Strip metadata when speculatively hoisting instructions

This is fix for PR24059.

When we are hoisting instruction above some condition it may turn out
that metadata on this instruction was control dependant on the condition.
This metadata becomes invalid and we need to drop it.

This patch should cover most obvious places of speculative execution (which
I have found by greping isSafeToSpeculativelyExecute). I think there are more
cases but at least this change covers the severe ones.

Differential Revision: http://reviews.llvm.org/D14398

llvm-svn: 252604

2 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index ba39afd4287..6d70cdc3ade 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -672,6 +672,10 @@ static bool hoist(Instruction &I, BasicBlock *Preheader) {
   // Move the new node to the Preheader, before its terminator.
   I.moveBefore(Preheader->getTerminator());
 
+  // Metadata can be dependent on the condition we are hoisting above.
+  // Conservatively strip all metadata on the instruction.
+  I.dropUnknownNonDebugMetadata();
+
   if (isa<LoadInst>(I)) ++NumMovedLoads;
   else if (isa<CallInst>(I)) ++NumMovedCalls;
   ++NumHoisted;
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index e0c598f92e2..ff81e7d5acf 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1618,6 +1618,11 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
     SpeculatedStore->setOperand(0, S);
   }
 
+  // Metadata can be dependent on the condition we are hoisting above.
+  // Conservatively strip all metadata on the instruction.
+  for (auto &I: *ThenBB)
+    I.dropUnknownNonDebugMetadata();
+
   // Hoist the instructions.
   BB->getInstList().splice(BI->getIterator(), ThenBB->getInstList(),
                            ThenBB->begin(), std::prev(ThenBB->end()));