[Transforms] move copying of load metadata to helper function; NFC

There's another proposed load combine that can make use of this code
in D64432.

llvm-svn: 366949

1 files changed, 51 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 8e50172..1605ec5 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -2390,6 +2390,57 @@ void llvm::combineMetadataForCSE(Instruction *K, const Instruction *J,
   combineMetadata(K, J, KnownIDs, KDominatesJ);
 }
 
+void llvm::copyMetadataForLoad(LoadInst &Dest, const LoadInst &Source) {
+  SmallVector<std::pair<unsigned, MDNode *>, 8> MD;
+  Source.getAllMetadata(MD);
+  MDBuilder MDB(Dest.getContext());
+  Type *NewType = Dest.getType();
+  const DataLayout &DL = Source.getModule()->getDataLayout();
+  for (const auto &MDPair : MD) {
+    unsigned ID = MDPair.first;
+    MDNode *N = MDPair.second;
+    // Note, essentially every kind of metadata should be preserved here! This
+    // routine is supposed to clone a load instruction changing *only its type*.
+    // The only metadata it makes sense to drop is metadata which is invalidated
+    // when the pointer type changes. This should essentially never be the case
+    // in LLVM, but we explicitly switch over only known metadata to be
+    // conservatively correct. If you are adding metadata to LLVM which pertains
+    // to loads, you almost certainly want to add it here.
+    switch (ID) {
+    case LLVMContext::MD_dbg:
+    case LLVMContext::MD_tbaa:
+    case LLVMContext::MD_prof:
+    case LLVMContext::MD_fpmath:
+    case LLVMContext::MD_tbaa_struct:
+    case LLVMContext::MD_invariant_load:
+    case LLVMContext::MD_alias_scope:
+    case LLVMContext::MD_noalias:
+    case LLVMContext::MD_nontemporal:
+    case LLVMContext::MD_mem_parallel_loop_access:
+    case LLVMContext::MD_access_group:
+      // All of these directly apply.
+      Dest.setMetadata(ID, N);
+      break;
+
+    case LLVMContext::MD_nonnull:
+      copyNonnullMetadata(Source, N, Dest);
+      break;
+
+    case LLVMContext::MD_align:
+    case LLVMContext::MD_dereferenceable:
+    case LLVMContext::MD_dereferenceable_or_null:
+      // These only directly apply if the new type is also a pointer.
+      if (NewType->isPointerTy())
+        Dest.setMetadata(ID, N);
+      break;
+
+    case LLVMContext::MD_range:
+      copyRangeMetadata(DL, Source, N, Dest);
+      break;
+    }
+  }
+}
+
 void llvm::patchReplacementInstruction(Instruction *I, Value *Repl) {
   auto *ReplInst = dyn_cast<Instruction>(Repl);
   if (!ReplInst)