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[InstCombine] Fix worklist management in return combine

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There are two related bugs here: First, we don't add the operand
we're replacing to the worklist, which means it may not get DCEd
(see test change). Second, usually this would just get picked up
in the next iteration, but we also do not report the instruction
as changed. This means that we do not get that extra instcombine
iteration, and more importantly, may break the pass pipeline, as
the function is not marked as changed.

Differential Revision: https://reviews.llvm.org/D72864
This commit is contained in:
Nikita Popov 2020-01-16 21:38:19 +01:00
parent d31158ae0f
commit 50ac6afd84
2 changed files with 9 additions and 12 deletions
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7
lib/Transforms/InstCombine/InstructionCombining.cpp
View File

@ -2592,14 +2592,17 @@ Instruction *InstCombiner::visitReturnInst(ReturnInst &RI) {
Value *ResultOp = RI.getOperand(0);
Type *VTy = ResultOp->getType();
if (!VTy->isIntegerTy())
if (!VTy->isIntegerTy() || isa<Constant>(ResultOp))
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())
if (Known.isConstant()) {
Worklist.AddValue(ResultOp);
RI.setOperand(0, Constant::getIntegerValue(VTy, Known.getConstant()));
return &RI;
}
return nullptr;
}

14
test/Transforms/InstCombine/assume.ll
View File

@ -190,16 +190,10 @@ entry:
}
define i32 @icmp1(i32 %a) #0 {
; EXPENSIVE-ON-LABEL: @icmp1(
; EXPENSIVE-ON-NEXT: [[CMP:%.*]] = icmp sgt i32 [[A:%.*]], 5
; EXPENSIVE-ON-NEXT: tail call void @llvm.assume(i1 [[CMP]])
; EXPENSIVE-ON-NEXT: ret i32 1
;
; EXPENSIVE-OFF-LABEL: @icmp1(
; EXPENSIVE-OFF-NEXT: [[CMP:%.*]] = icmp sgt i32 [[A:%.*]], 5
; EXPENSIVE-OFF-NEXT: tail call void @llvm.assume(i1 [[CMP]])
; EXPENSIVE-OFF-NEXT: [[CONV:%.*]] = zext i1 [[CMP]] to i32
; EXPENSIVE-OFF-NEXT: ret i32 1
; CHECK-LABEL: @icmp1(
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i32 [[A:%.*]], 5
; CHECK-NEXT: tail call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: ret i32 1
;
%cmp = icmp sgt i32 %a, 5
tail call void @llvm.assume(i1 %cmp)