[llvm] r307184 - {DAGCombiner] Fold (rot x, 0) -> x

[Simon Pilgrim via llvm-commits]

Author: rksimon
Date: Wed Jul  5 11:27:11 2017
New Revision: 307184

URL: http://llvm.org/viewvc/llvm-project?rev=307184&view=rev
Log:
{DAGCombiner] Fold (rot x, 0) -> x

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    llvm/trunk/test/CodeGen/X86/combine-rotates.ll

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=307184&r1=307183&r2=307184&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Wed Jul  5 11:27:11 2017
@@ -5273,6 +5273,10 @@ SDValue DAGCombiner::visitRotate(SDNode
   SDValue N1 = N->getOperand(1);
   EVT VT = N->getValueType(0);
 
+  // fold (rot x, 0) -> x
+  if (isNullConstantOrNullSplatConstant(N1))
+    return N0;
+
   // fold (rot* x, (trunc (and y, c))) -> (rot* x, (and (trunc y), (trunc c))).
   if (N1.getOpcode() == ISD::TRUNCATE &&
       N1.getOperand(0).getOpcode() == ISD::AND) {

Modified: llvm/trunk/test/CodeGen/X86/combine-rotates.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/combine-rotates.ll?rev=307184&r1=307183&r2=307184&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/combine-rotates.ll (original)
+++ llvm/trunk/test/CodeGen/X86/combine-rotates.ll Wed Jul  5 11:27:11 2017
@@ -59,7 +59,6 @@ define <4 x i32> @combine_vec_rot_rot_sp
 define <4 x i32> @combine_vec_rot_rot_splat_zero(<4 x i32> %x) {
 ; XOP-LABEL: combine_vec_rot_rot_splat_zero:
 ; XOP:       # BB#0:
-; XOP-NEXT:    vprotd $0, %xmm0, %xmm0
 ; XOP-NEXT:    retq
 ;
 ; AVX512-LABEL: combine_vec_rot_rot_splat_zero: