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Implement saturating_{add, sub} for non-native integer types #156

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Merged
merged 5 commits into from
Apr 6, 2022
Merged

Implement saturating_{add, sub} for non-native integer types #156

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56983cf
test: Remove redundant code from `tests/run/int.rs`
yvt Apr 1, 2022
837a446
test: Test more integer types and checked arithmetic in `tests/run/in…
yvt Apr 5, 2022
00677e5
Implement `saturating_{add, sub}` for non-native integer types
yvt Apr 1, 2022
5061e3a
Remove redundant assertions
yvt Apr 6, 2022
a7a09d5
Wrap numbers with `black_box` in-line, remove `one`
yvt Apr 6, 2022
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92 changes: 57 additions & 35 deletions src/intrinsic/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -967,34 +967,55 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
}

fn saturating_add(&mut self, lhs: RValue<'gcc>, rhs: RValue<'gcc>, signed: bool, width: u64) -> RValue<'gcc> {
let func = self.current_func.borrow().expect("func");

let result_type = lhs.get_type();
if signed {
// Algorithm from: https://stackoverflow.com/a/56531252/389119
let after_block = func.new_block("after");
let func_name =
match width {
8 => "__builtin_add_overflow",
16 => "__builtin_add_overflow",
32 => "__builtin_sadd_overflow",
64 => "__builtin_saddll_overflow",
128 => "__builtin_add_overflow",
_ => unreachable!(),
};
let overflow_func = self.context.get_builtin_function(func_name);
let result_type = lhs.get_type();
// Based on algorithm from: https://stackoverflow.com/a/56531252/389119
let func = self.current_func.borrow().expect("func");
let res = func.new_local(None, result_type, "saturating_sum");
let overflow = self.overflow_call(overflow_func, &[lhs, rhs, res.get_address(None)], None);
let supports_native_type = self.is_native_int_type(result_type);
let overflow =
if supports_native_type {
let func_name =
match width {
8 => "__builtin_add_overflow",
16 => "__builtin_add_overflow",
32 => "__builtin_sadd_overflow",
64 => "__builtin_saddll_overflow",
128 => "__builtin_add_overflow",
_ => unreachable!(),
};
let overflow_func = self.context.get_builtin_function(func_name);
self.overflow_call(overflow_func, &[lhs, rhs, res.get_address(None)], None)
}
else {
let func_name =
match width {
128 => "__rust_i128_addo",
_ => unreachable!(),
};
let param_a = self.context.new_parameter(None, result_type, "a");
let param_b = self.context.new_parameter(None, result_type, "b");
let result_field = self.context.new_field(None, result_type, "result");
let overflow_field = self.context.new_field(None, self.bool_type, "overflow");
let return_type = self.context.new_struct_type(None, "result_overflow", &[result_field, overflow_field]);
let func = self.context.new_function(None, FunctionType::Extern, return_type.as_type(), &[param_a, param_b], func_name, false);
let result = self.context.new_call(None, func, &[lhs, rhs]);
let overflow = result.access_field(None, overflow_field);
let int_result = result.access_field(None, result_field);
self.llbb().add_assignment(None, res, int_result);
overflow
};

let then_block = func.new_block("then");
let after_block = func.new_block("after");

let unsigned_type = self.context.new_int_type(width as i32 / 8, false);
let shifted = self.context.new_cast(None, lhs, unsigned_type) >> self.context.new_rvalue_from_int(unsigned_type, width as i32 - 1);
let uint_max = self.context.new_unary_op(None, UnaryOp::BitwiseNegate, unsigned_type,
self.context.new_rvalue_from_int(unsigned_type, 0)
);
let int_max = uint_max >> self.context.new_rvalue_one(unsigned_type);
then_block.add_assignment(None, res, self.context.new_cast(None, shifted + int_max, result_type));
// Return `result_type`'s maximum or minimum value on overflow
// NOTE: convert the type to unsigned to have an unsigned shift.
let unsigned_type = result_type.to_unsigned(&self.cx);
let shifted = self.gcc_lshr(self.gcc_int_cast(lhs, unsigned_type), self.gcc_int(unsigned_type, width as i64 - 1));
let uint_max = self.gcc_not(self.gcc_int(unsigned_type, 0));
let int_max = self.gcc_lshr(uint_max, self.gcc_int(unsigned_type, 1));
then_block.add_assignment(None, res, self.gcc_int_cast(self.gcc_add(shifted, int_max), result_type));
then_block.end_with_jump(None, after_block);

self.llbb().end_with_conditional(None, overflow, then_block, after_block);
Expand All @@ -1006,20 +1027,20 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
res.to_rvalue()
}
else {
assert!(!signed);
// Algorithm from: http://locklessinc.com/articles/sat_arithmetic/
let res = lhs + rhs;
let res_type = res.get_type();
let cond = self.context.new_comparison(None, ComparisonOp::LessThan, res, lhs);
let value = self.context.new_unary_op(None, UnaryOp::Minus, res_type, self.context.new_cast(None, cond, res_type));
res | value
let res = self.gcc_add(lhs, rhs);
let cond = self.gcc_icmp(IntPredicate::IntULT, res, lhs);
let value = self.gcc_neg(self.gcc_int_cast(cond, result_type));
self.gcc_or(res, value)
}
}

// Algorithm from: https://locklessinc.com/articles/sat_arithmetic/
fn saturating_sub(&mut self, lhs: RValue<'gcc>, rhs: RValue<'gcc>, signed: bool, width: u64) -> RValue<'gcc> {
let result_type = lhs.get_type();
if signed {
// Also based on algorithm from: https://stackoverflow.com/a/56531252/389119
let result_type = lhs.get_type();
// Based on algorithm from: https://stackoverflow.com/a/56531252/389119
let func = self.current_func.borrow().expect("func");
let res = func.new_local(None, result_type, "saturating_diff");
let supports_native_type = self.is_native_int_type(result_type);
Expand Down Expand Up @@ -1059,6 +1080,7 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
let then_block = func.new_block("then");
let after_block = func.new_block("after");

// Return `result_type`'s maximum or minimum value on overflow
// NOTE: convert the type to unsigned to have an unsigned shift.
let unsigned_type = result_type.to_unsigned(&self.cx);
let shifted = self.gcc_lshr(self.gcc_int_cast(lhs, unsigned_type), self.gcc_int(unsigned_type, width as i64 - 1));
Expand All @@ -1076,11 +1098,11 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
res.to_rvalue()
}
else {
let res = lhs - rhs;
let comparison = self.context.new_comparison(None, ComparisonOp::LessThanEquals, res, lhs);
let comparison = self.context.new_cast(None, comparison, lhs.get_type());
let unary_op = self.context.new_unary_op(None, UnaryOp::Minus, comparison.get_type(), comparison);
self.and(res, unary_op)
assert!(!signed);
let res = self.gcc_sub(lhs, rhs);
let comparison = self.gcc_icmp(IntPredicate::IntULE, res, lhs);
let value = self.gcc_neg(self.gcc_int_cast(comparison, result_type));
self.gcc_and(res, value)
}
}
}
Expand Down
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