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spirv: air sub_with_overflow

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This commit is contained in:
Robin Voetter 2023-09-17 20:57:00 +02:00 committed by Andrew Kelley
parent 749307dbb2
commit 66b1f6c163
2 changed files with 26 additions and 10 deletions
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35
src/codegen/spirv.zig
View File

@ -1658,7 +1658,8 @@ pub const DeclGen = struct {
.rem_optimized,
=> try self.airArithOp(inst, .OpFRem, .OpSRem, .OpSRem, false),
.add_with_overflow => try self.airOverflowArithOp(inst),
.add_with_overflow => try self.airAddSubOverflow(inst, .OpIAdd, .OpULessThan, .OpSLessThan),
.sub_with_overflow => try self.airAddSubOverflow(inst, .OpISub, .OpUGreaterThan, .OpSGreaterThan),
.shuffle => try self.airShuffle(inst),
@ -1878,7 +1879,13 @@ pub const DeclGen = struct {
return result_id;
}
fn airOverflowArithOp(self: *DeclGen, inst: Air.Inst.Index) !?IdRef {
fn airAddSubOverflow(
self: *DeclGen,
inst: Air.Inst.Index,
comptime add: Opcode,
comptime ucmp: Opcode,
comptime scmp: Opcode,
) !?IdRef {
if (self.liveness.isUnused(inst)) return null;
const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
@ -1910,7 +1917,7 @@ pub const DeclGen = struct {
// TODO: Operations other than addition.
const value_id = self.spv.allocId();
try self.func.body.emit(self.spv.gpa, .OpIAdd, .{
try self.func.body.emit(self.spv.gpa, add, .{
.id_result_type = operand_ty_id,
.id_result = value_id,
.operand_1 = lhs,
@ -1920,8 +1927,9 @@ pub const DeclGen = struct {
const overflowed_id = switch (info.signedness) {
.unsigned => blk: {
// Overflow happened if the result is smaller than either of the operands. It doesn't matter which.
// For subtraction the conditions need to be swapped.
const overflowed_id = self.spv.allocId();
try self.func.body.emit(self.spv.gpa, .OpULessThan, .{
try self.func.body.emit(self.spv.gpa, ucmp, .{
.id_result_type = self.typeId(bool_ty_ref),
.id_result = overflowed_id,
.operand_1 = value_id,
@ -1930,13 +1938,22 @@ pub const DeclGen = struct {
break :blk overflowed_id;
},
.signed => blk: {
// Overflow happened if:
// lhs - rhs
// For addition, overflow happened if:
// - rhs is negative and value > lhs
// - rhs is positive and value < lhs
// This can be shortened to:
// (rhs < 0 && value > lhs) || (rhs >= 0 && value <= lhs)
// (rhs < 0 and value > lhs) or (rhs >= 0 and value <= lhs)
// = (rhs < 0) == (value > lhs)
// = (rhs < 0) == (lhs < value)
// Note that signed overflow is also wrapping in spir-v.
// For subtraction, overflow happened if:
// - rhs is negative and value < lhs
// - rhs is positive and value > lhs
// This can be shortened to:
// (rhs < 0 and value < lhs) or (rhs >= 0 and value >= lhs)
// = (rhs < 0) == (value < lhs)
// = (rhs < 0) == (lhs > value)
const rhs_lt_zero_id = self.spv.allocId();
const zero_id = try self.constInt(operand_ty_ref, 0);
@ -1948,11 +1965,11 @@ pub const DeclGen = struct {
});
const value_gt_lhs_id = self.spv.allocId();
try self.func.body.emit(self.spv.gpa, .OpSGreaterThan, .{
try self.func.body.emit(self.spv.gpa, scmp, .{
.id_result_type = self.typeId(bool_ty_ref),
.id_result = value_gt_lhs_id,
.operand_1 = value_id,
.operand_2 = lhs,
.operand_1 = lhs,
.operand_2 = value_id,
});
const overflowed_id = self.spv.allocId();

1
test/behavior/math.zig
View File

@ -1020,7 +1020,6 @@ test "@subWithOverflow" {
if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO
if (builtin.zig_backend == .stage2_spirv64) return error.SkipZigTest;
{
var a: u8 = 1;