.
Value *Op = Val;
// Parent - initially null, but after drilling down notes where Op came from.
// In the example above, Parent is (Val, 0) when Op is M1, because M1 is the
// 0'th operand of Val.
std::pair<Instruction*, unsigned> Parent;
// Set if the transform requires a descaling at deeper levels that doesn't
// overflow.
bool RequireNoSignedWrap = false;
// Log base 2 of the scale. Negative if not a power of 2.
int32_t logScale = Scale.exactLogBase2();
for (;; Op = Parent.first->getOperand(Parent.second)) { // Drill down
if (ConstantInt *CI = dyn_cast<ConstantInt>(Op)) {
// If Op is a constant divisible by Scale then descale to the quotient.
APInt Quotient(Scale), Remainder(Scale); // Init ensures right bitwidth.
APInt::sdivrem(CI->getValue(), Scale, Quotient, Remainder);
if (!Remainder.isMinValue())
// Not divisible by Scale.
return nullptr;
// Replace with the quotient in the parent.
Op = ConstantInt::get(CI->getType(), Quotient);
NoSignedWrap = true;
break;
}
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op)) {
if (BO->getOpcode() == Instruction::Mul) {
// Multiplication.
NoSignedWrap = BO->hasNoSignedWrap();
if (RequireNoSignedWrap && !NoSignedWrap)
return nullptr;
// There are three cases for multiplication: multiplication by exactly
// the scale, multiplication by a constant different to the scale, and
// multiplication by something else.
Value *LHS = BO->getOperand(0);
Value *RHS = BO->getOperand(1);
if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
// Multiplication by a constant.
if (CI->getValue() == Scale) {
// Multiplication by exactly the scale, replace the multiplication
// by its left-hand side in the parent.
Op = LHS;
break;
}
// Otherwise drill down into the constant.
if (!Op->hasOneUse())
return nullptr;
Parent = std::make_pair(BO, 1);
continue;
}
// Multiplication by something else. Drill down into the left-hand side
// since that's where the reassociate pass puts the good stuff.
if (!Op->hasOneUse())
return nullptr;
Parent = std::make_pair(BO, 0);
continue;
}
if (logScale > 0 && BO->getOpcode() == Instruction::Shl &&
isa<ConstantInt>(BO->getOperand(1))) {
// Multiplication by a power of 2.
NoSignedWrap = BO->hasNoSignedWrap();
if (RequireNoSignedWrap && !NoSignedWrap)
return nullptr;
Value *LHS = BO->getOperand(0);
int32_t Amt = cast<ConstantInt>(BO->getOperand(1))->
getLimitedValue(Scale.getBitWidth());
// Op = LHS << Amt.
if (Amt == logScale) {
// Multiplication by exactly the scale, replace the multiplication
// by its left-hand side in the parent.
Op = LHS;
break;
}
if (Amt < logScale || !Op->hasOneUse())
return nullptr;
// Multiplication by more than the scale. Reduce the multiplying amount
// by the scale in the parent.
Parent = std::make_pair(BO, 1);
Op = ConstantInt::get(BO->getType(), Amt - logScale);
break;
}
}
if (!Op->hasOneUse())
return nullptr;
if (CastInst *Cast = dyn_cast<CastInst>(Op)) {
if (Cast->getOpcode() == Instruction::SExt) {
// Op is sign-extended from a smaller type, descale in the smaller type.
unsigned SmallSize = Cast->getSrcTy()->getPrimitiveSizeInBits();
APInt SmallScale = Scale.trunc(SmallSize);
// Suppose Op = sext X, and we descale X as Y * SmallScale. We want to
// descale Op as (sext Y) * Scale. In order to have
// sext (Y * SmallScale) = (sext Y) * Scale
// some conditions need to hold however: SmallScale must sign-extend to
// Scale and the multiplication Y * SmallScale should not overflow.
if (SmallScale.sext(Scale.getBitWidth()) != Scale)
// SmallScale does not sign-extend to Scale.
return nullptr;
assert(SmallScale.exactLogBase2() == logScale);
// Require that Y * SmallScale must not overflow.
RequireNoSignedWrap = true;
// Drill down through the cast.
Parent = std::make_pair(Cast, 0);
Scale = SmallScale;
continue;
}
if (Cast->getOpcode() == Instruction::Trunc) {
// Op is truncated from a larger type, descale in the larger type.
// Suppose Op = trunc X, and we descale X as Y * sext Scale. Then
// trunc (Y * sext Scale) = (trunc Y) * Scale
// always holds. However (trunc Y) * Scale may overflow even if
// trunc (Y * sext Scale) does not, so nsw flags need to be cleared
// from this point up in the expression (see later).
if (RequireNoSignedWrap)
return nullptr;
// Drill down through the cast.
unsigned LargeSize = Cast->getSrcTy()->getPrimitiveSizeInBits();
Parent = std::make_pair(Cast, 0);
Scale = Scale.sext(LargeSize);
if (logScale + 1 == (int32_t)Cast->getType()->getPrimitiveSizeInBits())
logScale = -1;
assert(Scale.exactLogBase2() == logScale);
continue;
}
}
// Unsupported expression, bail out.
return nullptr;
}
// If Op is zero then Val = Op * Scale.
if (match(Op, m_Zero())) {
NoSignedWrap = true;
return Op;
}
// We know that we can successfully descale, so from here on we can safely
// modify the IR. Op holds the descaled version of the deepest term in the
// expression. NoSignedWrap is 'true' if multiplying Op by Scale is known
// not to overflow.
if (!Parent.first)
// The expression only had one term.
return Op;
// Rewrite the parent using the descaled version of its operand.
assert(Parent.first->hasOneUse() && "Drilled down when more than one use!");
assert(Op != Parent.first->getOperand(Parent.second) &&
"Descaling was a no-op?");
Parent.first->setOperand(Parent.second, Op);
Worklist.Add(Parent.first);
// Now work back up the expression correcting nsw flags. The logic is based
// on the following observation: if X * Y is known not to overflow as a signed
// multiplication, and Y is replaced by a value Z with smaller absolute value,
// then X * Z will not overflow as a signed multiplication either. As we work
// our way up, having NoSignedWrap 'true' means that the descaled value at the
// current level has strictly smaller absolute value than the original.
Instruction *Ancestor = Parent.first;
do {
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Ancestor)) {
// If the multiplication wasn't nsw then we can't say anything about the
// value of the descaled multiplication, and we have to clear nsw flags
// from this point on up.
bool OpNoSignedWrap = BO->hasNoSignedWrap();
NoSignedWrap &= OpNoSignedWrap;
if (NoSignedWrap != OpNoSignedWrap) {
BO->setHasNoSignedWrap(NoSignedWrap);
Worklist.Add(Ancestor);
}
} else if (Ancestor->getOpcode() == Instruction::Trunc) {
// The fact that the descaled input to the trunc has smaller absolute
// value than the original input doesn't tell us anything useful about
// the absolute values of the truncations.
