[llvm] aa83bdd - [DAGCombiner][X86] Fold (sub (subcarry X, 0, Carry), Y) -> (subcarry X, Y, Carry)

[Craig Topper via llvm-commits]

Author: Craig Topper
Date: 2022-09-08T22:56:46-07:00
New Revision: aa83bdd1982fbf1174d0769a7842a86779041f37

URL: https://github.com/llvm/llvm-project/commit/aa83bdd1982fbf1174d0769a7842a86779041f37
DIFF: https://github.com/llvm/llvm-project/commit/aa83bdd1982fbf1174d0769a7842a86779041f37.diff

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

Fixes PR57576.

Differential Revision: https://reviews.llvm.org/D133471

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index d2640b6eda0fc..c215772449e19 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3753,6 +3753,12 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
       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 && N0.hasOneUse())
+    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)) {

diff  --git a/llvm/test/CodeGen/X86/pr57576.ll b/llvm/test/CodeGen/X86/pr57576.ll
index ecc30f60532c7..b44eaf3c041be 100644
--- a/llvm/test/CodeGen/X86/pr57576.ll
+++ b/llvm/test/CodeGen/X86/pr57576.ll
@@ -6,8 +6,7 @@ define { i64, i64 } @sub(i64 noundef %0, i64 noundef %1, i64 noundef %2, i64 nou
 ; 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