[llvm-branch-commits] [llvm] 8646466 - [DAGCombiner] Restrict combineOrOfSetCCToUSUBOCarry to ZeroOrOneBooleanContent. (#224759)

[Tobias Hieta via llvm-branch-commits]

Author: Craig Topper
Date: 2026-09-23T13:54:13+02:00
New Revision: 8646466e3a4fcde4fc72ca9ece6945f74790697c

URL: https://github.com/llvm/llvm-project/commit/8646466e3a4fcde4fc72ca9ece6945f74790697c
DIFF: https://github.com/llvm/llvm-project/commit/8646466e3a4fcde4fc72ca9ece6945f74790697c.diff

LOG: [DAGCombiner] Restrict combineOrOfSetCCToUSUBOCarry to ZeroOrOneBooleanContent. (#224759)

We need to ensure the carry in matches boolean contents. We are checking
MaskedValueIsZero which is only valid for ZeroOrOneBooleanContent.

We could check ComputeNumSignBits for ZeroOrNegativeOneBooleanContent,
but no in tree target supports USUBO_CARRY and
ZeroOrNegativeOneBooleanContent.

This was an oversight in #223396 due to incorrect documentation for
USUBO_CARRY. I will fix that in a separate patch.

(cherry picked from commit 51d290508d4dd980c3ba03bcc873926c41c6e591)

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 8f07e311f11ea..478685084d4de 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3968,9 +3968,12 @@ static SDValue combineOrOfSetCCToUSUBOCarry(SDNode *N, SelectionDAG &DAG,
                                                     *DAG.getContext(), IntVT)))
     return SDValue();
 
-  // USUBO_CARRY's carry-in must be 0 or 1, which the matched pattern does not
-  // guarantee.
-  if (!DAG.MaskedValueIsZero(
+  // USUBO_CARRY's carry-in must match boolean contents, which the matched
+  // pattern does not guarantee.
+  // TODO: Extend to other boolean contents.
+  if (TLI.getBooleanContents(IntVT) !=
+          TargetLowering::ZeroOrOneBooleanContent ||
+      !DAG.MaskedValueIsZero(
           CarryIn,
           APInt::getBitsSetFrom(CarryIn.getScalarValueSizeInBits(), 1)))
     return SDValue();