[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

2 files changed, 49 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)) {
diff --git a/llvm/test/Transforms/InstCombine/load-combine-metadata.ll b/llvm/test/Transforms/InstCombine/load-combine-metadata.ll
new file mode 100644
index 00000000000..d67f83c1ebc
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/load-combine-metadata.ll
@@ -0,0 +1,31 @@
+; RUN: opt -instcombine -S < %s | FileCheck %s
+
+target datalayout = "e-m:e-p:64:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+; CHECK-LABEL: @test_load_load_combine_metadata(
+; Check that range metadata is combined and AA metadata is preserved
+; CHECK: %[[V:.*]] = load i32, i32* %0
+; CHECK-SAME: !tbaa !{{[0-9]+}}
+; CHECK-SAME: !range ![[RANGE:[0-9]+]]
+; CHECK-SAME: !alias.scope !{{[0-9]+}}
+; CHECK-SAME: !noalias !{{[0-9]+}}
+; CHECK: store i32 %[[V]], i32* %1
+; CHECK: store i32 %[[V]], i32* %2
+define void @test_load_load_combine_metadata(i32*, i32*, i32*) {
+  %a = load i32, i32* %0, !tbaa !8, !range !0, !alias.scope !5, !noalias !6
+  %b = load i32, i32* %0, !range !1
+  store i32 %a, i32* %1
+  store i32 %b, i32* %2
+  ret void
+}
+
+; CHECK: ![[RANGE]] = !{i32 0, i32 1, i32 8, i32 9}
+!0 = !{ i32 0, i32 1 }
+!1 = !{ i32 8, i32 9 }
+!2 = !{!2}
+!3 = !{!3, !2}
+!4 = !{!4, !2}
+!5 = !{!3}
+!6 = !{!4}
+!7 = !{ !"tbaa root" }
+!8 = !{ !7, !7, i64 0 }