[InstCombine] Properly combine metadata when replacing a load with another

Not doing this can lead to misoptimizations down the line, e.g. because
of range metadata on the replacing load excluding values that are valid
for the load that is being replaced.

llvm-svn: 241886

1 files changed, 18 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index e7a45330d95..224e3321926 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -749,10 +749,27 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
   // where there are several consecutive memory accesses to the same location,
   // separated by a few arithmetic operations.
   BasicBlock::iterator BBI = &LI;
-  if (Value *AvailableVal = FindAvailableLoadedValue(Op, LI.getParent(), BBI,6))
+  AAMDNodes AATags;
+  if (Value *AvailableVal = FindAvailableLoadedValue(Op, LI.getParent(), BBI,
+                                                     6, nullptr, &AATags)) {
+    if (LoadInst *NLI = dyn_cast<LoadInst>(AvailableVal)) {
+      unsigned KnownIDs[] = {
+        LLVMContext::MD_tbaa,
+        LLVMContext::MD_alias_scope,
+        LLVMContext::MD_noalias,
+        LLVMContext::MD_range,
+        LLVMContext::MD_invariant_load,
+        LLVMContext::MD_nonnull,
+      };
+      combineMetadata(NLI, &LI, KnownIDs);
+      if (AATags)
+        NLI->setAAMetadata(AATags);
+    };
+
     return ReplaceInstUsesWith(
         LI, Builder->CreateBitOrPointerCast(AvailableVal, LI.getType(),
                                             LI.getName() + ".cast"));
+  }
 
   // load(gep null, ...) -> unreachable
   if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Op)) {