Slightly generalize transformation of memmove(a,a,n) so that it also applies

to memcpy. (Such a memcpy is technically illegal, but in practice is safe
and is generated by struct self-assignment in C code.)

llvm-svn: 91621

2 files changed, 13 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index b9c536fe1e5..c7359c4de76 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -9896,9 +9896,11 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
                         Intrinsic::getDeclaration(M, MemCpyID, Tys, 1));
           Changed = true;
         }
+    }
 
+    if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) {
       // memmove(x,x,size) -> noop.
-      if (MMI->getSource() == MMI->getDest())
+      if (MTI->getSource() == MTI->getDest())
         return EraseInstFromFunction(CI);
     }
 
diff --git a/llvm/test/Transforms/InstCombine/memcpy.ll b/llvm/test/Transforms/InstCombine/memcpy.ll
new file mode 100644
index 00000000000..2e7b2c0bb41
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/memcpy.ll
@@ -0,0 +1,10 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+declare void @llvm.memcpy.i32(i8*, i8*, i32, i32)
+
+define void @test4(i8* %a) {
+        tail call void @llvm.memcpy.i32( i8* %a, i8* %a, i32 100, i32 1 )
+        ret void
+}
+; CHECK: define void @test4
+; CHECK-NEXT: ret void