AVX512: Fix LowerMSCATTER() return value.

[igorb]

Summary

AVX512: Fix LowerMSCATTER() return value.
Bug description:
The bug was discovered when test was compiled with -O0.
In case scatter result is DAG root , VectorLegalizer failed (assert) due to LowerMSCATTER() return kmask as result.
Change LowerMSCATTER() to return chain as original node do.

[delena]

LGTM

llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

static SDValue LowerMSCATTER(SDValue Op, const X86Subtarget &Subtarget,
   Mask = DAG.getNode(ISD::TRUNCATE, dl, BitMaskVT, Mask);
 
   // The mask is killed by scatter, add it to the values
   SDVTList VTs = DAG.getVTList(BitMaskVT, MVT::Other);
   SDValue Ops[] = {Chain, Src, Mask, BasePtr, Index};
   NewScatter = DAG.getMaskedScatter(VTs, N->getMemoryVT(), dl, Ops,
                                     N->getMemOperand());
   DAG.ReplaceAllUsesWith(Op, SDValue(NewScatter.getNode(), 1));
-  return SDValue(NewScatter.getNode(), 0);
+  return SDValue(NewScatter.getNode(), 1);
 }
 
 static SDValue LowerMLOAD(SDValue Op, const X86Subtarget &Subtarget,
                           SelectionDAG &DAG) {
 
   MaskedLoadSDNode *N = cast<MaskedLoadSDNode>(Op.getNode());
   MVT VT = Op.getSimpleValueType();
   SDValue Mask = N->getMask();

llvm/trunk/test/CodeGen/X86/masked_gather_scatter.ll

 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
 ; RUN: llc -mtriple=x86_64-unknown-linux-gnu  -mattr=+avx512f < %s | FileCheck %s --check-prefix=KNL_64
 ; RUN: llc -mtriple=i386-unknown-linux-gnu  -mattr=+avx512f < %s | FileCheck %s --check-prefix=KNL_32
 ; RUN: llc -mtriple=x86_64-unknown-linux-gnu  -mattr=+avx512vl -mattr=+avx512dq < %s | FileCheck %s --check-prefix=SKX
 ; RUN: llc -mtriple=i386-unknown-linux-gnu  -mattr=+avx512vl -mattr=+avx512dq < %s | FileCheck %s --check-prefix=SKX_32
 ; RUN: opt -mtriple=x86_64-apple-darwin -codegenprepare -mcpu=corei7-avx -S < %s | FileCheck %s -check-prefix=SCALAR
-
+; RUN: llc -O0 -mtriple=x86_64-unknown-linux-gnu -mcpu=skx < %s -o /dev/null
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 
 ; SCALAR-LABEL: test1
 ; SCALAR:      extractelement <16 x float*>
 ; SCALAR-NEXT: load float