[CodeGen] Fix hashing for MO_ExternalSymbol MachineOperands.

We were hashing the string pointer, not the string, so two instructions
could be identical (isIdenticalTo), but have different hash codes.

This showed up as a very rare, non-deterministic assertion failure
rehashing a DenseMap constructed by MachineOutliner.  So there's no
"real" testcase, just a unittest which checks that the hash function
behaves correctly.

I'm a little scared fixing this is going to cause a regression in
outlining or MachineCSE, but hopefully we won't run into any issues.

Differential Revision: https://reviews.llvm.org/D61975

llvm-svn: 362281

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/MachineOperand.cpp b/llvm/lib/CodeGen/MachineOperand.cpp
index a83459e..9458745 100644
--- a/llvm/lib/CodeGen/MachineOperand.cpp
+++ b/llvm/lib/CodeGen/MachineOperand.cpp
@@ -361,7 +361,7 @@ hash_code llvm::hash_value(const MachineOperand &MO) {
     return hash_combine(MO.getType(), MO.getTargetFlags(), MO.getIndex());
   case MachineOperand::MO_ExternalSymbol:
     return hash_combine(MO.getType(), MO.getTargetFlags(), MO.getOffset(),
-                        MO.getSymbolName());
+                        StringRef(MO.getSymbolName()));
   case MachineOperand::MO_GlobalAddress:
     return hash_combine(MO.getType(), MO.getTargetFlags(), MO.getGlobal(),
                         MO.getOffset());