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Bitwidth zero for discriminants #792

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Merged
merged 5 commits into from
Oct 31, 2025
Merged

Bitwidth zero for discriminants #792

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3ae1286
Use bitwidth=0 for discriminant values, allow comparisons
jberthold Oct 30, 2025
c23e367
fix up switchMatch equations to deal with discriminant ints
jberthold Oct 30, 2025
0b8e7ba
disambiguate special rules for comparison to avoid branches, test exp…
jberthold Oct 31, 2025
68623a1
Merge branch 'master' into bitwidth-zero-for-discriminants
jberthold Oct 31, 2025
5f4344f
revert bad stable-mir-json change
jberthold Oct 31, 2025
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3 changes: 2 additions & 1 deletion kmir/src/kmir/kdist/mir-semantics/kmir.md
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Original file line number Diff line number Diff line change
Expand Up @@ -173,7 +173,8 @@ will be `129`.

rule #switchMatch(0, BoolVal(B) ) => notBool B
rule #switchMatch(1, BoolVal(B) ) => B
rule #switchMatch(I, Integer(I2, WIDTH, _)) => I ==Int truncate(I2, WIDTH, Unsigned)
rule #switchMatch(I, Integer(I2, WIDTH, _)) => I ==Int truncate(I2, WIDTH, Unsigned) requires 0 <Int WIDTH
rule #switchMatch(I, Integer(I2, 0 , _)) => I ==Int I2
```

`Return` simply returns from a function call, using the information
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41 changes: 16 additions & 25 deletions kmir/src/kmir/kdist/mir-semantics/rt/data.md
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Expand Up @@ -1015,10 +1015,9 @@ The `getTyOf` helper applies the projections from the `Place` to determine the `
syntax Evaluation ::= #discriminant ( Evaluation , MaybeTy ) [strict(1)]
// ----------------------------------------------------------------
rule <k> #discriminant(Aggregate(IDX, _), TY:Ty)
=> Integer(#lookupDiscriminant(lookupTy(TY), IDX), #discriminantSize(lookupTy(TY)), false)
=> Integer(#lookupDiscriminant(lookupTy(TY), IDX), 0, false) // HACK: bit width 0 means "flexible"
...
</k>
requires #discriminantSize(lookupTy(TY)) =/=Int 0

syntax Int ::= #lookupDiscriminant ( TypeInfo , VariantIdx ) [function, total]
| #lookupDiscrAux ( Discriminants , Int ) [function]
Expand All @@ -1029,27 +1028,6 @@ The `getTyOf` helper applies the projections from the `Place` to determine the `
// --------------------------------------------------------------------
rule #lookupDiscrAux( discriminant(RESULT) _ , IDX) => RESULT requires IDX ==Int 0
rule #lookupDiscrAux( _:Discriminant MORE:Discriminants, IDX) => #lookupDiscrAux(MORE, IDX -Int 1) requires 0 <Int IDX [owise]

syntax Int ::= #discriminantSize ( TypeInfo ) [function, total]
| #discriminantSize ( LayoutShape ) [function, total]
| #discriminantSize ( Scalar ) [function, total]
| #intLength (IntegerLength) [function, total]
// ------------------------------------------------------------
rule #discriminantSize(typeInfoEnumType(_, _, _, _, someLayoutShape(LAYOUT))) => #discriminantSize(LAYOUT)
rule #discriminantSize(_OTHER_TYPE:TypeInfo) => 0 [owise]

rule #discriminantSize(layoutShape(_, variantsShapeMultiple(mk(TAG, _, _, _)), _, _, _)) => #discriminantSize(TAG)
rule #discriminantSize(_OTHER:LayoutShape) => 0 [owise]

rule #discriminantSize(scalarInitialized(mk(primitiveInt(mk(INTLENGTH, _SIGNED)), _VALIDRANGE))) => #intLength(INTLENGTH)
rule #discriminantSize(scalarInitialized(mk(primitivePointer(_) , _VALIDRANGE))) => 64 // pointer size assumed 64 bit
rule #discriminantSize(_OTHER:Scalar) => 0 [owise]

rule #intLength(integerLengthI8) => 8
rule #intLength(integerLengthI16) => 16
rule #intLength(integerLengthI32) => 32
rule #intLength(integerLengthI64) => 64
rule #intLength(integerLengthI128) => 128
```

```k
Expand Down Expand Up @@ -1422,7 +1400,7 @@ If none of the `enum` variants has any fields, the `Transmute` of a number to th
rule <k> #discriminant(
thunk(#cast (Integer(DATA, _, false), castKindTransmute, _, TY)),
TY
) => Integer(DATA, #discriminantSize(lookupTy(TY)), false)
) => Integer(DATA, 0, false) // HACK: bit width 0 means "flexible"
...
</k>
requires #isEnumWithoutFields(lookupTy(TY))
Expand Down Expand Up @@ -1705,14 +1683,27 @@ The argument types must be the same for all comparison operations, however this
rule #applyBinOp(OP, Integer(VAL1, WIDTH, SIGN), Integer(VAL2, WIDTH, SIGN), _)
=>
BoolVal(cmpOpInt(OP, VAL1, VAL2))
requires isComparison(OP)
andBool WIDTH =/=Int 0
[preserves-definedness] // OP known to be a comparison

// HACK: accept bit width 0 in comparisons (coming from discriminants)
rule #applyBinOp(OP, Integer(VAL1, 0, false), Integer(VAL2, _WIDTH, _SIGN), _)
=>
BoolVal(cmpOpInt(OP, VAL1, VAL2))
requires isComparison(OP)
[priority(55), preserves-definedness] // OP known to be a comparison
rule #applyBinOp(OP, Integer(VAL1, _WIDTH, _SIGN_), Integer(VAL2, 0, false), _)
=>
BoolVal(cmpOpInt(OP, VAL1, VAL2))
requires isComparison(OP)
[preserves-definedness] // OP known to be a comparison

rule #applyBinOp(OP, BoolVal(VAL1), BoolVal(VAL2), _)
=>
BoolVal(cmpOpBool(OP, VAL1, VAL2))
requires isComparison(OP)
[preserves-definedness] // OP known to be a comparison
[priority(60), preserves-definedness] // OP known to be a comparison
```

The `binOpCmp` operation returns `-1`, `0`, or `+1` (the behaviour of Rust's `std::cmp::Ordering as i8`), indicating `LE`, `EQ`, or `GT`.
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2 changes: 1 addition & 1 deletion kmir/src/tests/integration/data/exec-smir/enum/enum.state
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Expand Up @@ -47,7 +47,7 @@
ListItem ( newLocal ( ty ( 16 ) , mutabilityNot ) )
ListItem ( newLocal ( ty ( 28 ) , mutabilityNot ) )
ListItem ( typedValue ( Moved , ty ( 6 ) , mutabilityMut ) )
ListItem ( typedValue ( Integer ( 9090 , 16 , false ) , ty ( 29 ) , mutabilityMut ) )
ListItem ( typedValue ( Integer ( 9090 , 0 , false ) , ty ( 29 ) , mutabilityMut ) )
ListItem ( newLocal ( ty ( 26 ) , mutabilityNot ) )
ListItem ( newLocal ( ty ( 28 ) , mutabilityMut ) )
</locals>
Expand Down