shader: share one find-first-bit lowering for S_FF0/FF1/FLBIT_I32_B64 and remove FindUMsb64

src/graphics/shader/recompiler/backend/spirv/spirvEmitterAlu.cpp

@@ -5,18 +5,6 @@
 namespace Libs::Graphics::ShaderRecompiler::Spirv::Emitter {
 namespace {
 
-struct Pair {
-	uint32_t low  = 0;
-	uint32_t high = 0;
-};
-
-Pair ExtractPair(EmitterState& state, uint32_t value) {
-	Pair result {state.builder.AllocateId(), state.builder.AllocateId()};
-	state.builder.AddFunction(spv::OpCompositeExtract, TypeU32(state), result.low, value, 0);
-	state.builder.AddFunction(spv::OpCompositeExtract, TypeU32(state), result.high, value, 1);
-	return result;
-}
-
 uint32_t EmitMinMaxF64(EmitterState& state, uint32_t lhs, uint32_t rhs, bool max_value) {
 	const auto bits_type = TypeU32Vector(state, 2);
 	const auto lhs_bits = Unary(state, spv::OpBitcast, bits_type, lhs);
@@ -160,18 +148,6 @@ uint32_t EmitFPMad32(EmitterState& state, uint32_t a, uint32_t b, uint32_t c) {
 	return sum;
 }
 
-uint32_t EmitFindUMsb64(EmitterState& state, uint32_t value) {
-	// GLSL FindUMsb is restricted to 32-bit components.
-	const auto unpacked = Unary(state, spv::OpBitcast, TypeU32Vector(state, 2), value);
-	const auto pair =
-	    ExtractPair(state, EmitExt(state, TypeU32Vector(state, 2), GLSLstd450FindUMsb, {unpacked}));
-	const auto high_found =
-	    Binary(state, spv::OpINotEqual, TypeBool(state), pair.high, ConstantU32(state, UINT32_MAX));
-	return Select(state, TypeU32(state), high_found,
-	              Binary(state, spv::OpIAdd, TypeU32(state), pair.high, ConstantU32(state, 32)),
-	              pair.low);
-}
-
 uint32_t EmitConvertU16U32(EmitterState& state, uint32_t arg0) {
 	return EmitNative<spv::OpBitwiseAnd, IR::Type::U16>(state, arg0, ConstantU32(state, 0xffffu));
 }

src/graphics/shader/recompiler/backend/spirv/spirvEmitterInstructions.h

@@ -92,7 +92,6 @@ EMIT_NATIVE(BitReverse32, OpBitReverse, U32, uint32_t)
 EMIT_NATIVE(BitCount32, OpBitCount, U32, uint32_t)
 inline constexpr auto EmitFindILsb32 = EmitGlsl<GLSLstd450FindILsb, IR::Type::U32, uint32_t>;
 inline constexpr auto EmitFindUMsb32 = EmitGlsl<GLSLstd450FindUMsb, IR::Type::U32, uint32_t>;
-uint32_t EmitFindUMsb64(EmitterState& state, uint32_t arg0);
 inline constexpr auto EmitSMin32 = EmitGlsl<GLSLstd450SMin, IR::Type::U32, uint32_t, uint32_t>;
 inline constexpr auto EmitSMax32 = EmitGlsl<GLSLstd450SMax, IR::Type::U32, uint32_t, uint32_t>;
 inline constexpr auto EmitUMin32 = EmitGlsl<GLSLstd450UMin, IR::Type::U32, uint32_t, uint32_t>;

src/graphics/shader/recompiler/frontend/translate/Integer.cpp

@@ -221,19 +221,21 @@ void Translator::V_XOR3_B32(const Decoder::Instruction& inst) {
 	WriteOperand(DestinationOperand(inst), result);
 }
 
-void Translator::S_FF_I32_B64(const Decoder::Instruction& inst, bool find_zero) {
+void Translator::S_FF_I32_B64(const Decoder::Instruction& inst, bool find_zero, bool from_msb) {
 	auto source = ReadU32Pair(inst.src0);
-	if (find_zero) {
+	for (auto& word: source) {
-		source[0] = ir.BitwiseNot(source[0]);
+		word = find_zero ? ir.BitwiseNot(word) : word;
-		source[1] = ir.BitwiseNot(source[1]);
 	}
-	const auto low_lsb       = IR::U32(ir.Emit(IR::ValueOpcode::FindILsb32, {source[0]}));
+	if (from_msb) {
-	const auto high_lsb      = IR::U32(ir.Emit(IR::ValueOpcode::FindILsb32, {source[1]}));
+		// The leading bit index is the trailing bit index of the bit-reversed 64-bit value.
-	const auto high_position = ir.IAdd(high_lsb, IR::U32(IR::Value(32u)));
+		source = {IR::U32(ir.Emit(IR::ValueOpcode::BitReverse32, {source[1]})),
-	const auto result        = ir.Select(ir.INotEqual(source[0], IR::U32(IR::Value(0u))), low_lsb,
+		          IR::U32(ir.Emit(IR::ValueOpcode::BitReverse32, {source[0]}))};
-	                                     ir.Select(ir.INotEqual(source[1], IR::U32(IR::Value(0u))),
+	}
-	                                               high_position, IR::U32(IR::Value(0xffffffffu))));
+	// FindILsb returns ~0 for zero, so OR-ing 32 keeps a missing high bit at ~0 (-1).
-	WriteOperand(DestinationOperand(inst), result);
+	const auto low  = ir.Emit(IR::ValueOpcode::FindILsb32, {source[0]});
+	const auto high = ir.BitwiseOr(IR::U32(ir.Emit(IR::ValueOpcode::FindILsb32, {source[1]})),
+	                               IR::U32(IR::Value(32u)));
+	WriteOperand(DestinationOperand(inst), ir.Emit(IR::ValueOpcode::UMin32, {low, high}));
 }
 
 void Translator::V_FFBH_32(const Decoder::Instruction& inst, bool sign) {
@@ -248,17 +250,6 @@ void Translator::V_FFBH_32(const Decoder::Instruction& inst, bool sign) {
 	WriteOperand(DestinationOperand(inst), result);
 }
 