NoSignedWrap = false;
}
assert((Ancestor->getOpcode() != Instruction::SExt || NoSignedWrap) &&
"Failed to keep proper track of nsw flags while drilling down?");
if (Ancestor == Val)
// Got to the top, all done!
return Val;
// Move up one level in the expression.
assert(Ancestor->hasOneUse() && "Drilled down when more than one use!");
Ancestor = Ancestor->user_back();
} while (1);
}
/// \brief Creates node of binary operation with the same attributes as the
/// specified one but with other operands.
static Value *CreateBinOpAsGiven(BinaryOperator &Inst, Value *LHS, Value *RHS,
InstCombiner::BuilderTy *B) {
Value *BO = B->CreateBinOp(Inst.getOpcode(), LHS, RHS);
// If LHS and RHS are constant, BO won't be a binary operator.
if (BinaryOperator *NewBO = dyn_cast<BinaryOperator>(BO))
NewBO->copyIRFlags(&Inst);
return BO;
}
/// \brief Makes transformation of binary operation specific for vector types.
/// \param Inst Binary operator to transform.
/// \return Pointer to node that must replace the original binary operator, or
/// null pointer if no transformation was made.
Value *InstCombiner::SimplifyVectorOp(BinaryOperator &Inst) {
if (!Inst.getType()->isVectorTy()) return nullptr;
// It may not be safe to reorder shuffles and things like div, urem, etc.
// because we may trap when executing those ops on unknown vector elements.
// See PR20059.
if (!isSafeToSpeculativelyExecute(&Inst))
return nullptr;
unsigned VWidth = cast<VectorType>(Inst.getType())->getNumElements();
Value *LHS = Inst.getOperand(0), *RHS = Inst.getOperand(1);
assert(cast<VectorType>(LHS->getType())->getNumElements() == VWidth);
assert(cast<VectorType>(RHS->getType())->getNumElements() == VWidth);
// If both arguments of the binary operation are shuffles that use the same
// mask and shuffle within a single vector, move the shuffle after the binop:
// Op(shuffle(v1, m), shuffle(v2, m)) -> shuffle(Op(v1, v2), m)
auto *LShuf = dyn_cast<ShuffleVectorInst>(LHS);
auto *RShuf = dyn_cast<ShuffleVectorInst>(RHS);
if (LShuf && RShuf && LShuf->getMask() == RShuf->getMask() &&
isa<UndefValue>(LShuf->getOperand(1)) &&
isa<UndefValue>(RShuf->getOperand(1)) &&
LShuf->getOperand(0)->getType() == RShuf->getOperand(0)->getType()) {
Value *NewBO = CreateBinOpAsGiven(Inst, LShuf->getOperand(0),
RShuf->getOperand(0), Builder);
return Builder->CreateShuffleVector(
NewBO, UndefValue::get(NewBO->getType()), LShuf->getMask());
}
// If one argument is a shuffle within one vector, the other is a constant,
// try moving the shuffle after the binary operation.
ShuffleVectorInst *Shuffle = nullptr;
Constant *C1 = nullptr;
if (isa<ShuffleVectorInst>(LHS)) Shuffle = cast<ShuffleVectorInst>(LHS);
if (isa<ShuffleVectorInst>(RHS)) Shuffle = cast<ShuffleVectorInst>(RHS);
if (isa<Constant>(LHS)) C1 = cast<Constant>(LHS);
if (isa<Constant>(RHS)) C1 = cast<Constant>(RHS);
if (Shuffle && C1 &&
(isa<ConstantVector>(C1) || isa<ConstantDataVector>(C1)) &&
isa<UndefValue>(Shuffle->getOperand(1)) &&
Shuffle->getType() == Shuffle->getOperand(0)->getType()) {
SmallVector<int, 16> ShMask = Shuffle->getShuffleMask();
// Find constant C2 that has property:
// shuffle(C2, ShMask) = C1
// If such constant does not exist (example: ShMask=<0,0> and C1=<1,2>)
// reorder is not possible.
SmallVector<Constant*, 16> C2M(VWidth,
UndefValue::get(C1->getType()->getScalarType()));
bool MayChange = true;
for (unsigned I = 0; I < VWidth; ++I) {
if (ShMask[I] >= 0) {
assert(ShMask[I] < (int)VWidth);
if (!isa<UndefValue>(C2M[ShMask[I]])) {
MayChange = false;
break;
}
C2M[ShMask[I]] = C1->getAggregateElement(I);
}
}
if (MayChange) {
Constant *C2 = ConstantVector::get(C2M);
Value *NewLHS = isa<Constant>(LHS) ? C2 : Shuffle->getOperand(0);
Value *NewRHS = isa<Constant>(LHS) ? Shuffle->getOperand(0) : C2;
Value *NewBO = CreateBinOpAsGiven(Inst, NewLHS, NewRHS, Builder);
return Builder->CreateShuffleVector(NewBO,
UndefValue::get(Inst.getType()), Shuffle->getMask());
}
}
return nullptr;
}
Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
SmallVector<Value*, 8> Ops(GEP.op_begin(), GEP.op_end());
if (Value *V = SimplifyGEPInst(GEP.getSourceElementType(), Ops, SQ))
return replaceInstUsesWith(GEP, V);
Value *PtrOp = GEP.getOperand(0);
// Eliminate unneeded casts for indices, and replace indices which displace
// by multiples of a zero size type with zero.
bool MadeChange = false;
Type *IntPtrTy =
DL.getIntPtrType(GEP.getPointerOperandType()->getScalarType());
gep_type_iterator GTI = gep_type_begin(GEP);
for (User::op_iterator I = GEP.op_begin() + 1, E = GEP.op_end(); I != E;
++I, ++GTI) {
// Skip indices into struct types.
if (GTI.isStruct())
continue;
// Index type should have the same width as IntPtr
Type *IndexTy = (*I)->getType();
Type *NewIndexType = IndexTy->isVectorTy() ?
VectorType::get(IntPtrTy, IndexTy->getVectorNumElements()) : IntPtrTy;
// If the element type has zero size then any index over it is equivalent
// to an index of zero, so replace it with zero if it is not zero already.
Type *EltTy = GTI.getIndexedType();
if (EltTy->isSized() && DL.getTypeAllocSize(EltTy) == 0)
if (!isa<Constant>(*I) || !cast<Constant>(*I)->isNullValue()) {
*I = Constant::getNullValue(NewIndexType);
MadeChange = true;
}
if (IndexTy != NewIndexType) {
// If we are using a wider index than needed for this platform, shrink
// it to what we need. If narrower, sign-extend it to what we need.
// This explicit cast can make subsequent optimizations more obvious.
*I = Builder->CreateIntCast(*I, NewIndexType, true);
MadeChange = true;
}
}
if (MadeChange)
return &GEP;
// Check to see if the inputs to the PHI node are getelementptr instructions.
if (PHINode *PN = dyn_cast<PHINode>(PtrOp)) {
GetElementPtrInst *Op1 = dyn_cast<GetElementPtrInst>(PN->getOperand(0));
if (!Op1)
return nullptr;
// Don't fold a GEP into itself through a PHI node. This can only happen
// through the back-edge of a loop. Folding a GEP into itself means that
// the value of the previous iteration needs to be stored in the meantime,
// thus requiring an additional register variable to be live, but not
// actually achieving anything (the GEP still needs to be executed once per
// loop iteration).
if (Op1 == &GEP)
return nullptr;
int DI = -1;
for (auto I = PN->op_begin()+1, E = PN->op_end(); I !=E; ++I) {
GetElementPtrInst *Op2 = dyn_cast<GetElementPtrInst>(*I);
if (!Op2 || Op1->getNumOperands() != Op2->getNumOperands())
return nullptr;
// As for Op1 above, don't try to fold a GEP into itself.
if (Op2 == &GEP)
return nullptr;
// Keep track of the type as we walk the GEP.
Type *CurTy = nullptr;
for (unsigned J = 0, F = Op1->getNumOperands(); J != F; ++J) {
if (Op1->getOperand(J)->getType() != Op2->getOperand(J)->getType())
return nullptr;
if (Op1->getOperand(J) != Op2->getOperand(J)) {
if (DI == -1) {
// We have not seen any differences yet in the GEPs feeding the
// PHI yet, so we record this one if it is allowed to be a
// variable.
// The first two arguments can vary for any GEP, the rest have to be
// static for struct slots
if (J > 1 && CurTy->isStructTy())
return nullptr;
DI = J;
} else {
// The GEP is different by more than one input. While this could be
// extended to support GEPs that vary by more than one variable it
// doesn't make sense since it greatly increases the complexity and
// would result in an R+R+R addressing mode which no backend
// directly supports and would need to be broken into several
// simpler instructions anyway.
return nullptr;
}
}
// Sink down a layer of the type for the next iteration.
if (J > 0) {
if (J == 1) {
CurTy = Op1->getSourceElementType();
} else if (CompositeType *CT = dyn_cast<CompositeType>(CurTy)) {
CurTy = CT->getTypeAtIndex(Op1->getOperand(J));
} else {
CurTy = nullptr;
}
}
}
}
// If not all GEPs are identical we'll have to create a new PHI node.
// Check that the old PHI node has only one use so that it will get
// removed.
if (DI != -1 && !PN->hasOneUse())
return nullptr;
GetElementPtrInst *NewGEP = cast<GetElementPtrInst>(Op1->clone());
if (DI == -1) {
// All the GEPs feeding the PHI are identical. Clone one down into our
// BB so that it can be merged with the current GEP.
GEP.getParent()->getInstList().insert(
GEP.getParent()->getFirstInsertionPt(), NewGEP);
} else {
// All the GEPs feeding the PHI differ at a single offset. Clone a GEP
// into the current block so it can be merged, and create a new PHI to
// set that index.
PHINode *NewPN;
{
IRBuilderBase::InsertPointGuard Guard(*Builder);
Builder->SetInsertPoint(PN);
NewPN = Builder->CreatePHI(Op1->getOperand(DI)->getType(),
PN->getNumOperands());
}
for (auto &I : PN->operands())
NewPN->addIncoming(cast<GEPOperator>(I)->getOperand(DI),
PN->getIncomingBlock(I));
NewGEP->setOperand(DI, NewPN);
GEP.getParent()->getInstList().insert(
GEP.getParent()->getFirstInsertionPt(), NewGEP);
NewGEP->setOperand(DI, NewPN);
}
GEP.setOperand(0, NewGEP);
PtrOp = NewGEP;
}
// Combine Indices - If the source pointer to this getelementptr instruction
// is a getelementptr instruction, combine the indices of the two
// getelementptr instructions into a single instruction.
//
if (GEPOperator *Src = dyn_cast<GEPOperator>(PtrOp)) {
if (!shouldMergeGEPs(*cast<GEPOperator>(&GEP), *Src))
return nullptr;
// Note that if our source is a gep chain itself then we wait for that
// chain to be resolved before we perform this transformation. This
// avoids us creating a TON of code in some cases.
if (GEPOperator *SrcGEP =
dyn_cast<GEPOperator>(Src->getOperand(0)))
if (SrcGEP->getNumOperands() == 2 && shouldMergeGEPs(*Src, *SrcGEP))
return nullptr; // Wait until our source is folded to completion.
SmallVector<Value*, 8> Indices;
// Find out whether the last index in the source GEP is a sequential idx.
bool EndsWithSequential = false;
for (gep_type_iterator I = gep_type_begin(*Src), E = gep_type_end(*Src);
I != E; ++I)
EndsWithSequential = I.isSequential();
// Can we combine the two pointer arithmetics offsets?
if (EndsWithSequential) {
// Replace: gep (gep %P, long B), long A, ...
// With: T = long A+B; gep %P, T, ...
//
Value *SO1 = Src->getOperand(Src->getNumOperands()-1);
Value *GO1 = GEP.getOperand(1);
// If they aren't the same type, then the input hasn't been processed
// by the loop above yet (which canonicalizes sequential index types to
// intptr_t). Just avoid transforming this until the input has been
// normalized.
if (SO1->getType() != GO1->getType())
return nullptr;
Value *Sum = SimplifyAddInst(GO1, SO1, false, false, SQ);
// Only do the combine when we are sure the cost after the
// merge is never more than that before the merge.
if (Sum == nullptr)
return nullptr;
// Update the GEP in place if possible.
