GVN: Preserve invariant.load metadata

If both instructions to be replaced are marked invariant the resulting
instruction is invariant.

rdar://13358910

Fix by Erik Eckstein!

llvm-svn: 211801

diff --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp
index 56781d4..106eba0 100644 (file)
--- a/llvm/lib/Transforms/Scalar/GVN.cpp
+++ b/llvm/lib/Transforms/Scalar/GVN.cpp
@@ -1798,6 +1798,10 @@ static void patchReplacementInstruction(Instruction *I, Value *Repl) {
       case LLVMContext::MD_fpmath:
         ReplInst->setMetadata(Kind, MDNode::getMostGenericFPMath(IMD, ReplMD));
         break;
+      case LLVMContext::MD_invariant_load:
+        // Only set the !invariant.load if it is present in both instructions.
+        ReplInst->setMetadata(Kind, IMD);
+        break;
       }
     }
   }

diff --git a/llvm/test/Transforms/GVN/invariant-load.ll b/llvm/test/Transforms/GVN/invariant-load.ll
new file mode 100644 (file)
index 0000000..73a1278
--- /dev/null
+++ b/llvm/test/Transforms/GVN/invariant-load.ll
@@ -0,0 +1,30 @@
+; RUN: opt -basicaa -gvn -S < %s | FileCheck %s
+
+define i32 @test1(i32* nocapture %p, i8* nocapture %q) {
+; CHECK-LABEL: test1
+; CHECK: %x = load i32* %p, align 4, !invariant.load !0
+; CHECK-NOT: %y = load
+entry:
+  %x = load i32* %p, align 4, !invariant.load !0
+  %conv = trunc i32 %x to i8
+  store i8 %conv, i8* %q, align 1
+  %y = load i32* %p, align 4, !invariant.load !0
+  %add = add i32 %y, 1
+  ret i32 %add
+}
+
+define i32 @test2(i32* nocapture %p, i8* nocapture %q) {
+; CHECK-LABEL: test2
+; CHECK-NOT: !invariant.load
+; CHECK-NOT: %y = load
+entry:
+  %x = load i32* %p, align 4
+  %conv = trunc i32 %x to i8
+  store i8 %conv, i8* %q, align 1
+  %y = load i32* %p, align 4, !invariant.load !0
+  %add = add i32 %y, 1
+  ret i32 %add
+}
+
+!0 = metadata !{ }
+