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shader: lower complete wave minima for sparse fragment subgroups

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This commit is contained in:
nmzik
2026-10-14 18:03:48 +02:00
parent 892e70c8a1
commit 302240da70
12 changed files with 330 additions and 8 deletions
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src/graphics/shader/recompiler/ir/ShaderIR.h
+1
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@@ -507,6 +507,7 @@ struct ShaderInfo {
bool subgroup_ballot = false;
bool subgroup_barrier = false;
bool subgroup_shuffle = false;
bool subgroup_arithmetic = false;
bool subgroup_local_invocation_id = false;
bool compute_derivatives = false;
bool image_gather_extended = false;
src/graphics/shader/recompiler/ir/opcodes/ValueOpcodes.inc
+1
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@@ -226,6 +226,7 @@ VALUE_OPCODE(LaneId, U32)
VALUE_OPCODE(Ballot, U32x4, U1)
VALUE_OPCODE(ReadFirstLane, U32, U32, U1)
VALUE_OPCODE(ReadLane, U32, U32, U32)
VALUE_OPCODE(SubgroupUMinU32, U32, U32)
VALUE_OPCODE(WriteLane, U32, U32, U32, U32)
VALUE_OPCODE(Permlane16U32, U32, U32, U32, U32, U1)
VALUE_OPCODE(PermuteU32, U32, U32, U32, U1)
src/graphics/shader/recompiler/ir/passes/ReadLaneElimination.cpp
+119
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@@ -99,6 +99,114 @@ Value GetRealValue(PhiMap& phi_map, Value source, uint32_t lane, uint32_t wave_s
return Value(&phi);
}
// A full-EXEC prefix scan with both half-wave endpoint reads is a reduction.
// Fragment subgroups may have no physical invocation at either endpoint.
class UMinReductionMatcher {
public:
explicit UMinReductionMatcher(Block* block): block(block) {}
Value Match(const Inst& minimum) {
const auto* low = Get(minimum.Arg(0), ValueOpcode::ReadLane);
const auto* high = Get(minimum.Arg(1), ValueOpcode::ReadLane);
if (low == nullptr || high == nullptr || low->Arg(0).Resolve() != high->Arg(0).Resolve()) {
return {};
}
const auto lane = [](Value value, uint32_t expected) {
value = value.Resolve();
return value.IsImmediate() && value.GetType() == Type::U32 &&
value.U32() % 64u == expected;
};
if (!((lane(low->Arg(1), 31) && lane(high->Arg(1), 63)) ||
(lane(low->Arg(1), 63) && lane(high->Arg(1), 31)))) {
return {};
}
const auto* joined = Get(Unwrap(low->Arg(0)), ValueOpcode::UMin32);
if (joined == nullptr) return {};
for (size_t index = 0; index < 2; index++) {
auto attempt = *this;
const auto* cross = attempt.Get(attempt.Unwrap(joined->Arg(index)), ValueOpcode::Permlane16U32);
if (cross == nullptr) continue;
const auto flags = cross->Flags<PermlaneFlags>();
auto prefix = attempt.Unwrap(joined->Arg(1 - index));
if (!flags.x16 || flags.fetch_inactive || !flags.bound_control ||
cross->Arg(1).Resolve() != Value(UINT32_MAX) ||
cross->Arg(2).Resolve() != Value(UINT32_MAX) ||
!attempt.FullExec(cross->Arg(3)) || attempt.Unwrap(cross->Arg(0)) != prefix) {
continue;
}
for (const uint32_t shift: {8u, 4u, 2u, 1u}) {
prefix = attempt.MatchRow(prefix, shift);
}
prefix = attempt.Unwrap(prefix);
if (prefix.IsEmpty() || attempt.saved_exec.IsEmpty()) return prefix;
const auto* seed = attempt.Get(prefix, ValueOpcode::SelectU32);
if (seed != nullptr && seed->Arg(2).Resolve() == Value(UINT32_MAX)) {
const auto predicate = seed->Arg(0).Resolve();
const auto* subset = attempt.Get(predicate, ValueOpcode::LogicalAnd);
if (predicate == attempt.saved_exec ||
(subset != nullptr && (subset->Arg(0).Resolve() == attempt.saved_exec ||
subset->Arg(1).Resolve() == attempt.saved_exec))) {
return prefix;
}
}
}
return {};
}
private:
Inst* Get(Value value, ValueOpcode opcode) const {
auto* inst = value.Resolve().TryInstruction();
return inst != nullptr && inst->Parent() == block && inst->GetOpcode() == opcode
? inst : nullptr;
}
bool FullExec(Value predicate) {
predicate = predicate.Resolve();
if (predicate == Value(true)) return true;
const auto* either = Get(predicate, ValueOpcode::LogicalOr);
