[PowerPC] only check the load instruction result number 0

[shchenz]

Summary

this patch:
1: generates more reverse memory load operations, because now the transformation only bases on load instruction result number 0.
2: fixes an exposed bug related to the reverse memory load location. Without the load location fix, the fixed case would be like:

; CHECK:       # %bb.0:
; CHECK-NEXT:    stxv 34, 0(3)
; CHECK-NEXT:    lxvd2x 34, 0, 3
; CHECK-NEXT:    blr

[nemanjai]

LGTM. Thanks.

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

SDValue PPCTargetLowering::combineVReverseMemOP(ShuffleVectorSDNode *SVN,
   // It is conflict with PPCVSXSwapRemoval opt. So we don't do it.
   if (!Subtarget.hasP9Vector())
     return SDValue();
 
   if(!IsElementReverse(SVN))
     return SDValue();
 
   if (LSBase->getOpcode() == ISD::LOAD) {
-    // If the load has more than one user except the shufflevector instruction,
-    // it is not profitable to replace the shufflevector with a reverse load.
-    if (!LSBase->hasOneUse())
+    // If the load return value 0 has more than one user except the
+    // shufflevector instruction, it is not profitable to replace the
+    // shufflevector with a reverse load.
+    for (SDNode::use_iterator UI = LSBase->use_begin(), UE = LSBase->use_end();
+         UI != UE; ++UI)
+      if (UI.getUse().getResNo() == 0 && UI->getOpcode() != ISD::VECTOR_SHUFFLE)
         return SDValue();
 
-    SDLoc dl(SVN);
+    SDLoc dl(LSBase);
     SDValue LoadOps[] = {LSBase->getChain(), LSBase->getBasePtr()};
     return DAG.getMemIntrinsicNode(
         PPCISD::LOAD_VEC_BE, dl, DAG.getVTList(VT, MVT::Other), LoadOps,
         LSBase->getMemoryVT(), LSBase->getMemOperand());
   }
 
   if (LSBase->getOpcode() == ISD::STORE) {
     // If there are other uses of the shuffle, the swap cannot be avoided.

llvm/test/CodeGen/PowerPC/vsx-shuffle-le-load.ll

 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
 ; RUN: llc -verify-machineinstrs -mcpu=pwr9 -mattr=+vsx \
 ; RUN:   -mtriple=powerpc64le-unknown-linux-gnu < %s | FileCheck %s
 
 define <2 x double> @loadChainHasUser(<2 x double>* %p1, <2 x double> %v2) {
 ; CHECK-LABEL: loadChainHasUser:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    lxv 0, 0(3)
+; CHECK-NEXT:    lxvd2x 0, 0, 3
 ; CHECK-NEXT:    stxv 34, 0(3)
-; CHECK-NEXT:    xxswapd 34, 0
+; CHECK-NEXT:    xxlor 34, 0, 0
 ; CHECK-NEXT:    blr
   %v1 = load <2 x double>, <2 x double>* %p1
   store <2 x double> %v2, <2 x double>* %p1, align 16
   %v3 = shufflevector <2 x double> %v1, <2 x double> %v1, <2 x i32> < i32 1, i32 0>
   ret <2 x double> %v3
 }