if (Src->getNumOperands() == 2) {
GEP.setOperand(0, Src->getOperand(0));
GEP.setOperand(1, Sum);
return &GEP;
}
Indices.append(Src->op_begin()+1, Src->op_end()-1);
Indices.push_back(Sum);
Indices.append(GEP.op_begin()+2, GEP.op_end());
} else if (isa<Constant>(*GEP.idx_begin()) &&
cast<Constant>(*GEP.idx_begin())->isNullValue() &&
Src->getNumOperands() != 1) {
// Otherwise we can do the fold if the first index of the GEP is a zero
Indices.append(Src->op_begin()+1, Src->op_end());
Indices.append(GEP.idx_begin()+1, GEP.idx_end());
}
if (!Indices.empty())
return GEP.isInBounds() && Src->isInBounds()
? GetElementPtrInst::CreateInBounds(
Src->getSourceElementType(), Src->getOperand(0), Indices,
GEP.getName())
: GetElementPtrInst::Create(Src->getSourceElementType(),
Src->getOperand(0), Indices,
GEP.getName());
}
if (GEP.getNumIndices() == 1) {
unsigned AS = GEP.getPointerAddressSpace();
if (GEP.getOperand(1)->getType()->getScalarSizeInBits() ==
DL.getPointerSizeInBits(AS)) {
Type *Ty = GEP.getSourceElementType();
uint64_t TyAllocSize = DL.getTypeAllocSize(Ty);
bool Matched = false;
uint64_t C;
Value *V = nullptr;
if (TyAllocSize == 1) {
V = GEP.getOperand(1);
Matched = true;
} else if (match(GEP.getOperand(1),
m_AShr(m_Value(V), m_ConstantInt(C)))) {
if (TyAllocSize == 1ULL << C)
Matched = true;
} else if (match(GEP.getOperand(1),
m_SDiv(m_Value(V), m_ConstantInt(C)))) {
if (TyAllocSize == C)
Matched = true;
}
if (Matched) {
// Canonicalize (gep i8* X, -(ptrtoint Y))
// to (inttoptr (sub (ptrtoint X), (ptrtoint Y)))
// The GEP pattern is emitted by the SCEV expander for certain kinds of
// pointer arithmetic.
if (match(V, m_Neg(m_PtrToInt(m_Value())))) {
Operator *Index = cast<Operator>(V);
Value *PtrToInt = Builder->CreatePtrToInt(PtrOp, Index->getType());
Value *NewSub = Builder->CreateSub(PtrToInt, Index->getOperand(1));
return CastInst::Create(Instruction::IntToPtr, NewSub, GEP.getType());
}
// Canonicalize (gep i8* X, (ptrtoint Y)-(ptrtoint X))
// to (bitcast Y)
Value *Y;
if (match(V, m_Sub(m_PtrToInt(m_Value(Y)),
m_PtrToInt(m_Specific(GEP.getOperand(0)))))) {
return CastInst::CreatePointerBitCastOrAddrSpaceCast(Y,
GEP.getType());
}
}
}
}
// We do not handle pointer-vector geps here.
if (GEP.getType()->isVectorTy())
return nullptr;
// Handle gep(bitcast x) and gep(gep x, 0, 0, 0).
Value *StrippedPtr = PtrOp->stripPointerCasts();
PointerType *StrippedPtrTy = cast<PointerType>(StrippedPtr->getType());
if (StrippedPtr != PtrOp) {
bool HasZeroPointerIndex = false;
if (ConstantInt *C = dyn_cast<ConstantInt>(GEP.getOperand(1)))
HasZeroPointerIndex = C->isZero();
// Transform: GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ...
// into : GEP [10 x i8]* X, i32 0, ...
//
// Likewise, transform: GEP (bitcast i8* X to [0 x i8]*), i32 0, ...
// into : GEP i8* X, ...
//
// This occurs when the program declares an array extern like "int X[];"
if (HasZeroPointerIndex) {
if (ArrayType *CATy =
dyn_cast<ArrayType>(GEP.getSourceElementType())) {
// GEP (bitcast i8* X to [0 x i8]*), i32 0, ... ?
if (CATy->getElementType() == StrippedPtrTy->getElementType()) {
// -> GEP i8* X, ...
SmallVector<Value*, 8> Idx(GEP.idx_begin()+1, GEP.idx_end());
GetElementPtrInst *Res = GetElementPtrInst::Create(
StrippedPtrTy->getElementType(), StrippedPtr, Idx, GEP.getName());
Res->setIsInBounds(GEP.isInBounds());
if (StrippedPtrTy->getAddressSpace() == GEP.getAddressSpace())
return Res;
// Insert Res, and create an addrspacecast.
// e.g.,
// GEP (addrspacecast i8 addrspace(1)* X to [0 x i8]*), i32 0, ...
// ->
// %0 = GEP i8 addrspace(1)* X, ...
// addrspacecast i8 addrspace(1)* %0 to i8*
return new AddrSpaceCastInst(Builder->Insert(Res), GEP.getType());
}
if (ArrayType *XATy =
dyn_cast<ArrayType>(StrippedPtrTy->getElementType())){
// GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ... ?
if (CATy->getElementType() == XATy->getElementType()) {
// -> GEP [10 x i8]* X, i32 0, ...
// At this point, we know that the cast source type is a pointer
// to an array of the same type as the destination pointer
// array. Because the array type is never stepped over (there
// is a leading zero) we can fold the cast into this GEP.
if (StrippedPtrTy->getAddressSpace() == GEP.getAddressSpace()) {
GEP.setOperand(0, StrippedPtr);
GEP.setSourceElementType(XATy);
return &GEP;
}
// Cannot replace the base pointer directly because StrippedPtr's
// address space is different. Instead, create a new GEP followed by
// an addrspacecast.
// e.g.,
// GEP (addrspacecast [10 x i8] addrspace(1)* X to [0 x i8]*),
// i32 0, ...
// ->
// %0 = GEP [10 x i8] addrspace(1)* X, ...
// addrspacecast i8 addrspace(1)* %0 to i8*
SmallVector<Value*, 8> Idx(GEP.idx_begin(), GEP.idx_end());
Value *NewGEP = GEP.isInBounds()
? Builder->CreateInBoundsGEP(
nullptr, StrippedPtr, Idx, GEP.getName())
: Builder->CreateGEP(nullptr, StrippedPtr, Idx,
GEP.getName());
return new AddrSpaceCastInst(NewGEP, GEP.getType());
}
}
}
} else if (GEP.getNumOperands() == 2) {
// Transform things like:
// %t = getelementptr i32* bitcast ([2 x i32]* %str to i32*), i32 %V
// into: %t1 = getelementptr [2 x i32]* %str, i32 0, i32 %V; bitcast
Type *SrcElTy = StrippedPtrTy->getElementType();
Type *ResElTy = GEP.getSourceElementType();
if (SrcElTy->isArrayTy() &&
DL.getTypeAllocSize(SrcElTy->getArrayElementType()) ==
DL.getTypeAllocSize(ResElTy)) {
Type *IdxType = DL.getIntPtrType(GEP.getType());
Value *Idx[2] = { Constant::getNullValue(IdxType), GEP.getOperand(1) };
Value *NewGEP =
GEP.isInBounds()
? Builder->CreateInBoundsGEP(nullptr, StrippedPtr, Idx,
GEP.getName())
: Builder->CreateGEP(nullptr, StrippedPtr, Idx, GEP.getName());
// V and GEP are both pointer types --> BitCast
return CastInst::CreatePointerBitCastOrAddrSpaceCast(NewGEP,
GEP.getType());
}
// Transform things like:
// %V = mul i64 %N, 4
// %t = getelementptr i8* bitcast (i32* %arr to i8*), i32 %V
// into: %t1 = getelementptr i32* %arr, i32 %N; bitcast
if (ResElTy->isSized() && SrcElTy->isSized()) {
// Check that changing the type amounts to dividing the index by a scale
// factor.
