[PATCH] D118362: [DAGCombine] Extend and refactor combineCarryDiamond()

[Paweł Bylica via Phabricator via llvm-commits]

chfast created this revision.
chfast added reviewers: craig.topper, RKSimon, lebedev.ri, davezarzycki, spatel.
Herald added subscribers: ecnelises, pengfei, hiraditya.
chfast requested review of this revision.
Herald added a project: LLVM.

This is mostly refactoring to use existing helpers:

- isOperandOf()
- getAsCarry()

The second one finds more candidates for being a carry flag.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D118362

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/X86/addcarry.ll


Index: llvm/test/CodeGen/X86/addcarry.ll
===================================================================
--- llvm/test/CodeGen/X86/addcarry.ll
+++ llvm/test/CodeGen/X86/addcarry.ll
@@ -451,12 +451,9 @@
 ; 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)
Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3059,21 +3059,26 @@
 // 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 as Carry0 and the add/sub of the
-  // carry/borrow in as Carry1. (The top and middle uaddo nodes respectively in
-  // the above ASCII art.)
-  if (Carry1.getOperand(0) != Carry0.getValue(0) &&
-      Carry1.getOperand(1) != Carry0.getValue(0))
+  // 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();


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