[X86] Fix a couple lowering functions that called ReplaceAllUsesOfValueWith for the...

Returning SDValue() makes the caller think custom lowering was unsuccessful and then it will fall back to trying to expand the original node. This expanded code will end up with no users and end up being pruned later. But it was useless unnecessary work to create it.

Instead return a MERGE_VALUES with all the results so the caller knows something changed. The caller can handle the replacements.

For one of the cases I had to use UNDEF has a dummy value for a result we know is unused. This should get pruned later.

llvm-svn: 357935

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 4cc2bf4..6719931 100644 (file)
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -25756,10 +25756,8 @@ static SDValue LowerCMP_SWAP(SDValue Op, const X86Subtarget &Subtarget,
                                       MVT::i32, cpOut.getValue(2));
   SDValue Success = getSETCC(X86::COND_E, EFLAGS, DL, DAG);
 
-  DAG.ReplaceAllUsesOfValueWith(Op.getValue(0), cpOut);
-  DAG.ReplaceAllUsesOfValueWith(Op.getValue(1), Success);
-  DAG.ReplaceAllUsesOfValueWith(Op.getValue(2), EFLAGS.getValue(1));
-  return SDValue();
+  return DAG.getNode(ISD::MERGE_VALUES, DL, Op->getVTList(),
+                     cpOut, Success, EFLAGS.getValue(1));
 }
 
 // Create MOVMSKB, taking into account whether we need to split for AVX1.
@@ -26198,8 +26196,9 @@ static SDValue lowerAtomicArith(SDValue N, SelectionDAG &DAG,
   SDValue LockOp = lowerAtomicArithWithLOCK(N, DAG, Subtarget);
   // RAUW the chain, but don't worry about the result, as it's unused.
   assert(!N->hasAnyUseOfValue(0));
-  DAG.ReplaceAllUsesOfValueWith(N.getValue(1), LockOp.getValue(1));
-  return SDValue();
+  // NOTE: The getUNDEF is needed to give something for the unused result 0.
+  return DAG.getNode(ISD::MERGE_VALUES, DL, N->getVTList(),
+                     DAG.getUNDEF(VT), LockOp.getValue(1));
 }
 
 static SDValue LowerATOMIC_STORE(SDValue Op, SelectionDAG &DAG) {