[llvm] [SelectionDAG] Prevent combination on inconsistent type in `combineCarryDiamond` (PR #84888)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-selectiondag

Author: XChy (XChy)

<details>
<summary>Changes</summary>

Fixes #<!-- -->84831
When matching carry pattern with `getAsCarry`, it may produce different type of carryout. This patch checks such case and does early exit.

I'm new to DAG, any suggestion is appreciated.

---
Full diff: https://github.com/llvm/llvm-project/pull/84888.diff


2 Files Affected:

- (modified) llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (+3) 
- (modified) llvm/test/CodeGen/X86/addcarry.ll (+23) 


``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index cdcb7114640471..7e8b1d82b22504 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3442,6 +3442,9 @@ static SDValue combineCarryDiamond(SelectionDAG &DAG, const TargetLowering &TLI,
     return SDValue();
   if (Opcode != ISD::UADDO && Opcode != ISD::USUBO)
     return SDValue();
+  // Guarantee identical type of CarryOut
+  if (N->getValueType(0) != Carry0.getValue(1).getValueType())
+    return SDValue();
 
   // 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).
diff --git a/llvm/test/CodeGen/X86/addcarry.ll b/llvm/test/CodeGen/X86/addcarry.ll
index 3fc4ed99fad0fa..f0efd6fe5de370 100644
--- a/llvm/test/CodeGen/X86/addcarry.ll
+++ b/llvm/test/CodeGen/X86/addcarry.ll
@@ -1490,3 +1490,26 @@ define { i64, i64 } @addcarry_commutative_2(i64 %x0, i64 %x1, i64 %y0, i64 %y1)
   %r1 = insertvalue { i64, i64 } %r0, i64 %b1s, 1
   ret { i64, i64 } %r1
 }
+
+define i1 @pr84831(i64 %0) {
+; CHECK-LABEL: pr84831:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    testq %rdi, %rdi
+; CHECK-NEXT:    setne %al
+; CHECK-NEXT:    xorl %ecx, %ecx
+; CHECK-NEXT:    addb $-1, %al
+; CHECK-NEXT:    adcq $1, %rcx
+; CHECK-NEXT:    setb %al
+; CHECK-NEXT:    retq
+  %2 = icmp ult i64 0, %0
+  %3 = add i64 0, 1
+  %4 = icmp ult i64 %3, 0
+  %5 = zext i1 %2 to i64
+  %6 = add i64 %3, %5
+  %7 = icmp ult i64 %6, %3
+  %8 = zext i1 %4 to i63
+  %9 = zext i1 %7 to i63
+  %new0 = or i63 %8, %9
+  %last = trunc i63 %new0 to i1
+  ret i1 %last
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/84888