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shader: compute scalar signed-overflow SCC with compares instead of XOR masks

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nmzik
2026-10-21 23:22:54 +02:00
parent 330d373dc6
commit ae47ac26e7
1 changed files with 6 additions and 4 deletions
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src/graphics/shader/recompiler/frontend/translate/Control.cpp
+6 -4
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@@ -143,11 +143,13 @@ void Translator::S_ADD_SUB_I32(const Decoder::Instruction& inst, bool subtract)
const auto lhs = ReadU32(inst.src0); const auto lhs = ReadU32(inst.src0);
const auto rhs = ReadU32(inst.src1); const auto rhs = ReadU32(inst.src1);
const auto result = subtract ? ir.ISub(lhs, rhs) : ir.IAdd(lhs, rhs); 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). // Signed overflow moves the result past lhs the wrong way for the sign of rhs.
const auto other = subtract ? ir.BitwiseXor(lhs, rhs) : ir.BitwiseXor(rhs, result); const auto ge = [&](IR::Value a, IR::Value b) {
const auto overflow = ir.BitwiseAnd(ir.BitwiseXor(lhs, result), other); return IR::U1(ir.Emit(IR::ValueOpcode::SGreaterThanEqual32, {a, b}));
};
const auto moved = subtract ? ge(lhs, result) : ge(result, lhs);
WriteOperand(DestinationOperand(inst), result); WriteOperand(DestinationOperand(inst), result);
ir.SetScc(ir.UGreaterThan(overflow, IR::U32(IR::Value(0x7fffffffu)))); ir.SetScc(IR::U1(ir.Emit(IR::ValueOpcode::LogicalXor, {moved, ge(rhs, IR::Value(0u))})));
} }
void Translator::S_LSHL_ADD_U32(const Decoder::Instruction& inst, uint32_t shift_amount) { void Translator::S_LSHL_ADD_U32(const Decoder::Instruction& inst, uint32_t shift_amount) {