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add compile error for compile-time integer cast truncating bits

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closes #371
This commit is contained in:
Andrew Kelley 2017-05-16 17:04:35 -04:00
parent f375063917
commit 9851a943ed
3 changed files with 30 additions and 6 deletions
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20
src/ir.cpp
View File

@ -7053,12 +7053,20 @@ static IrInstruction *ir_analyze_widen_or_shorten(IrAnalyze *ira, IrInstruction
ConstExprValue *val = ir_resolve_const(ira, target, UndefBad); ConstExprValue *val = ir_resolve_const(ira, target, UndefBad);
if (!val) if (!val)
return ira->codegen->invalid_instruction; return ira->codegen->invalid_instruction;
if (val->data.x_bignum.is_negative && wanted_type->id == TypeTableEntryIdInt && if (wanted_type->id == TypeTableEntryIdInt) {
!wanted_type->data.integral.is_signed) if (val->data.x_bignum.is_negative && !wanted_type->data.integral.is_signed) {
{ ir_add_error(ira, source_instr,
ir_add_error(ira, source_instr, buf_sprintf("attempt to cast negative value to unsigned integer"));
buf_sprintf("attempt to cast negative value to unsigned integer")); return ira->codegen->invalid_instruction;
return ira->codegen->invalid_instruction; }
if (!bignum_fits_in_bits(&val->data.x_bignum, wanted_type->data.integral.bit_count,
wanted_type->data.integral.is_signed))
{
ir_add_error(ira, source_instr,
buf_sprintf("cast from '%s' to '%s' truncates bits",
buf_ptr(&target->value.type->name), buf_ptr(&wanted_type->name)));
return ira->codegen->invalid_instruction;
}
} }
IrInstruction *result = ir_create_const(&ira->new_irb, source_instr->scope, IrInstruction *result = ir_create_const(&ira->new_irb, source_instr->scope,
source_instr->source_node, wanted_type); source_instr->source_node, wanted_type);

8
test/cases/eval.zig
View File

@ -314,3 +314,11 @@ const global_array = {
} }
result result
}; };
test "compile-time downcast when the bits fit" {
comptime {
const spartan_count: u16 = 255;
const byte = u8(spartan_count);
assert(byte == 255);
}
}

8
test/compile_errors.zig
View File

@ -1827,4 +1827,12 @@ pub fn addCases(cases: &tests.CompileErrorContext) {
\\} \\}
, ,
".tmp_source.zig:4:17: error: division by zero is undefined"); ".tmp_source.zig:4:17: error: division by zero is undefined");
cases.add("compile-time integer cast truncates bits",
\\comptime {
\\ const spartan_count: u16 = 300;
\\ const byte = u8(spartan_count);
\\}
,
".tmp_source.zig:3:20: error: cast from 'u16' to 'u8' truncates bits");
} }