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GVN: If a branch has two identical successors, we cannot declare either dead.

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This previously caused miscompilations as a result of phi nodes receiving
undef incoming values from blocks dominated by such successors.

Differential Revision: http://reviews.llvm.org/D10726

llvm-svn: 240670
This commit is contained in:
Peter Collingbourne 2015-06-25 18:32:02 +00:00
parent 393725d952
commit 3b0fac198c
2 changed files with 42 additions and 0 deletions
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4
lib/Transforms/Scalar/GVN.cpp
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@ -2804,6 +2804,10 @@ bool GVN::processFoldableCondBr(BranchInst *BI) {
if (!BI || BI->isUnconditional())
return false;
// If a branch has two identical successors, we cannot declare either dead.
if (BI->getSuccessor(0) == BI->getSuccessor(1))
return false;
ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition());
if (!Cond)
return false;

38
test/Transforms/GVN/br-identical.ll Normal file
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@ -0,0 +1,38 @@
; RUN: opt -gvn -S -o - %s | FileCheck %s
; If a branch has two identical successors, we cannot declare either dead.
define void @widget(i1 %p) {
entry:
br label %bb2
bb2:
%t1 = phi i64 [ 0, %entry ], [ %t5, %bb7 ]
%t2 = add i64 %t1, 1
%t3 = icmp ult i64 0, %t2
br i1 %t3, label %bb3, label %bb4
bb3:
%t4 = call i64 @f()
br label %bb4
bb4:
; CHECK-NOT: phi {{.*}} undef
%foo = phi i64 [ %t4, %bb3 ], [ 0, %bb2 ]
br i1 %p, label %bb5, label %bb6
bb5:
br i1 true, label %bb7, label %bb7
bb6:
br i1 true, label %bb7, label %bb7
bb7:
%t5 = add i64 %t1, 1
br i1 %p, label %bb2, label %bb8
bb8:
ret void
}
declare i64 @f()