src/librustc_mir/build/expr/as_operand.rs

//! See docs in build/expr/mod.rs

use crate::build::expr::category::Category;
use crate::build::{BlockAnd, BlockAndExtension, Builder};
use crate::hair::*;
use rustc::middle::region;
use rustc::mir::*;

impl<'a, 'tcx> Builder<'a, 'tcx> {
    /// Returns an operand suitable for use until the end of the current
    /// scope expression.
    ///
    /// The operand returned from this function will *not be valid* after
    /// an ExprKind::Scope is passed, so please do *not* return it from
    /// functions to avoid bad miscompiles.
    pub fn as_local_operand<M>(&mut self, block: BasicBlock, expr: M) -> BlockAnd<Operand<'tcx>>
    where
        M: Mirror<'tcx, Output = Expr<'tcx>>,
    {
        let local_scope = self.local_scope();
        self.as_operand(block, local_scope, expr)
    }

    /// Compile `expr` into a value that can be used as an operand.
    /// If `expr` is a place like `x`, this will introduce a
    /// temporary `tmp = x`, so that we capture the value of `x` at
    /// this time.
    ///
    /// The operand is known to be live until the end of `scope`.
    pub fn as_operand<M>(
        &mut self,
        block: BasicBlock,
        scope: Option<region::Scope>,
        expr: M,
    ) -> BlockAnd<Operand<'tcx>>
    where
        M: Mirror<'tcx, Output = Expr<'tcx>>,
    {
        let expr = self.hir.mirror(expr);
        self.expr_as_operand(block, scope, expr)
    }

    fn expr_as_operand(
        &mut self,
        mut block: BasicBlock,
        scope: Option<region::Scope>,
        expr: Expr<'tcx>,
    ) -> BlockAnd<Operand<'tcx>> {
        debug!("expr_as_operand(block={:?}, expr={:?})", block, expr);
        let this = self;

        if let ExprKind::Scope {
            region_scope,
            lint_level,
            value,
        } = expr.kind
        {
            let source_info = this.source_info(expr.span);
            let region_scope = (region_scope, source_info);
            return this.in_scope(region_scope, lint_level, |this| {
                this.as_operand(block, scope, value)
            });
        }

        let category = Category::of(&expr.kind).unwrap();
        debug!(
            "expr_as_operand: category={:?} for={:?}",
            category, expr.kind
        );
        match category {
            Category::Constant => {
                let constant = this.as_constant(expr);
                block.and(Operand::Constant(box constant))
            }
            Category::Place | Category::Rvalue(..) => {
                let operand = unpack!(block = this.as_temp(block, scope, expr, Mutability::Mut));
                block.and(Operand::Move(Place::from(operand)))
            }
        }
    }
}