uint64_t ResSize = DL.getTypeAllocSize(ResElTy);
uint64_t SrcSize = DL.getTypeAllocSize(SrcElTy);
if (ResSize && SrcSize % ResSize == 0) {
Value *Idx = GEP.getOperand(1);
unsigned BitWidth = Idx->getType()->getPrimitiveSizeInBits();
uint64_t Scale = SrcSize / ResSize;
// Earlier transforms ensure that the index has type IntPtrType, which
// considerably simplifies the logic by eliminating implicit casts.
assert(Idx->getType() == DL.getIntPtrType(GEP.getType()) &&
"Index not cast to pointer width?");
bool NSW;
if (Value *NewIdx = Descale(Idx, APInt(BitWidth, Scale), NSW)) {
// Successfully decomposed Idx as NewIdx * Scale, form a new GEP.
// If the multiplication NewIdx * Scale may overflow then the new
// GEP may not be "inbounds".
Value *NewGEP =
GEP.isInBounds() && NSW
? Builder->CreateInBoundsGEP(nullptr, StrippedPtr, NewIdx,
GEP.getName())
: Builder->CreateGEP(nullptr, StrippedPtr, NewIdx,
GEP.getName());
// The NewGEP must be pointer typed, so must the old one -> BitCast
return CastInst::CreatePointerBitCastOrAddrSpaceCast(NewGEP,
GEP.getType());
}
}
}
// Similarly, transform things like:
// getelementptr i8* bitcast ([100 x double]* X to i8*), i32 %tmp
// (where tmp = 8*tmp2) into:
// getelementptr [100 x double]* %arr, i32 0, i32 %tmp2; bitcast
if (ResElTy->isSized() && SrcElTy->isSized() && SrcElTy->isArrayTy()) {
// Check that changing to the array element type amounts to dividing the
// index by a scale factor.
uint64_t ResSize = DL.getTypeAllocSize(ResElTy);
uint64_t ArrayEltSize =
DL.getTypeAllocSize(SrcElTy->getArrayElementType());
if (ResSize && ArrayEltSize % ResSize == 0) {
Value *Idx = GEP.getOperand(1);
unsigned BitWidth = Idx->getType()->getPrimitiveSizeInBits();
uint64_t Scale = ArrayEltSize / ResSize;
// Earlier transforms ensure that the index has type IntPtrType, which
// considerably simplifies the logic by eliminating implicit casts.
assert(Idx->getType() == DL.getIntPtrType(GEP.getType()) &&
"Index not cast to pointer width?");
bool NSW;
if (Value *NewIdx = Descale(Idx, APInt(BitWidth, Scale), NSW)) {
// Successfully decomposed Idx as NewIdx * Scale, form a new GEP.
// If the multiplication NewIdx * Scale may overflow then the new
// GEP may not be "inbounds".
Value *Off[2] = {
Constant::getNullValue(DL.getIntPtrType(GEP.getType())),
NewIdx};
Value *NewGEP = GEP.isInBounds() && NSW
? Builder->CreateInBoundsGEP(
SrcElTy, StrippedPtr, Off, GEP.getName())
: Builder->CreateGEP(SrcElTy, StrippedPtr, Off,
GEP.getName());
// The NewGEP must be pointer typed, so must the old one -> BitCast
return CastInst::CreatePointerBitCastOrAddrSpaceCast(NewGEP,
GEP.getType());
}
}
}
}
}
// addrspacecast between types is canonicalized as a bitcast, then an
// addrspacecast. To take advantage of the below bitcast + struct GEP, look
// through the addrspacecast.
if (AddrSpaceCastInst *ASC = dyn_cast<AddrSpaceCastInst>(PtrOp)) {
// X = bitcast A addrspace(1)* to B addrspace(1)*
// Y = addrspacecast A addrspace(1)* to B addrspace(2)*
// Z = gep Y, <...constant indices...>
// Into an addrspacecasted GEP of the struct.
if (BitCastInst *BC = dyn_cast<BitCastInst>(ASC->getOperand(0)))
PtrOp = BC;
}
/// See if we can simplify:
/// X = bitcast A* to B*
/// Y = gep X, <...constant indices...>
/// into a gep of the original struct. This is important for SROA and alias
/// analysis of unions. If "A" is also a bitcast, wait for A/X to be merged.
if (BitCastInst *BCI = dyn_cast<BitCastInst>(PtrOp)) {
Value *Operand = BCI->getOperand(0);
PointerType *OpType = cast<PointerType>(Operand->getType());
unsigned OffsetBits = DL.getPointerTypeSizeInBits(GEP.getType());
APInt Offset(OffsetBits, 0);
if (!isa<BitCastInst>(Operand) &&
GEP.accumulateConstantOffset(DL, Offset)) {
// If this GEP instruction doesn't move the pointer, just replace the GEP
// with a bitcast of the real input to the dest type.
if (!Offset) {
// If the bitcast is of an allocation, and the allocation will be
// converted to match the type of the cast, don't touch this.
if (isa<AllocaInst>(Operand) || isAllocationFn(Operand, &TLI)) {
// See if the bitcast simplifies, if so, don't nuke this GEP yet.
if (Instruction *I = visitBitCast(*BCI)) {
if (I != BCI) {
I->takeName(BCI);
BCI->getParent()->getInstList().insert(BCI->getIterator(), I);
replaceInstUsesWith(*BCI, I);
}
return &GEP;
}
}
if (Operand->getType()->getPointerAddressSpace() != GEP.getAddressSpace())
return new AddrSpaceCastInst(Operand, GEP.getType());
return new BitCastInst(Operand, GEP.getType());
}
// Otherwise, if the offset is non-zero, we need to find out if there is a
// field at Offset in 'A's type. If so, we can pull the cast through the
// GEP.
