bjoernager/rust
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Auto merge of #86107 - Smittyvb:peephole-optim-eq-bool, r=wesleywiser

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Peephole optimize `x == false` and `x != true`

This adds peephole optimizations to make `x == false`, `false == x`, `x != true`, and `true != x` get optimized to `!x` in the `instcombine` MIR pass. That pass currently handles `x == true` -> `x` already.
This commit is contained in:
bors 2021-06-09 06:06:06 +00:00
commit d45d205d59
6 changed files with 180 additions and 7 deletions
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21
compiler/rustc_mir/src/transform/instcombine.rs
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@ -4,7 +4,7 @@ use crate::transform::MirPass;
use rustc_hir::Mutability;
use rustc_middle::mir::{
BinOp, Body, Constant, LocalDecls, Operand, Place, ProjectionElem, Rvalue, SourceInfo,
StatementKind,
StatementKind, UnOp,
};
use rustc_middle::ty::{self, TyCtxt};
@ -47,28 +47,35 @@ impl<'tcx, 'a> InstCombineContext<'tcx, 'a> {
Rvalue::BinaryOp(op @ (BinOp::Eq | BinOp::Ne), box (a, b)) => {
let new = match (op, self.try_eval_bool(a), self.try_eval_bool(b)) {
// Transform "Eq(a, true)" ==> "a"
(BinOp::Eq, _, Some(true)) => Some(a.clone()),
(BinOp::Eq, _, Some(true)) => Some(Rvalue::Use(a.clone())),
// Transform "Ne(a, false)" ==> "a"
(BinOp::Ne, _, Some(false)) => Some(a.clone()),
(BinOp::Ne, _, Some(false)) => Some(Rvalue::Use(a.clone())),
// Transform "Eq(true, b)" ==> "b"
(BinOp::Eq, Some(true), _) => Some(b.clone()),
(BinOp::Eq, Some(true), _) => Some(Rvalue::Use(b.clone())),
// Transform "Ne(false, b)" ==> "b"
(BinOp::Ne, Some(false), _) => Some(b.clone()),
(BinOp::Ne, Some(false), _) => Some(Rvalue::Use(b.clone())),
// FIXME: Consider combining remaining comparisons into logical operations:
// Transform "Eq(false, b)" ==> "Not(b)"
(BinOp::Eq, Some(false), _) => Some(Rvalue::UnaryOp(UnOp::Not, b.clone())),
// Transform "Ne(true, b)" ==> "Not(b)"
(BinOp::Ne, Some(true), _) => Some(Rvalue::UnaryOp(UnOp::Not, b.clone())),
// Transform "Eq(a, false)" ==> "Not(a)"
(BinOp::Eq, _, Some(false)) => Some(Rvalue::UnaryOp(UnOp::Not, a.clone())),
// Transform "Ne(a, true)" ==> "Not(a)"
(BinOp::Ne, _, Some(true)) => Some(Rvalue::UnaryOp(UnOp::Not, a.clone())),
_ => None,
};
if let Some(new) = new {
if self.should_combine(source_info, rvalue) {
*rvalue = Rvalue::Use(new);
*rvalue = new;
}
}
}