if (either == nullptr) return false;
for (size_t index = 0; index < 2; index++) {
const auto* negate = Get(either->Arg(index), ValueOpcode::LogicalNot);
if (negate == nullptr || negate->Arg(0).Resolve() != either->Arg(1 - index).Resolve()) continue;
const auto original = negate->Arg(0).Resolve();
if (saved_exec.IsEmpty()) saved_exec = original;
return saved_exec == original;
}
return false;
}
Value Unwrap(Value value) {
while (const auto* select = Get(value, ValueOpcode::SelectU32)) {
if (!FullExec(select->Arg(0))) break;
value = select->Arg(1);
}
return value.Resolve();
}
static bool IsRowShift(const Inst& inst, uint32_t shift) {
const auto flags = inst.Flags<DppMoveFlags>();
return flags.control == 0x110u + shift && flags.row_mask == 0xf &&
flags.bank_mask == 0xf && !flags.fetch_inactive && !flags.bound_control && !flags.dpp8;
}
Value MatchRow(Value value, uint32_t shift) {
const auto* update = Get(Unwrap(value), ValueOpcode::DppUpdateU32);
if (update == nullptr || !IsRowShift(*update, shift) || !FullExec(update->Arg(2))) return {};
const auto* minimum = Get(update->Arg(0), ValueOpcode::UMin32);
if (minimum == nullptr) return {};
for (size_t index = 0; index < 2; index++) {
const auto* move = Get(minimum->Arg(index), ValueOpcode::DppMoveU32);
if (move == nullptr || !IsRowShift(*move, shift) || !FullExec(move->Arg(1))) continue;
const auto previous = Unwrap(minimum->Arg(1 - index));
if (Unwrap(move->Arg(0)) == previous && Unwrap(update->Arg(1)) == previous) return previous;
}
return {};
}
Block* block;
Value saved_exec;
};
} // namespace
ReadLaneStats EliminateReadLane(Program& program, uint32_t wave_size) {
@@ -109,6 +217,17 @@ ReadLaneStats EliminateReadLane(Program& program, uint32_t wave_size) {
for (auto* block: program.blocks) {
for (auto& inst: *block) {
if (wave_size == 64u && inst.GetOpcode() == ValueOpcode::UMin32) {
const auto seed = UMinReductionMatcher(block).Match(inst);
if (!seed.IsEmpty()) {
const auto position = std::find_if(block->begin(), block->end(),
[&](const Inst& candidate) { return &candidate == &inst; });
auto& reduction = *block->PrependNewInst(position, ValueOpcode::SubgroupUMinU32, {seed});
inst.ReplaceUsesWith(Value(&reduction));
stats.rewritten_reductions++;
}
continue;
}
if (inst.GetOpcode() != ValueOpcode::ReadLane) {
continue;
}
src/graphics/shader/recompiler/ir/passes/ReadLaneElimination.h
+2 -1
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@@ -5,7 +5,8 @@
namespace Libs::Graphics::ShaderRecompiler::IR {
struct ReadLaneStats {
uint32_t rewritten_reads = 0;
uint32_t rewritten_reads = 0;
uint32_t rewritten_reductions = 0;
};
[[nodiscard]] ReadLaneStats EliminateReadLane(Program& program, uint32_t wave_size);
src/graphics/shader/recompiler/ir/passes/ShaderInfoCollection.cpp
+2 -1
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@@ -514,6 +514,7 @@ void Visit(Program& program, ShaderStageInputInfo input_info, InputUsage& inputs
inst.Flags<CFG::BranchCondition>() != CFG::BranchCondition::ScalarInstruction;
break;
case ValueOpcode::Ballot: info.subgroup_ballot = true; break;
case ValueOpcode::SubgroupUMinU32: info.subgroup_arithmetic = true; break;
case ValueOpcode::DppMoveU32:
case ValueOpcode::ReadFirstLane:
case ValueOpcode::ReadLane: {
@@ -574,7 +575,7 @@ void CollectShaderInfo(Program& program, ShaderStageInputInfo input_info) {
info.live_buffers = 0;
info.has_bitwise_xor = info.uses_lds = info.uses_gds = info.uses_flattened_srt =
info.uses_dispatch_threads = info.uses_swizzle = false;
info.bvh = info.subgroup_ballot = info.subgroup_barrier = info.subgroup_shuffle =
info.bvh = info.subgroup_ballot = info.subgroup_barrier = info.subgroup_shuffle = info.subgroup_arithmetic =
info.subgroup_local_invocation_id = info.compute_derivatives = info.image_gather_extended =
info.function_lds = info.function_scratch = info.pixel_valid_mask = info.buffer_int64_atomics =
info.buffer_u8 = info.buffer_u16 = info.shared_int64_atomics = info.coherent_buffers = info.float64 = false;