[PATCH] D133471: [DAGCombiner][X86] Fold (sub (subcarry X, 0, Carry), Y) -> (subcarry X, Y, Carry)

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: RKSimon, spatel.
Herald added subscribers: StephenFan, ecnelises, pengfei, hiraditya.
Herald added a project: All.
craig.topper requested review of this revision.
Herald added a project: LLVM.

Fixes PR57576.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D133471

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/X86/pr57576.ll


Index: llvm/test/CodeGen/X86/pr57576.ll
===================================================================
--- llvm/test/CodeGen/X86/pr57576.ll
+++ llvm/test/CodeGen/X86/pr57576.ll
@@ -6,8 +6,7 @@
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    movq %rdi, %rax
 ; CHECK-NEXT:    subq %rdx, %rax
-; CHECK-NEXT:    sbbq $0, %rsi
-; CHECK-NEXT:    subq %rcx, %rsi
+; CHECK-NEXT:    sbbq %rcx, %rsi
 ; CHECK-NEXT:    movq %rsi, %rdx
 ; CHECK-NEXT:    retq
   %5 = zext i64 %1 to i128
Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3753,6 +3753,12 @@
       return DAG.getNode(ISD::ADD, DL, VT, N1, N0);
   }
 
+  // (sub (subcarry X, 0, Carry), Y) -> (subcarry X, Y, Carry)
+  if (N0.getOpcode() == ISD::SUBCARRY && isNullConstant(N0.getOperand(1)) &&
+      N0.getResNo() == 0)
+    return DAG.getNode(ISD::SUBCARRY, DL, N0->getVTList(),
+                       N0.getOperand(0), N1, N0.getOperand(2));
+
   if (TLI.isOperationLegalOrCustom(ISD::ADDCARRY, VT)) {
     // (sub Carry, X)  ->  (addcarry (sub 0, X), 0, Carry)
     if (SDValue Carry = getAsCarry(TLI, N0)) {


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