SimplifyCFG: Avoid miscompilations due to removed lifetime intrinsics.

The lifetime intrinsics need some work in order to make it clear which
optimizations are or are not valid.

For now dropping this optimization avoids a miscompilation.

Patch by Björn Steinbrink.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214336 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 24bb63bb60a5f8108bb1006db1715dfea44a7214..1c62559739f9bd34c7e5b73fe36510cdd3f561ce 100644 (file)
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -4008,7 +4008,7 @@ bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
     return true;
 
   // If the Terminator is the only non-phi instruction, simplify the block.
-  BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime();
+  BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
   if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
       TryToSimplifyUncondBranchFromEmptyBlock(BB))
     return true;

diff --git a/test/Transforms/SimplifyCFG/lifetime.ll b/test/Transforms/SimplifyCFG/lifetime.ll
index b79422172530ed65afe88585fce53f8bf01827f4..7c66be5295007daa64cae3715a31fe3514d3b8fd 100644 (file)
--- a/test/Transforms/SimplifyCFG/lifetime.ll
+++ b/test/Transforms/SimplifyCFG/lifetime.ll
@@ -1,11 +1,11 @@
 ; RUN: opt < %s -simplifycfg -S | FileCheck %s
 
-; Test that a lifetime intrinsic doesn't prevent us from simplifying this.
+; Test that a lifetime intrinsic isn't removed because that would change semantics
 
 ; CHECK: foo
 ; CHECK: entry:
-; CHECK-NOT: bb0:
-; CHECK-NOT: bb1:
+; CHECK: bb0:
+; CHECK: bb1:
 ; CHECK: ret
 define void @foo(i1 %x) {
 entry: