[DAGCombine] Make sure we check the ResNo from UADDO before combining

[deadalnix]

Summary

UADDO has 2 result, and one must check the result no before doing any kind of combine. Without it, the transform is invalid.

[joerg]

This fixes the problem in mbedtls, thanks.

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

SDValue DAGCombiner::visitADDCARRY(SDNode *N) {
 
   return SDValue();
 }
 
 SDValue DAGCombiner::visitADDCARRYLike(SDValue N0, SDValue N1, SDValue CarryIn,
                                        SDNode *N) {
   // Iff the flag result is dead:
   // (addcarry (add|uaddo X, Y), 0, Carry) -> (addcarry X, Y, Carry)
-  if ((N0.getOpcode() == ISD::ADD || N0.getOpcode() == ISD::UADDO) &&
+  if ((N0.getOpcode() == ISD::ADD ||
+       (N0.getOpcode() == ISD::UADDO && N0.getResNo() == 0)) &&
       isNullConstant(N1) && !N->hasAnyUseOfValue(1))
     return DAG.getNode(ISD::ADDCARRY, SDLoc(N), N->getVTList(),
                        N0.getOperand(0), N0.getOperand(1), CarryIn);
 
   /**
    * When one of the addcarry argument is itself a carry, we may be facing
    * a diamond carry propagation. In which case we try to transform the DAG
    * to ensure linear carry propagation if that is possible.

test/CodeGen/X86/addcarry.ll

  %3 = add i128 %1, %0
  %4 = lshr i128 %3, 64
  %5 = add i128 %4, %2
  %6 = trunc i128 %5 to i8
  store i8 %6, i8* %r, align 4
  ret void
 }
 
+define i8 @e(i32* nocapture %a, i32 %b) nounwind {
+; CHECK-LABEL: e:
+; CHECK:       # BB#0:
+; CHECK-NEXT:    # kill: %ESI<def> %ESI<kill> %RSI<def>
+; CHECK-NEXT:    movl (%rdi), %ecx
+; CHECK-NEXT:    leal (%rsi,%rcx), %edx
+; CHECK-NEXT:    addl %esi, %edx
+; CHECK-NEXT:    setb %al
+; CHECK-NEXT:    addl %esi, %ecx
+; CHECK-NEXT:    movl %edx, (%rdi)
+; CHECK-NEXT:    adcb $0, %al
+; CHECK-NEXT:    retq
+  %1 = load i32, i32* %a, align 4
+  %2 = add i32 %1, %b
+  %3 = icmp ult i32 %2, %b
+  %4 = zext i1 %3 to i8
+  %5 = add i32 %2, %b
+  store i32 %5, i32* %a, align 4
+  %6 = icmp ult i32 %5, %b
+  %7 = zext i1 %6 to i8
+  %8 = add nuw nsw i8 %7, %4
+  ret i8 %8
+}
+
 %scalar = type { [4 x i64] }
 
 define %scalar @pr31719(%scalar* nocapture readonly %this, %scalar %arg.b) {
 ; CHECK-LABEL: pr31719:
 ; CHECK:       # BB#0: # %entry
 ; CHECK-NEXT:    addq (%rsi), %rdx
 ; CHECK-NEXT:    adcq 8(%rsi), %rcx
 ; CHECK-NEXT:    adcq 16(%rsi), %r8