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Sema: combine signed->unsigned and shrinkage runtime checks in intCast

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William Sengir 2022-03-28 13:08:50 -07:00
parent cf20b97b71
commit fa42fcbc1a
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1 changed files with 35 additions and 17 deletions
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52
src/Sema.zig
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@ -6971,6 +6971,7 @@ fn intCast(
operand_src: LazySrcLoc,
runtime_safety: bool,
) CompileError!Air.Inst.Ref {
// TODO: Add support for vectors
const dest_is_comptime_int = try sema.checkIntType(block, dest_ty_src, dest_ty);
_ = try sema.checkIntType(block, operand_src, sema.typeOf(operand));
@ -7006,25 +7007,42 @@ fn intCast(
const wanted_info = dest_ty.intInfo(target);
const actual_bits = actual_info.bits;
const wanted_bits = wanted_info.bits;
const actual_value_bits = actual_bits - @boolToInt(actual_info.signedness == .signed);
const wanted_value_bits = wanted_bits - @boolToInt(wanted_info.signedness == .signed);
// requirement: signed to unsigned >= 0
if (actual_info.signedness == .signed and
wanted_info.signedness == .unsigned)
{
const zero_inst = try sema.addConstant(sema.typeOf(operand), Value.zero);
const is_in_range = try block.addBinOp(.cmp_gte, operand, zero_inst);
try sema.addSafetyCheck(block, is_in_range, .cast_truncated_data);
// range shrinkage
// requirement: int value fits into target type
if (wanted_value_bits < actual_value_bits) {
const dest_max_val = try dest_ty.maxInt(sema.arena, target);
const dest_max = try sema.addConstant(operand_ty, dest_max_val);
const diff = try block.addBinOp(.subwrap, dest_max, operand);
if (actual_info.signedness == .signed) {
// Reinterpret the sign-bit as part of the value. This will make
// negative differences (`operand` > `dest_max`) appear too big.
const unsigned_operand_ty = try Type.Tag.int_unsigned.create(sema.arena, actual_bits);
const diff_unsigned = try block.addBitCast(unsigned_operand_ty, diff);
// If the destination type is signed, then we need to double its
// range to account for negative values.
const dest_range_val = if (wanted_info.signedness == .signed) range_val: {
const range_minus_one = try dest_max_val.shl(Value.one, unsigned_operand_ty, sema.arena, target);
break :range_val try range_minus_one.intAdd(Value.one, unsigned_operand_ty, sema.arena, target);
} else dest_max_val;
const dest_range = try sema.addConstant(unsigned_operand_ty, dest_range_val);
const is_in_range = try block.addBinOp(.cmp_lte, diff_unsigned, dest_range);
try sema.addSafetyCheck(block, is_in_range, .cast_truncated_data);
} else {
const is_in_range = try block.addBinOp(.cmp_lte, diff, dest_max);
try sema.addSafetyCheck(block, is_in_range, .cast_truncated_data);
}
}
// requirement: unsigned int value fits into target type
if (actual_bits > wanted_bits or
(actual_bits == wanted_bits and
actual_info.signedness == .unsigned and
wanted_info.signedness == .signed))
{
const max_int = try dest_ty.maxInt(sema.arena, target);
const max_int_inst = try sema.addConstant(operand_ty, max_int);
const is_in_range = try block.addBinOp(.cmp_lte, operand, max_int_inst);
// no shrinkage, yes sign loss
// requirement: signed to unsigned >= 0
else if (actual_info.signedness == .signed and wanted_info.signedness == .unsigned) {
const zero_inst = try sema.addConstant(operand_ty, Value.zero);
const is_in_range = try block.addBinOp(.cmp_gte, operand, zero_inst);
try sema.addSafetyCheck(block, is_in_range, .cast_truncated_data);
}
}