SmallVector<Value*, 8> NewIndices;
if (FindElementAtOffset(OpType, Offset.getSExtValue(), NewIndices)) {
Value *NGEP =
GEP.isInBounds()
? Builder->CreateInBoundsGEP(nullptr, Operand, NewIndices)
: Builder->CreateGEP(nullptr, Operand, NewIndices);
if (NGEP->getType() == GEP.getType())
return replaceInstUsesWith(GEP, NGEP);
NGEP->takeName(&GEP);
if (NGEP->getType()->getPointerAddressSpace() != GEP.getAddressSpace())
return new AddrSpaceCastInst(NGEP, GEP.getType());
return new BitCastInst(NGEP, GEP.getType());
}
}
}
if (!GEP.isInBounds()) {
unsigned PtrWidth =
DL.getPointerSizeInBits(PtrOp->getType()->getPointerAddressSpace());
APInt BasePtrOffset(PtrWidth, 0);
Value *UnderlyingPtrOp =
PtrOp->stripAndAccumulateInBoundsConstantOffsets(DL,
BasePtrOffset);
if (auto *AI = dyn_cast<AllocaInst>(UnderlyingPtrOp)) {
if (GEP.accumulateConstantOffset(DL, BasePtrOffset) &&
BasePtrOffset.isNonNegative()) {
APInt AllocSize(PtrWidth, DL.getTypeAllocSize(AI->getAllocatedType()));
if (BasePtrOffset.ule(AllocSize)) {
return GetElementPtrInst::CreateInBounds(
PtrOp, makeArrayRef(Ops).slice(1), GEP.getName());
}
}
}
}
return nullptr;
}
static bool isNeverEqualToUnescapedAlloc(Value *V, const TargetLibraryInfo *TLI,
Instruction *AI) {
if (isa<ConstantPointerNull>(V))
return true;
if (auto *LI = dyn_cast<LoadInst>(V))
return isa<GlobalVariable>(LI->getPointerOperand());
// Two distinct allocations will never be equal.
// We rely on LookThroughBitCast in isAllocLikeFn being false, since looking
// through bitcasts of V can cause
// the result statement below to be true, even when AI and V (ex:
// i8* ->i32* ->i8* of AI) are the same allocations.
return isAllocLikeFn(V, TLI) && V != AI;
}
static bool isAllocSiteRemovable(Instruction *AI,
SmallVectorImpl<WeakTrackingVH> &Users,
const TargetLibraryInfo *TLI) {
SmallVector<Instruction*, 4> Worklist;
Worklist.push_back(AI);
do {
Instruction *PI = Worklist.pop_back_val();
for (User *U : PI->users()) {
Instruction *I = cast<Instruction>(U);
switch (I->getOpcode()) {
default:
// Give up the moment we see something we can't handle.
return false;
case Instruction::AddrSpaceCast:
case Instruction::BitCast:
case Instruction::GetElementPtr:
Users.emplace_back(I);
Worklist.push_back(I);
continue;
case Instruction::ICmp: {
ICmpInst *ICI = cast<ICmpInst>(I);
// We can fold eq/ne comparisons with null to false/true, respectively.
// We also fold comparisons in some conditions provided the alloc has
// not escaped (see isNeverEqualToUnescapedAlloc).
if (!ICI->isEquality())
return false;
unsigned OtherIndex = (ICI->getOperand(0) == PI) ? 1 : 0;
if (!isNeverEqualToUnescapedAlloc(ICI->getOperand(OtherIndex), TLI, AI))
return false;
Users.emplace_back(I);
continue;
}
case Instruction::Call:
// Ignore no-op and store intrinsics.
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
switch (II->getIntrinsicID()) {
default:
return false;
case Intrinsic::memmove:
case Intrinsic::memcpy:
case Intrinsic::memset: {
MemIntrinsic *MI = cast<MemIntrinsic>(II);
if (MI->isVolatile() || MI->getRawDest() != PI)
return false;
LLVM_FALLTHROUGH;
}
case Intrinsic::dbg_declare:
case Intrinsic::dbg_value:
case Intrinsic::invariant_start:
case Intrinsic::invariant_end:
case Intrinsic::lifetime_start:
case Intrinsic::lifetime_end:
case Intrinsic::objectsize:
Users.emplace_back(I);
continue;
}
}
if (isFreeCall(I, TLI)) {
Users.emplace_back(I);
continue;
}
return false;
case Instruction::Store: {
StoreInst *SI = cast<StoreInst>(I);
if (SI->isVolatile() || SI->getPointerOperand() != PI)
return false;
Users.emplace_back(I);
continue;
}
}
llvm_unreachable("missing a return?");
}
} while (!Worklist.empty());
return true;
}
Instruction *InstCombiner::visitAllocSite(Instruction &MI) {
// If we have a malloc call which is only used in any amount of comparisons
// to null and free calls, delete the calls and replace the comparisons with
// true or false as appropriate.
SmallVector<WeakTrackingVH, 64> Users;
if (isAllocSiteRemovable(&MI, Users, &TLI)) {
for (unsigned i = 0, e = Users.size(); i != e; ++i) {
// Lowering all @llvm.objectsize calls first because they may
// use a bitcast/GEP of the alloca we are removing.
if (!Users[i])
continue;
Instruction *I = cast<Instruction>(&*Users[i]);
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
if (II->getIntrinsicID() == Intrinsic::objectsize) {
ConstantInt *Result = lowerObjectSizeCall(II, DL, &TLI,
/*MustSucceed=*/true);
replaceInstUsesWith(*I, Result);
eraseInstFromFunction(*I);
Users[i] = nullptr; // Skip examining in the next loop.
}
}
}
for (unsigned i = 0, e = Users.size(); i != e; ++i) {
if (!Users[i])
continue;
Instruction *I = cast<Instruction>(&*Users[i]);
if (ICmpInst *C = dyn_cast<ICmpInst>(I)) {
replaceInstUsesWith(*C,
ConstantInt::get(Type::getInt1Ty(C->getContext()),
C->isFalseWhenEqual()));
} else if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I) ||
isa<AddrSpaceCastInst>(I)) {
replaceInstUsesWith(*I, UndefValue::get(I->getType()));
}
eraseInstFromFunction(*I);
}
if (InvokeInst *II = dyn_cast<InvokeInst>(&MI)) {
// Replace invoke with a NOP intrinsic to maintain the original CFG
Module *M = II->getModule();
Function *F = Intrinsic::getDeclaration(M, Intrinsic::donothing);
InvokeInst::Create(F, II->getNormalDest(), II->getUnwindDest(),
None, "", II->getParent());
}
return eraseInstFromFunction(MI);
}
return nullptr;
}
/// \brief Move the call to free before a NULL test.
///
/// Check if this free is accessed after its argument has been test
/// against NULL (property 0).
/// If yes, it is legal to move this call in its predecessor block.
