Fix pr14893.

When simplifycfg moves an instruction, it must drop metadata it doesn't know
is still valid with the preconditions changes. In particular, it must drop
the range and tbaa metadata.

The patch implements this with an utility function to drop all metadata not
in a white list.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200322 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 0401b9a7f7..effc08edaa 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2154,6 +2154,14 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
     Instruction *NewBonus = 0;
     if (BonusInst) {
       NewBonus = BonusInst->clone();
+
+      // If we moved a load, we cannot any longer claim any knowledge about
+      // its potential value. The previous information might have been valid
+      // only given the branch precondition.
+      // For an analogous reason, we must also drop all the metadata whose
+      // semantics we don't understand.
+      NewBonus->dropUnknownMetadata(LLVMContext::MD_dbg);
+
       PredBlock->getInstList().insert(PBI, NewBonus);
       NewBonus->takeName(BonusInst);
       BonusInst->setName(BonusInst->getName()+".old");