-void Translator::S_FLBIT_I32_B64(const Decoder::Instruction& inst) {
-	const auto source   = ReadU64(inst.src0);
-	const auto msb      = IR::U32(ir.Emit(IR::ValueOpcode::FindUMsb64, {source}));
-	const auto position = ir.ISub(IR::U32(IR::Value(63u)), msb);
-	const auto nonzero =
-	    IR::U1(ir.Emit(IR::ValueOpcode::INotEqual64,
-	                   {source, ir.ConstructU64(IR::U32(IR::Value(0u)), IR::U32(IR::Value(0u)))}));
-	const auto result = ir.Select(nonzero, position, IR::U32(IR::Value(0xffffffffu)));
-	WriteOperand(DestinationOperand(inst), result);
-}
-
 void Translator::Integer24(const Decoder::Instruction& inst, bool sign, bool addend) {
 	const auto extract24 = [&](IR::U32 value) {
 		return IR::U32(

src/graphics/shader/recompiler/frontend/translate/Scalar.cpp

@@ -238,10 +238,10 @@ void Translator::EmitScalar(const Decoder::Instruction& inst) {
 			return ComposedIntegerBinary(inst, IR::ValueOpcode::BitwiseOr32, false, true, true);
 		case O::S_XNOR_B32:
 			return ComposedIntegerBinary(inst, IR::ValueOpcode::BitwiseXor32, false, true, true);
-		case O::S_FF0_I32_B64: return S_FF_I32_B64(inst, true);
+		case O::S_FF0_I32_B64: return S_FF_I32_B64(inst, true, false);
-		case O::S_FF1_I32_B64: return S_FF_I32_B64(inst, false);
+		case O::S_FF1_I32_B64: return S_FF_I32_B64(inst, false, false);
 		case O::S_FLBIT_I32_B32: return V_FFBH_32(inst, false);
-		case O::S_FLBIT_I32_B64: return S_FLBIT_I32_B64(inst);
+		case O::S_FLBIT_I32_B64: return S_FF_I32_B64(inst, false, true);
 
 		case O::S_BITSET0_B32: return S_BITSET_B32(inst, false);
 		case O::S_BITSET1_B32: return S_BITSET_B32(inst, true);

src/graphics/shader/recompiler/frontend/translate/Translator.h

@@ -187,9 +187,8 @@ private:
 	void V_AND_OR_B32(const Decoder::Instruction& inst);
 	void V_OR3_B32(const Decoder::Instruction& inst);
 	void V_XOR3_B32(const Decoder::Instruction& inst);
-	void S_FF_I32_B64(const Decoder::Instruction& inst, bool find_zero);
+	void S_FF_I32_B64(const Decoder::Instruction& inst, bool find_zero, bool from_msb);
 	void V_FFBH_32(const Decoder::Instruction& inst, bool sign);
-	void S_FLBIT_I32_B64(const Decoder::Instruction& inst);
 	void Integer24(const Decoder::Instruction& inst, bool sign, bool addend);
 	void V_MAD_U64_U32(const Decoder::Instruction& inst);
 	void V_SAD_U32(const Decoder::Instruction& inst);

src/graphics/shader/recompiler/ir/opcodes/ValueOpcodes.inc

@@ -118,7 +118,6 @@ VALUE_OPCODE(BitwiseNot32, U32, U32)
 VALUE_OPCODE(BitReverse32, U32, U32)
 VALUE_OPCODE(BitCount32, U32, U32)
 VALUE_OPCODE(FindUMsb32, U32, U32)
-VALUE_OPCODE(FindUMsb64, U32, U64)
 VALUE_OPCODE(FindILsb32, U32, U32)
 VALUE_OPCODE(SMin32, U32, U32, U32)
 VALUE_OPCODE(UMin32, U32, U32, U32)

src/graphics/shader/recompiler/ir/passes/ConstantPropagation.cpp

@@ -651,10 +651,15 @@ void FoldInstruction(Block& block, Block::iterator instruction,
 			}
 			return;
 		}
-		case ValueOpcode::BitCount32: {
+		case ValueOpcode::BitCount32:
+		case ValueOpcode::FindILsb32: {
 			const auto value = Arg(inst, 0);
 			if (IsImmediate(value, Type::U32)) {
-				Replace(inst, Value(static_cast<uint32_t>(std::popcount(value.U32()))));
+				const auto bits = value.U32();
+				Replace(inst, Value(static_cast<uint32_t>(
+				    inst.GetOpcode() == ValueOpcode::BitCount32 ? std::popcount(bits)
+				    : bits == 0u                                ? -1
+				                                                : std::countr_zero(bits))));
 			}
 			return;
 		}
@@ -667,7 +672,9 @@ void FoldInstruction(Block& block, Block::iterator instruction,
 			});
 			return;
 		case ValueOpcode::UMin32:
-			FoldU32(inst, [](uint32_t a, uint32_t b) { return std::min(a, b); });
+			if (!FoldU32(inst, [](uint32_t a, uint32_t b) { return std::min(a, b); })) {
+				ReplaceBinaryIdentity(inst, Type::U32, ~0u);
+			}
 			return;
 		case ValueOpcode::UMax32:
 			FoldU32(inst, [](uint32_t a, uint32_t b) { return std::max(a, b); });