[SelectionDAG] Propagate Disjoint flag.

[fengfeng09]

No description provided.

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Author: fengfeng (fengfeng09)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/88370.diff

2 Files Affected:

• (modified) llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (+2)
• (modified) llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp (+2)

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 8fe074666a3dc9..59ef66fba73164 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -9530,6 +9530,8 @@ static SDValue combineShiftOfShiftedLogic(SDNode *Shift, SelectionDAG &DAG) {
   SDValue ShiftSumC = DAG.getConstant(*C0Val + C1Val, DL, ShiftAmtVT);
   SDValue NewShift1 = DAG.getNode(ShiftOpcode, DL, VT, X, ShiftSumC);
   SDValue NewShift2 = DAG.getNode(ShiftOpcode, DL, VT, Y, C1);
+  // Propogate flags.
+  SelectionDAG::FlagInserter FlagsInserter(DAG, LogicOp->getFlags());
   return DAG.getNode(LogicOpcode, DL, VT, NewShift1, NewShift2);
 }
 
diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 409d66adfd67d1..dd5c3d741aa7dc 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -544,6 +544,8 @@ bool TargetLowering::ShrinkDemandedConstant(SDValue Op,
     if (!C.isSubsetOf(DemandedBits)) {
       EVT VT = Op.getValueType();
       SDValue NewC = TLO.DAG.getConstant(DemandedBits & C, DL, VT);
+      // Propogate flags.
+      SelectionDAG::FlagInserter FlagsInserter(TLO.DAG, Op->getFlags());
       SDValue NewOp = TLO.DAG.getNode(Opcode, DL, VT, Op.getOperand(0), NewC);
       return TLO.CombineTo(Op, NewOp);
     }

[RKSimon]

Tests?

[dtcxzyw]

Please add some tests for these changes.

[goldsteinn]

Tests?

Just a note, the general practice is to "pre commit" your tests. What that means is your PR should have two commits.
Commit 1) Tests w/o your implementation
Commit 2) Your implementation w/ updated tests (using llvm/utils/update_llc_test_checks.py in this case).

That way we can see the diff.

[fengfeng09]

Thanks all, updated.

[arsenm]

https://alive2.llvm.org/ce/z/ttZfv8

[jayfoad]

Typo in subject "propagate"

[dtcxzyw]

LGTM. Nice catch!

[topperc]

Why do we need to use FlagInserter? Can't we pass the flags to the last argument of getNode?

[fengfeng09]

I have no write access to the repo，could someone help me merge this PR？

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