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shader: compute scalar signed-overflow and shift-add carry SCC with fewer ops

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This commit is contained in:
nmzik
2026-10-21 22:56:21 +02:00
parent aacf15fd0b
commit 2862ad5b25
1 changed files with 13 additions and 19 deletions
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src/graphics/shader/recompiler/frontend/translate/Control.cpp
+13 -19
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@@ -140,29 +140,23 @@ void Translator::S_ABSDIFF_I32(const Decoder::Instruction& inst) {
}
void Translator::S_ADD_SUB_I32(const Decoder::Instruction& inst, bool subtract) {
const auto lhs = ReadU32(inst.src0);
const auto rhs = ReadU32(inst.src1);
const auto result = subtract ? ir.ISub(lhs, rhs) : ir.IAdd(lhs, rhs);
const auto shift = IR::U32(IR::Value(31u));
const auto lhs_sign = ir.ShiftRightLogical(lhs, shift);
const auto rhs_sign = ir.ShiftRightLogical(rhs, shift);
const auto out_sign = ir.ShiftRightLogical(result, shift);
const auto inputs = subtract ? ir.INotEqual(lhs_sign, rhs_sign) : ir.IEqual(lhs_sign, rhs_sign);
const auto changed = ir.INotEqual(lhs_sign, out_sign);
const auto lhs = ReadU32(inst.src0);
const auto rhs = ReadU32(inst.src1);
const auto result = subtract ? ir.ISub(lhs, rhs) : ir.IAdd(lhs, rhs);
// Overflow sets the sign bit of lhs ^ result and of rhs ^ result (add) or lhs ^ rhs (sub).
const auto other = subtract ? ir.BitwiseXor(lhs, rhs) : ir.BitwiseXor(rhs, result);
const auto overflow = ir.BitwiseAnd(ir.BitwiseXor(lhs, result), other);
WriteOperand(DestinationOperand(inst), result);
ir.SetScc(ir.LogicalAnd(inputs, changed));
ir.SetScc(ir.UGreaterThan(overflow, IR::U32(IR::Value(0x7fffffffu))));
}
void Translator::S_LSHL_ADD_U32(const Decoder::Instruction& inst, uint32_t shift_amount) {
const auto lhs = ReadU32(inst.src0);
const auto shift = IR::U32(IR::Value(shift_amount));
const auto rhs = ReadU32(inst.src1);
const auto shifted = ir.ShiftLeftLogical(lhs, shift);
const auto result = ir.IAdd(shifted, rhs);
const auto add_carry = ir.ULessThan(result, shifted);
const auto inverse_shift = ir.ISub(IR::U32(IR::Value(32u)), shift);
const auto shifted_out = ir.ShiftRightLogical(lhs, inverse_shift);
const auto shift_carry = ir.INotEqual(shifted_out, IR::U32(IR::Value(0u)));
const auto lhs = ReadU32(inst.src0);
const auto rhs = ReadU32(inst.src1);
const auto shifted = ir.ShiftLeftLogical(lhs, IR::U32(IR::Value(shift_amount)));
const auto result = ir.IAdd(shifted, rhs);
const auto add_carry = ir.ULessThan(result, shifted);
const auto shift_carry = ir.UGreaterThan(lhs, IR::U32(IR::Value(~0u >> shift_amount)));
WriteOperand(DestinationOperand(inst), result);
ir.SetScc(ir.LogicalOr(add_carry, shift_carry));
}