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Sink: Handle instruction sink when a user is dead

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Summary:
  The current instruction sink pass uses findNearestCommonDominator of all users to find block to sink the instruction to.
However, a user may be in a dead block, which will result in unexpected behavior.

This patch handles such cases by skipping dead blocks. This patch fixes:
https://bugs.llvm.org/show_bug.cgi?id=47415

Reviewers:
  MaskRay, arsenm

Differential Revision:
  https://reviews.llvm.org/D89166
This commit is contained in:
Changpeng Fang 2020-10-09 16:20:26 -07:00
parent 3755e8a85b
commit 7c619d4ea7
2 changed files with 45 additions and 0 deletions
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3
lib/Transforms/Scalar/Sink.cpp
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@ -135,6 +135,9 @@ static bool SinkInstruction(Instruction *Inst,
for (Use &U : Inst->uses()) {
Instruction *UseInst = cast<Instruction>(U.getUser());
BasicBlock *UseBlock = UseInst->getParent();
// Don't worry about dead users.
if (!DT.isReachableFromEntry(UseBlock))
continue;
if (PHINode *PN = dyn_cast<PHINode>(UseInst)) {
// PHI nodes use the operand in the predecessor block, not the block with
// the PHI.

42
test/Transforms/Sink/dead-user.ll Normal file
View File

@ -0,0 +1,42 @@
; Compiler should not be broken with a dead user.
; RUN: opt -sink -S < %s | FileCheck %s
; CHECK-LABEL: @test(
; CHECK: bb.0:
; CHECK-NEXT: %conv = sext i16 %p1 to i32
; CHECK-NEXT: br i1 undef, label %bb.1, label %bb.3
; CHECK: bb.1: ; preds = %bb.0
; CHECK-NEXT: br label %bb.2
; CHECK: bb.2: ; preds = %bb.2, %bb.1
; CHECK-NEXT: %and.2 = and i32 undef, %conv
; CHECK-NEXT: br label %bb.2
; CHECK: bb.3: ; preds = %bb.3, %bb.0
; CHECK-NEXT: %and.3 = and i32 undef, %conv
; CHECK-NEXT: br label %bb.3
; CHECK: dead: ; preds = %dead
; CHECK-NEXT: %and.dead = and i32 undef, %conv
; CHECK-NEXT: br label %dead
define void @test(i16 %p1) {
bb.0:
%conv = sext i16 %p1 to i32
br i1 undef, label %bb.1, label %bb.3
bb.1: ; preds = %bb.0
br label %bb.2
bb.2: ; preds = %bb.2, %bb.1
%and.2 = and i32 undef, %conv
br label %bb.2
bb.3: ; preds = %bb.3, %bb.0
%and.3 = and i32 undef, %conv
br label %bb.3
dead: ; preds = %dead
%and.dead = and i32 undef, %conv
br label %dead
}