///
/// The move is performed only if the block containing the call to free
/// will be removed, i.e.:
/// 1. it has only one predecessor P, and P has two successors
/// 2. it contains the call and an unconditional branch
/// 3. its successor is the same as its predecessor's successor
///
/// The profitability is out-of concern here and this function should
/// be called only if the caller knows this transformation would be
/// profitable (e.g., for code size).
static Instruction *
tryToMoveFreeBeforeNullTest(CallInst &FI) {
Value *Op = FI.getArgOperand(0);
BasicBlock *FreeInstrBB = FI.getParent();
BasicBlock *PredBB = FreeInstrBB->getSinglePredecessor();
// Validate part of constraint #1: Only one predecessor
// FIXME: We can extend the number of predecessor, but in that case, we
// would duplicate the call to free in each predecessor and it may
// not be profitable even for code size.
if (!PredBB)
return nullptr;
// Validate constraint #2: Does this block contains only the call to
// free and an unconditional branch?
// FIXME: We could check if we can speculate everything in the
// predecessor block
if (FreeInstrBB->size() != 2)
return nullptr;
BasicBlock *SuccBB;
if (!match(FreeInstrBB->getTerminator(), m_UnconditionalBr(SuccBB)))
return nullptr;
// Validate the rest of constraint #1 by matching on the pred branch.
TerminatorInst *TI = PredBB->getTerminator();
BasicBlock *TrueBB, *FalseBB;
ICmpInst::Predicate Pred;
if (!match(TI, m_Br(m_ICmp(Pred, m_Specific(Op), m_Zero()), TrueBB, FalseBB)))
return nullptr;
if (Pred != ICmpInst::ICMP_EQ && Pred != ICmpInst::ICMP_NE)
return nullptr;
// Validate constraint #3: Ensure the null case just falls through.
if (SuccBB != (Pred == ICmpInst::ICMP_EQ ? TrueBB : FalseBB))
return nullptr;
assert(FreeInstrBB == (Pred == ICmpInst::ICMP_EQ ? FalseBB : TrueBB) &&
"Broken CFG: missing edge from predecessor to successor");
FI.moveBefore(TI);
return &FI;
}
Instruction *InstCombiner::visitFree(CallInst &FI) {
Value *Op = FI.getArgOperand(0);
// free undef -> unreachable.
if (isa<UndefValue>(Op)) {
// Insert a new store to null because we cannot modify the CFG here.
Builder->CreateStore(ConstantInt::getTrue(FI.getContext()),
UndefValue::get(Type::getInt1PtrTy(FI.getContext())));
return eraseInstFromFunction(FI);
}
// If we have 'free null' delete the instruction. This can happen in stl code
// when lots of inlining happens.
if (isa<ConstantPointerNull>(Op))
return eraseInstFromFunction(FI);
// If we optimize for code size, try to move the call to free before the null
// test so that simplify cfg can remove the empty block and dead code
// elimination the branch. I.e., helps to turn something like:
// if (foo) free(foo);
// into
// free(foo);
if (MinimizeSize)
if (Instruction *I = tryToMoveFreeBeforeNullTest(FI))
return I;
return nullptr;
}
Instruction *InstCombiner::visitReturnInst(ReturnInst &RI) {
if (RI.getNumOperands() == 0) // ret void
return nullptr;
Value *ResultOp = RI.getOperand(0);
Type *VTy = ResultOp->getType();
if (!VTy->isIntegerTy())
return nullptr;
// There might be assume intrinsics dominating this return that completely
// determine the value. If so, constant fold it.
KnownBits Known = computeKnownBits(ResultOp, 0, &RI);
if (Known.isConstant())
RI.setOperand(0, Constant::getIntegerValue(VTy, Known.getConstant()));
return nullptr;
}
Instruction *InstCombiner::visitBranchInst(BranchInst &BI) {
// Change br (not X), label True, label False to: br X, label False, True
Value *X = nullptr;
BasicBlock *TrueDest;
BasicBlock *FalseDest;
if (match(&BI, m_Br(m_Not(m_Value(X)), TrueDest, FalseDest)) &&
!isa<Constant>(X)) {
// Swap Destinations and condition...
BI.setCondition(X);
BI.swapSuccessors();
return &BI;
}
// If the condition is irrelevant, remove the use so that other
// transforms on the condition become more effective.
if (BI.isConditional() &&
BI.getSuccessor(0) == BI.getSuccessor(1) &&
!isa<UndefValue>(BI.getCondition())) {
BI.setCondition(UndefValue::get(BI.getCondition()->getType()));
return &BI;
}
// Canonicalize, for example, icmp_ne -> icmp_eq or fcmp_one -> fcmp_oeq.
CmpInst::Predicate Pred;
if (match(&BI, m_Br(m_OneUse(m_Cmp(Pred, m_Value(), m_Value())), TrueDest,
FalseDest)) &&
!isCanonicalPredicate(Pred)) {
// Swap destinations and condition.
CmpInst *Cond = cast<CmpInst>(BI.getCondition());
Cond->setPredicate(CmpInst::getInversePredicate(Pred));
BI.swapSuccessors();
Worklist.Add(Cond);
return &BI;
}
return nullptr;
}
Instruction *InstCombiner::visitSwitchInst(SwitchInst &SI) {
Value *Cond = SI.getCondition();
Value *Op0;
ConstantInt *AddRHS;
if (match(Cond, m_Add(m_Value(Op0), m_ConstantInt(AddRHS)))) {
// Change 'switch (X+4) case 1:' into 'switch (X) case -3'.
for (auto Case : SI.cases()) {
Constant *NewCase = ConstantExpr::getSub(Case.getCaseValue(), AddRHS);
assert(isa<ConstantInt>(NewCase) &&
"Result of expression should be constant");
Case.setValue(cast<ConstantInt>(NewCase));
}
SI.setCondition(Op0);
return &SI;
}
KnownBits Known = computeKnownBits(Cond, 0, &SI);
unsigned LeadingKnownZeros = Known.countMinLeadingZeros();
unsigned LeadingKnownOnes = Known.countMinLeadingOnes();
// Compute the number of leading bits we can ignore.
// TODO: A better way to determine this would use ComputeNumSignBits().
for (auto &C : SI.cases()) {
LeadingKnownZeros = std::min(
LeadingKnownZeros, C.getCaseValue()->getValue().countLeadingZeros());
LeadingKnownOnes = std::min(
LeadingKnownOnes, C.getCaseValue()->getValue().countLeadingOnes());
}
unsigned NewWidth = Known.getBitWidth() - std::max(LeadingKnownZeros, LeadingKnownOnes);
// Shrink the condition operand if the new type is smaller than the old type.
