[llvm] Have fallback for getSwappedCondition(CC) in the Fold check. (PR #160753)

[via llvm-commits]

https://github.com/AZero13 created https://github.com/llvm/llvm-project/pull/160753

NFC for now, but if we simplify nodes where we can remove a compare with 0 and we are stuck with condition codes MI or PL, we are in trouble, as you cannot swap that.

>From 41af802963239941ca446c8009f498fc3331a833 Mon Sep 17 00:00:00 2001
From: AZero13 <gfunni234 at gmail.com>
Date: Thu, 25 Sep 2025 14:37:04 -0400
Subject: [PATCH] Have fallback for getSwappedCondition(CC)

NFC for now, but if we simplify nodes where we can remove a compare with 0 and we are stuck with condition codes MI or PL, we are in trouble, as you cannot swap that.
---
 llvm/lib/Target/AArch64/AArch64ISelLowering.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index a4c1e265f0e63..0e68d5b570c28 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -25764,8 +25764,11 @@ static SDValue reassociateCSELOperandsForCSE(SDNode *N, SelectionDAG &DAG) {
     // Try again with the operands of the SUBS instruction and the condition
     // swapped. Due to canonicalization, this only helps for non-constant
     // operands of the SUBS instruction.
+    auto NewCC = getSwappedCondition(CC);
+    if (NewCC == AArch64CC::AL)
+      return SDValue();
     std::swap(CmpOpToMatch, CmpOpOther);
-    if (SDValue R = Fold(getSwappedCondition(CC), CmpOpToMatch, CmpOpToMatch))
+    if (SDValue R = Fold(NewCC, CmpOpToMatch, CmpOpToMatch))
       return R;
     return SDValue();
   }