Revert "[SCEV] Use isBasicBlockEntryGuardedByCond in isLoopBackedgeGuardedByCond"
This reverts commit 3d4c0460ec6040fc071e56dc113afd181294591e.
Compile time impact is still high. Need to understand why.
Differential Revision: https://reviews.llvm.org/D92153
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index b7bd54a..53fd668 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -9911,7 +9911,42 @@
if (isImpliedViaGuard(Latch, Pred, LHS, RHS))
return true;
- return isBasicBlockEntryGuardedByCond(Latch, Pred, LHS, RHS);
+ for (DomTreeNode *DTN = DT[Latch], *HeaderDTN = DT[L->getHeader()];
+ DTN != HeaderDTN; DTN = DTN->getIDom()) {
+ assert(DTN && "should reach the loop header before reaching the root!");
+
+ BasicBlock *BB = DTN->getBlock();
+ if (isImpliedViaGuard(BB, Pred, LHS, RHS))
+ return true;
+
+ BasicBlock *PBB = BB->getSinglePredecessor();
+ if (!PBB)
+ continue;
+
+ BranchInst *ContinuePredicate = dyn_cast<BranchInst>(PBB->getTerminator());
+ if (!ContinuePredicate || !ContinuePredicate->isConditional())
+ continue;
+
+ Value *Condition = ContinuePredicate->getCondition();
+
+ // If we have an edge `E` within the loop body that dominates the only
+ // latch, the condition guarding `E` also guards the backedge. This
+ // reasoning works only for loops with a single latch.
+
+ BasicBlockEdge DominatingEdge(PBB, BB);
+ if (DominatingEdge.isSingleEdge()) {
+ // We're constructively (and conservatively) enumerating edges within the
+ // loop body that dominate the latch. The dominator tree better agree
+ // with us on this:
+ assert(DT.dominates(DominatingEdge, Latch) && "should be!");
+
+ if (isImpliedCond(Pred, LHS, RHS, Condition,
+ BB != ContinuePredicate->getSuccessor(0)))
+ return true;
+ }
+ }
+
+ return false;
}
bool ScalarEvolution::isBasicBlockEntryGuardedByCond(const BasicBlock *BB,
diff --git a/llvm/test/Transforms/LoopStrengthReduce/post-inc-icmpzero.ll b/llvm/test/Transforms/LoopStrengthReduce/post-inc-icmpzero.ll
index c398289..8a07a49 100644
--- a/llvm/test/Transforms/LoopStrengthReduce/post-inc-icmpzero.ll
+++ b/llvm/test/Transforms/LoopStrengthReduce/post-inc-icmpzero.ll
@@ -69,7 +69,7 @@
; CHECK-NEXT: [[UGLYGEP2:%.*]] = bitcast i8* [[UGLYGEP]] to i16*
; CHECK-NEXT: [[TMP29:%.*]] = load i16, i16* [[LSR_IV810]], align 2
; CHECK-NEXT: store i16 [[TMP29]], i16* [[UGLYGEP2]], align 2
-; CHECK-NEXT: [[LSR_IV_NEXT]] = add nuw nsw i64 [[LSR_IV]], 2
+; CHECK-NEXT: [[LSR_IV_NEXT]] = add i64 [[LSR_IV]], 2
; CHECK-NEXT: [[LSR_IV_NEXT3:%.*]] = inttoptr i64 [[LSR_IV_NEXT]] to i16*
; CHECK-NEXT: [[SCEVGEP9:%.*]] = getelementptr [33 x i16], [33 x i16]* [[LSR_IV8]], i64 0, i64 1
; CHECK-NEXT: [[TMP3]] = bitcast i16* [[SCEVGEP9]] to [33 x i16]*