// This may produce a non-standard type for the switch, but that's ok because
// the backend should extend back to a legal type for the target.
if (NewWidth > 0 && NewWidth < Known.getBitWidth()) {
IntegerType *Ty = IntegerType::get(SI.getContext(), NewWidth);
Builder->SetInsertPoint(&SI);
Value *NewCond = Builder->CreateTrunc(Cond, Ty, "trunc");
SI.setCondition(NewCond);
for (auto Case : SI.cases()) {
APInt TruncatedCase = Case.getCaseValue()->getValue().trunc(NewWidth);
Case.setValue(ConstantInt::get(SI.getContext(), TruncatedCase));
}
return &SI;
}
return nullptr;
}
Instruction *InstCombiner::visitExtractValueInst(ExtractValueInst &EV) {
Value *Agg = EV.getAggregateOperand();
if (!EV.hasIndices())
return replaceInstUsesWith(EV, Agg);
if (Value *V = SimplifyExtractValueInst(Agg, EV.getIndices(), SQ))
return replaceInstUsesWith(EV, V);
if (InsertValueInst *IV = dyn_cast<InsertValueInst>(Agg)) {
// We're extracting from an insertvalue instruction, compare the indices
const unsigned *exti, *exte, *insi, *inse;
for (exti = EV.idx_begin(), insi = IV->idx_begin(),
exte = EV.idx_end(), inse = IV->idx_end();
exti != exte && insi != inse;
++exti, ++insi) {
if (*insi != *exti)
// The insert and extract both reference distinctly different elements.
// This means the extract is not influenced by the insert, and we can
// replace the aggregate operand of the extract with the aggregate
// operand of the insert. i.e., replace
// %I = insertvalue { i32, { i32 } } %A, { i32 } { i32 42 }, 1
// %E = extractvalue { i32, { i32 } } %I, 0
// with
// %E = extractvalue { i32, { i32 } } %A, 0
return ExtractValueInst::Create(IV->getAggregateOperand(),
EV.getIndices());
}
if (exti == exte && insi == inse)
// Both iterators are at the end: Index lists are identical. Replace
// %B = insertvalue { i32, { i32 } } %A, i32 42, 1, 0
// %C = extractvalue { i32, { i32 } } %B, 1, 0
// with "i32 42"
return replaceInstUsesWith(EV, IV->getInsertedValueOperand());
if (exti == exte) {
// The extract list is a prefix of the insert list. i.e. replace
// %I = insertvalue { i32, { i32 } } %A, i32 42, 1, 0
// %E = extractvalue { i32, { i32 } } %I, 1
// with
// %X = extractvalue { i32, { i32 } } %A, 1
// %E = insertvalue { i32 } %X, i32 42, 0
// by switching the order of the insert and extract (though the
// insertvalue should be left in, since it may have other uses).
Value *NewEV = Builder->CreateExtractValue(IV->getAggregateOperand(),
EV.getIndices());
return InsertValueInst::Create(NewEV, IV->getInsertedValueOperand(),
makeArrayRef(insi, inse));
}
if (insi == inse)
// The insert list is a prefix of the extract list
// We can simply remove the common indices from the extract and make it
// operate on the inserted value instead of the insertvalue result.
// i.e., replace
// %I = insertvalue { i32, { i32 } } %A, { i32 } { i32 42 }, 1
// %E = extractvalue { i32, { i32 } } %I, 1, 0
// with
// %E extractvalue { i32 } { i32 42 }, 0
return ExtractValueInst::Create(IV->getInsertedValueOperand(),
makeArrayRef(exti, exte));
}
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Agg)) {
// We're extracting from an intrinsic, see if we're the only user, which
// allows us to simplify multiple result intrinsics to simpler things that
// just get one value.
if (II->hasOneUse()) {
// Check if we're grabbing the overflow bit or the result of a 'with
// overflow' intrinsic. If it's the latter we can remove the intrinsic
// and replace it with a traditional binary instruction.
switch (II->getIntrinsicID()) {
case Intrinsic::uadd_with_overflow:
case Intrinsic::sadd_with_overflow:
if (*EV.idx_begin() == 0) { // Normal result.
Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
replaceInstUsesWith(*II, UndefValue::get(II->getType()));
eraseInstFromFunction(*II);
return BinaryOperator::CreateAdd(LHS, RHS);
}
// If the normal result of the add is dead, and the RHS is a constant,
// we can transform this into a range comparison.
// overflow = uadd a, -4 --> overflow = icmp ugt a, 3
if (II->getIntrinsicID() == Intrinsic::uadd_with_overflow)
if (ConstantInt *CI = dyn_cast<ConstantInt>(II->getArgOperand(1)))
return new ICmpInst(ICmpInst::ICMP_UGT, II->getArgOperand(0),
ConstantExpr::getNot(CI));
break;
case Intrinsic::usub_with_overflow:
case Intrinsic::ssub_with_overflow:
if (*EV.idx_begin() == 0) { // Normal result.
Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
replaceInstUsesWith(*II, UndefValue::get(II->getType()));
eraseInstFromFunction(*II);
return BinaryOperator::CreateSub(LHS, RHS);
}
break;
case Intrinsic::umul_with_overflow:
case Intrinsic::smul_with_overflow:
if (*EV.idx_begin() == 0) { // Normal result.
Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
replaceInstUsesWith(*II, UndefValue::get(II->getType()));
eraseInstFromFunction(*II);
return BinaryOperator::CreateMul(LHS, RHS);
}
break;
default:
break;
}
}
}
if (LoadInst *L = dyn_cast<LoadInst>(Agg))
// If the (non-volatile) load only has one use, we can rewrite this to a
// load from a GEP. This reduces the size of the load. If a load is used
// only by extractvalue instructions then this either must have been
// optimized before, or it is a struct with padding, in which case we
// don't want to do the transformation as it loses padding knowledge.
if (L->isSimple() && L->hasOneUse()) {
// extractvalue has integer indices, getelementptr has Value*s. Convert.
SmallVector<Value*, 4> Indices;
// Prefix an i32 0 since we need the first element.
Indices.push_back(Builder->getInt32(0));
for (ExtractValueInst::idx_iterator I = EV.idx_begin(), E = EV.idx_end();
I != E; ++I)
Indices.push_back(Builder->getInt32(*I));
// We need to insert these at the location of the old load, not at that of
// the extractvalue.
Builder->SetInsertPoint(L);
Value *GEP = Builder->CreateInBoundsGEP(L->getType(),
L->getPointerOperand(), Indices);
// Returning the load directly will cause the main loop to insert it in
// the wrong spot, so use replaceInstUsesWith().
return replaceInstUsesWith(EV, Builder->CreateLoad(GEP));
}
// We could simplify extracts from other values. Note that nested extracts may
// already be simplified implicitly by the above: extract (extract (insert) )
// will be translated into extract ( insert ( extract ) ) first and then just
// the value inserted, if appropriate. Similarly for extracts from single-use
// loads: extract (extract (load)) will be translated to extract (load (gep))
// and if again single-use then via load (gep (gep)) to load (gep).
// However, double extracts from e.g. function arguments or return values
// aren't handled yet.
return nullptr;
}