[CIR] Emit nsw flag for unary integer operations #1485
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andykaylor
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Mar 17, 2025
| @@ -467,7 +467,8 @@ class ScalarExprEmitter : public StmtVisitor<ScalarExprEmitter, mlir::Value> { | |||
| auto Kind = | |||
| E->isIncrementOp() ? cir::UnaryOpKind::Inc : cir::UnaryOpKind::Dec; | |||
| // NOTE(CIR): clang calls CreateAdd but folds this to a unary op | |||
| value = emitUnaryOp(E, Kind, input); | |||
| value = | |||
| emitUnaryOp(E, Kind, input, /*nsw=*/type->isSignedIntegerType()); | |||
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Classic codegen doesn't add nsw here. Based on the checks above, we should only get here if E->canOverflow() is false. For instance, I think we hit this code with this:
short f(short s) {
s++;
return s;
}
In this case, s is promoted to int before the operation, so it can't overflow, and classic codegen doesn't set the nsw flag.
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Overall approach looks good, I don't have anything to add besides @andykaylor comments
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Resolves #1477 .