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PR9420; an instruction before an unreachable is guaranteed not to have any

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reachable uses, but there still might be uses in dead blocks.  Use the
standard solution of replacing all the uses with undef.  This is
a rare case because it's very sensitive to phase ordering in SimplifyCFG.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127299 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eli Friedman 2011-03-09 00:48:33 +00:00
parent e11128dd9d
commit 2adc5b6a17
2 changed files with 34 additions and 1 deletions
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4
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -2168,7 +2168,9 @@ bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
if (LI->isVolatile())
break;
// Delete this instruction
// Delete this instruction (any uses are guaranteed to be dead)
if (!BBI->use_empty())
BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
BBI->eraseFromParent();
Changed = true;
}

31
test/Transforms/SimplifyCFG/2011-03-08-UnreachableUse.ll Normal file
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@ -0,0 +1,31 @@
; RUN: opt < %s -simplifycfg -S | FileCheck %s
; PR9420
; Note that the crash in PR9420 test is sensitive to the ordering of
; the transformations done by SimplifyCFG, so this test is likely to rot
; quickly.
define noalias i8* @func_29() nounwind {
; CHECK: entry:
; CHECK-NEXT: unreachable
entry:
br label %for.cond
for.cond: ; preds = %for.inc38, %entry
%p_34.addr.0 = phi i16 [ 1, %entry ], [ %conv40, %for.inc38 ]
br label %for.cond1
for.cond1: ; preds = %for.inc29, %for.cond
%p_32.addr.0 = phi i1 [ true, %for.cond ], [ true, %for.inc29 ]
br i1 %p_32.addr.0, label %for.body8, label %for.inc38
for.body8: ; preds = %for.cond1
unreachable
for.inc29: ; preds = %for.cond17
br label %for.cond1
for.inc38: ; preds = %for.end32
%conv40 = add i16 %p_34.addr.0, 1
br label %for.cond
}