| ... | ... | @@ -3661,6 +3661,7 @@ const NavGen = struct { |
| 3661 | 3661 | comptime ucmp: CmpPredicate, |
| 3662 | 3662 | comptime scmp: CmpPredicate, |
| 3663 | 3663 | ) !?IdRef { |
| 3664 | _ = scmp; |
| 3664 | 3665 | // Note: OpIAddCarry and OpISubBorrow are not really useful here: For unsigned numbers, |
| 3665 | 3666 | // there is in both cases only one extra operation required. For signed operations, |
| 3666 | 3667 | // the overflow bit is set then going from 0x80.. to 0x00.., but this doesn't actually |
| ... | ... | @@ -3689,26 +3690,30 @@ const NavGen = struct { |
| 3689 | 3690 | // Overflow happened if the result is smaller than either of the operands. It doesn't matter which. |
| 3690 | 3691 | // For subtraction the conditions need to be swapped. |
| 3691 | 3692 | .unsigned => try self.buildCmp(ucmp, result, lhs), |
| 3692 | | // For addition, overflow happened if: |
| 3693 | | // - rhs is negative and value > lhs |
| 3694 | | // - rhs is positive and value < lhs |
| 3695 | | // This can be shortened to: |
| 3696 | | // (rhs < 0 and value > lhs) or (rhs >= 0 and value <= lhs) |
| 3697 | | // = (rhs < 0) == (value > lhs) |
| 3698 | | // = (rhs < 0) == (lhs < value) |
| 3699 | | // Note that signed overflow is also wrapping in spir-v. |
| 3700 | | // For subtraction, overflow happened if: |
| 3701 | | // - rhs is negative and value < lhs |
| 3702 | | // - rhs is positive and value > lhs |
| 3703 | | // This can be shortened to: |
| 3704 | | // (rhs < 0 and value < lhs) or (rhs >= 0 and value >= lhs) |
| 3705 | | // = (rhs < 0) == (value < lhs) |
| 3706 | | // = (rhs < 0) == (lhs > value) |
| 3693 | // For signed operations, we check the signs of the operands and the result. |
| 3707 | 3694 | .signed => blk: { |
| 3695 | // Signed overflow detection using the sign bits of the operands and the result. |
| 3696 | // For addition (a + b), overflow occurs if the operands have the same sign |
| 3697 | // and the result's sign is different from the operands' sign. |
| 3698 | // (sign(a) == sign(b)) && (sign(a) != sign(result)) |
| 3699 | // For subtraction (a - b), overflow occurs if the operands have different signs |
| 3700 | // and the result's sign is different from the minuend's (a's) sign. |
| 3701 | // (sign(a) != sign(b)) && (sign(a) != sign(result)) |
| 3708 | 3702 | const zero = Temporary.init(rhs.ty, try self.constInt(rhs.ty, 0)); |
| 3709 | | const rhs_lt_zero = try self.buildCmp(.s_lt, rhs, zero); |
| 3710 | | const result_gt_lhs = try self.buildCmp(scmp, lhs, result); |
| 3711 | | break :blk try self.buildCmp(.l_eq, rhs_lt_zero, result_gt_lhs); |
| 3703 | |
| 3704 | const lhs_is_neg = try self.buildCmp(.s_lt, lhs, zero); |
| 3705 | const rhs_is_neg = try self.buildCmp(.s_lt, rhs, zero); |
| 3706 | const result_is_neg = try self.buildCmp(.s_lt, result, zero); |
| 3707 | |
| 3708 | const signs_match = try self.buildCmp(.l_eq, lhs_is_neg, rhs_is_neg); |
| 3709 | const result_sign_differs = try self.buildCmp(.l_ne, lhs_is_neg, result_is_neg); |
| 3710 | |
| 3711 | const overflow_condition = if (add == .i_add) |
| 3712 | signs_match |
| 3713 | else // .i_sub |
| 3714 | try self.buildUnary(.l_not, signs_match); |
| 3715 | |
| 3716 | break :blk try self.buildBinary(.l_and, overflow_condition, result_sign_differs); |
| 3712 | 3717 | }, |
| 3713 | 3718 | }; |
| 3714 | 3719 | |
Ivan Stepanov <ivanstepanovftw@gmail.com> 2025-07-01 14:25:04+02:00
Alex Rønne Petersen <alex@alexrp.com> 2025-07-01 19:26:21+02:00
src