[X86] Combine ADC(ADD(X,Y),0,Carry) -> ADC(X,Y,Carry)

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D120435

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -52150,6 +52150,13 @@ static SDValue combineADC(SDNode *N, SelectionDAG &DAG,
     return DAG.getNode(X86ISD::ADC, SDLoc(N), VTs, LHS, RHS, Flags);
   }
 
+  // Fold ADC(ADD(X,Y),0,Carry) -> ADC(X,Y,Carry)
+  // iff the flag result is dead.
+  if (LHS.getOpcode() == ISD::ADD && isNullConstant(RHS) &&
+      !N->hasAnyUseOfValue(1))
+    return DAG.getNode(X86ISD::ADC, SDLoc(N), N->getVTList(), LHS.getOperand(0),
+                       LHS.getOperand(1), CarryIn);
+
   return SDValue();
 }
 

llvm/test/CodeGen/X86/addcarry.ll

@@ -1366,11 +1366,9 @@ define void @add_U256_without_i128_or_recursive(%uint256* sret(%uint256) %0, %ui
 define i32 @addcarry_ult(i32 %a, i32 %b, i32 %x, i32 %y) {
 ; CHECK-LABEL: addcarry_ult:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    # kill: def $esi killed $esi def $rsi
-; CHECK-NEXT:    # kill: def $edi killed $edi def $rdi
-; CHECK-NEXT:    leal (%rdi,%rsi), %eax
+; CHECK-NEXT:    movl %edi, %eax
 ; CHECK-NEXT:    cmpl %ecx, %edx
-; CHECK-NEXT:    adcl $0, %eax
+; CHECK-NEXT:    adcl %esi, %eax
 ; CHECK-NEXT:    retq
   %s = add i32 %a, %b
   %k = icmp ult i32 %x, %y
@@ -1382,11 +1380,9 @@ define i32 @addcarry_ult(i32 %a, i32 %b, i32 %x, i32 %y) {
 define i32 @addcarry_ugt(i32 %a, i32 %b, i32 %x, i32 %y) {
 ; CHECK-LABEL: addcarry_ugt:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    # kill: def $esi killed $esi def $rsi
-; CHECK-NEXT:    # kill: def $edi killed $edi def $rdi
-; CHECK-NEXT:    leal (%rdi,%rsi), %eax
+; CHECK-NEXT:    movl %edi, %eax
 ; CHECK-NEXT:    cmpl %edx, %ecx
-; CHECK-NEXT:    adcl $0, %eax
+; CHECK-NEXT:    adcl %esi, %eax
 ; CHECK-NEXT:    retq
   %s = add i32 %a, %b
   %k = icmp ugt i32 %x, %y