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shader: eliminate predicates for empty branch detours

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This commit is contained in:
nmzik
2026-10-18 20:37:39 +02:00
parent e9bcc77e0b
commit 8b51370ca1
2 changed files with 107 additions and 24 deletions
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src/graphics/shader/recompiler/ir/passes/DeadCodeElimination.cpp
+54 -24
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@@ -30,32 +30,62 @@ void RemoveIdentities(Program& program) {
}
void EliminateDeadCode(const BlockList& blocks) {
std::vector<Inst*> pending;
for (auto* block: blocks) {
for (auto& inst: *block) {
// Retained resource-planning instructions live outside the block list.
inst.live = inst.MayHaveSideEffects() || std::ranges::any_of(inst.Uses(),
[](const Use& use) { return use.user->Parent() == nullptr; });
if (inst.live) pending.push_back(&inst);
}
}
while (!pending.empty()) {
const auto* inst = pending.back();
pending.pop_back();
for (size_t arg = 0; arg < inst->NumArgs(); ++arg) {
auto* input = inst->Arg(arg).TryInstruction();
if (input != nullptr && input->Parent() != nullptr && !input->live) {
input->live = true;
pending.push_back(input);
bool changed;
do {
std::vector<Inst*> pending;
for (auto* block: blocks) {
for (auto& inst: *block) {
// Retained resource-planning instructions live outside the block list.
inst.live = inst.MayHaveSideEffects() || std::ranges::any_of(inst.Uses(),
[](const Use& use) { return use.user->Parent() == nullptr; });
if (inst.live) pending.push_back(&inst);
}
}
}
// Unlink every dead operand before freeing nodes in a dead Phi cycle.
for (auto* block: blocks)
for (auto& inst: *block)
if (!inst.live) inst.Invalidate();
for (auto* block: blocks)
std::erase_if(block->Instructions(), [](const Inst& inst) { return !inst.live; });
while (!pending.empty()) {
const auto* inst = pending.back();
pending.pop_back();
for (size_t arg = 0; arg < inst->NumArgs(); ++arg) {
auto* input = inst->Arg(arg).TryInstruction();
if (input != nullptr && input->Parent() != nullptr && !input->live) {
input->live = true;
pending.push_back(input);
}
}
}
// Unlink every dead operand before freeing nodes in a dead Phi cycle.
for (auto* block: blocks)
for (auto& inst: *block)
if (!inst.live) inst.Invalidate();
for (auto* block: blocks)
std::erase_if(block->Instructions(), [](const Inst& inst) { return !inst.live; });
changed = false;
for (auto* block: blocks) {
const auto& term = block->terminator;
if (term.kind != CFG::TerminatorKind::ConditionalBranch || term.loop_header ||
block->condition.IsImmediate()) continue;
for (const bool take_true: {false, true}) {
const auto* empty = take_true ? term.false_block : term.true_block;
const auto* merge = take_true ? term.true_block : term.false_block;
if (empty == nullptr || merge == nullptr || !empty->empty() ||
empty->terminator.loop_header || merge->terminator.loop_header ||
empty->terminator.kind != CFG::TerminatorKind::Branch ||
empty->terminator.true_block != merge ||
std::ranges::any_of(*merge, [](const Inst& inst) {
return inst.GetOpcode() == ValueOpcode::Phi;
})) continue;
// Keep the CFG and SSA edges intact; only the empty detour's predicate is dead.
for (auto& inst: *block) {
if (inst.GetOpcode() == ValueOpcode::Reference &&
inst.Arg(0).Resolve() == block->condition.Resolve())
inst.SetArg(0, Value(take_true));
}
block->condition = Value(take_true);
changed = true;
break;
}
}
} while (changed);
}
} // namespace Libs::Graphics::ShaderRecompiler::IR