[DAGCombine] Extend combineCarryDiamond()

[chfast]

Summary

In combineCarryDiamond() use getAsCarry() to find more candidates for being a carry flag.

[RKSimon]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

3157–3159

Do we need this change to get the codegen diff? Or is it just from the getAsCarry? If so we probably want to split the changes for clarity - one as cleanup and the other as improvement?

[RKSimon]

@chfast You might want to check D57317 to see if there's anything you can reuse

[chfast]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

3157–3159

The usage of isOperandOf is only esthetics. I should commit it separately. Does it need another review?

[RKSimon]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

3157–3159

No, a pre-commit is fine - then rebase this patch.

[RKSimon]

@chfast reverse ping?

[chfast]

Rebased.

[RKSimon]

LGTM - cheers

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

 //
 // And generate ADDCARRY (or SUBCARRY) with two result values:
 //
 //    {AddCarrySum, CarryOut} = (addcarry A, B, CarryIn)
 //
 // Our goal is to identify A, B, and CarryIn and produce ADDCARRY/SUBCARRY with
 // a single path for carry/borrow out propagation:
 static SDValue combineCarryDiamond(SelectionDAG &DAG, const TargetLowering &TLI,
-                                   SDValue Carry0, SDValue Carry1, SDNode *N) {
-  if (Carry0.getResNo() != 1 || Carry1.getResNo() != 1)
+                                   SDValue N0, SDValue N1, SDNode *N) {
+  SDValue Carry0 = getAsCarry(TLI, N0);
+  if (!Carry0)
     return SDValue();
+  SDValue Carry1 = getAsCarry(TLI, N1);
+  if (!Carry1)
+    return SDValue();
+
   unsigned Opcode = Carry0.getOpcode();
   if (Opcode != Carry1.getOpcode())
     return SDValue();
   if (Opcode != ISD::UADDO && Opcode != ISD::USUBO)
     return SDValue();
 
   // Canonicalize the add/sub of A and B (the top node in the above ASCII art)
   // as Carry0 and the add/sub of the carry in as Carry1 (the middle node).
   if (Carry1.getNode()->isOperandOf(Carry0.getNode()))
     std::swap(Carry0, Carry1);
 
   // Check if nodes are connected in expected way.
   if (Carry1.getOperand(0) != Carry0.getValue(0) &&
       Carry1.getOperand(1) != Carry0.getValue(0))
     return SDValue();
 
   // The carry in value must be on the righthand side for subtraction.
   unsigned CarryInOperandNum =
       Carry1.getOperand(0) == Carry0.getValue(0) ? 1 : 0;
   if (Opcode == ISD::USUBO && CarryInOperandNum != 1)

llvm/test/CodeGen/X86/addcarry.ll

; CHECK-NEXT:    retq
   ret { i64, i64, i1 } %r
 }
 
 ; basic test for combineCarryDiamond() with carries behind zext/and/trunc
 define { i64, i64, i1 } @addcarry_hidden_2x64(i64 %x0, i64 %x1, i64 %y0, i64 %y1) nounwind {
 ; CHECK-LABEL: addcarry_hidden_2x64:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    movq %rdi, %rax
-; CHECK-NEXT:    addq %rcx, %rsi
-; CHECK-NEXT:    setb %dil
 ; CHECK-NEXT:    addq %rdx, %rax
-; CHECK-NEXT:    adcq $0, %rsi
+; CHECK-NEXT:    adcq %rcx, %rsi
 ; CHECK-NEXT:    setb %cl
-; CHECK-NEXT:    orb %dil, %cl
 ; CHECK-NEXT:    movq %rsi, %rdx
 ; CHECK-NEXT:    retq
   %t0 = call { i64, i1 } @llvm.uadd.with.overflow.i64(i64 %x0, i64 %y0)
   %s0 = extractvalue { i64, i1 } %t0, 0
   %k0 = extractvalue { i64, i1 } %t0, 1
 
   %t1 = call { i64, i1 } @llvm.uadd.with.overflow.i64(i64 %x1, i64 %y1)
   %s1 = extractvalue { i64, i1 } %t1, 0