Memory Dependence Analysis (not mem-dep test) take advantage of "invariant.load" metadata.

The "invariant.load" metadata indicates the memory unit being accessed is immutable.
A load annotated with this metadata can be moved across any store.

As I am not sure if it is legal to move such loads across barrier/fence, this
change dose not allow such transformation.

rdar://11311484

Thank Arnold for code review.

llvm-svn: 176562

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/IR/LLVMContext.cpp b/llvm/lib/IR/LLVMContext.cpp
index b73cd03ddd6..883bb9878fa 100644
--- a/llvm/lib/IR/LLVMContext.cpp
+++ b/llvm/lib/IR/LLVMContext.cpp
@@ -58,6 +58,11 @@ LLVMContext::LLVMContext() : pImpl(new LLVMContextImpl(*this)) {
   unsigned TBAAStructID = getMDKindID("tbaa.struct");
   assert(TBAAStructID == MD_tbaa_struct && "tbaa.struct kind id drifted");
   (void)TBAAStructID;
+
+  // Create the 'invariant.load' metadata kind.
+  unsigned InvariantLdId = getMDKindID("invariant.load");
+  assert(InvariantLdId == MD_invariant_load && "invariant.load kind id drifted");
+  (void)InvariantLdId;
 }
 LLVMContext::~LLVMContext() { delete pImpl; }