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[RISCV] Add a check in lowerSELECT after foldBinOpIntoSelectIfProfitable #97391

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Merged
merged 1 commit into from
Jul 5, 2024
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[RISCV] Add a check in lowerSELECT after foldBinOpIntoSelectIfProfitable #97391

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6 changes: 5 additions & 1 deletion llvm/lib/Target/RISCV/RISCVISelLowering.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7664,7 +7664,11 @@ SDValue RISCVTargetLowering::lowerSELECT(SDValue Op, SelectionDAG &DAG) const {
if (SDValue NewSel = foldBinOpIntoSelectIfProfitable(*Op->use_begin(),
DAG, Subtarget)) {
DAG.ReplaceAllUsesWith(BinOp, &NewSel);
return lowerSELECT(NewSel, DAG);
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Can you please add a comment explaining why the check is needed - it doesn't seem obvious.

// Opcode check is necessary because foldBinOpIntoSelectIfProfitable
// may return a constant node and cause crash in lowerSELECT.
if (NewSel.getOpcode() == ISD::SELECT)
return lowerSELECT(NewSel, DAG);
return NewSel;
}
}
}
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14 changes: 14 additions & 0 deletions llvm/test/CodeGen/RISCV/fold-binop-into-select-return-constant.ll
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@@ -0,0 +1,14 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
; RUN: llc -mtriple=riscv64 -mattr=+m < %s | FileCheck %s

define i64 @fold_binop_into_select_return_constant(i1 %c) {
; CHECK-LABEL: fold_binop_into_select_return_constant:
; CHECK: # %bb.0: # %entry
; CHECK-NEXT: li a0, 0
; CHECK-NEXT: ret
entry:
%select1 = select i1 %c, i32 4, i32 8
%select2 = sext i32 %select1 to i64
%div1 = sdiv i64 %select2, -5141143369814759789
ret i64 %div1
}
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