[X86] Move some hasOneUse checks after checking what the opcode is.

[craig.topper]

Summary

Calling hasOneUse can be expensive on nodes with multiple results.
Especially when some results are Chains. By checking the opcode first,
we can avoid walking the uses if it isn't an interesting node,
and thus avoid calling hasOneUse on a node that might have many uses.

Found by profiling the IR given in D123857.

[pengfei]

we can know avoid walking the uses if it isn't an interesting node

Should 'know' be 'now'?

[RKSimon]

LGTM - with one minor

llvm/lib/Target/X86/X86ISelLowering.cpp

48905

I guess you can test the isNullConstant first ?

llvm/lib/Target/X86/X86ISelLowering.cpp

if (!St->isTruncatingStore() && VT == MVT::v16i8 && !Subtarget.hasBWI() &&
       St->getValue().hasOneUse() && !DCI.isBeforeLegalizeOps()) {
     SDValue Ext = DAG.getNode(ISD::ANY_EXTEND, dl, MVT::v16i32,
                               St->getValue().getOperand(0));
     return DAG.getTruncStore(St->getChain(), dl, Ext, St->getBasePtr(),
                              MVT::v16i8, St->getMemOperand());
   }
 
   // Try to fold a VTRUNCUS or VTRUNCS into a truncating store.
-  if (!St->isTruncatingStore() && StoredVal.hasOneUse() &&
+  if (!St->isTruncatingStore() &&
       (StoredVal.getOpcode() == X86ISD::VTRUNCUS ||
        StoredVal.getOpcode() == X86ISD::VTRUNCS) &&
+      StoredVal.hasOneUse() &&
       TLI.isTruncStoreLegal(StoredVal.getOperand(0).getValueType(), VT)) {
     bool IsSigned = StoredVal.getOpcode() == X86ISD::VTRUNCS;
     return EmitTruncSStore(IsSigned, St->getChain(),
                            dl, StoredVal.getOperand(0), St->getBasePtr(),
                            VT, St->getMemOperand(), DAG);
   }
 
   // Try to fold a extract_element(VTRUNC) pattern into a truncating store.
-  if (!St->isTruncatingStore() && StoredVal.hasOneUse()) {
+  if (!St->isTruncatingStore()) {
     auto IsExtractedElement = [](SDValue V) {
-      if (V.getOpcode() == ISD::TRUNCATE && V.getOperand(0).hasOneUse())
+      if (V.getOpcode() == ISD::TRUNCATE && V.hasOneUse())
         V = V.getOperand(0);
       unsigned Opc = V.getOpcode();
-      if (Opc == ISD::EXTRACT_VECTOR_ELT || Opc == X86ISD::PEXTRW) {
-        if (V.getOperand(0).hasOneUse() && isNullConstant(V.getOperand(1)))
-          return V.getOperand(0);
-      }
+      if ((Opc == ISD::EXTRACT_VECTOR_ELT || Opc == X86ISD::PEXTRW) &&
+          isNullConstant(V.getOperand(1)) && V.hasOneUse() &&
+          V.getOperand(0).hasOneUse())
       return SDValue();
     };
     if (SDValue Extract = IsExtractedElement(StoredVal)) {
       SDValue Trunc = peekThroughOneUseBitcasts(Extract);
       if (Trunc.getOpcode() == X86ISD::VTRUNC) {
         SDValue Src = Trunc.getOperand(0);
         MVT DstVT = Trunc.getSimpleValueType();
         MVT SrcVT = Src.getSimpleValueType();