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// Copyright 2022 The Tint Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "src/tint/transform/demote_to_helper.h"
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include "src/tint/program_builder.h"
#include "src/tint/sem/block_statement.h"
#include "src/tint/sem/call.h"
#include "src/tint/sem/function.h"
#include "src/tint/sem/statement.h"
#include "src/tint/transform/utils/hoist_to_decl_before.h"
#include "src/tint/type/reference.h"
#include "src/tint/utils/map.h"
TINT_INSTANTIATE_TYPEINFO(tint::transform::DemoteToHelper);
using namespace tint::number_suffixes; // NOLINT
namespace tint::transform {
DemoteToHelper::DemoteToHelper() = default;
DemoteToHelper::~DemoteToHelper() = default;
Transform::ApplyResult DemoteToHelper::Apply(const Program* src, const DataMap&, DataMap&) const {
auto& sem = src->Sem();
// Collect the set of functions that need to be processed.
// A function needs to be processed if it is reachable by a shader that contains a discard at
// any point in its call hierarchy.
std::unordered_set<const sem::Function*> functions_to_process;
for (auto* func : src->AST().Functions()) {
if (!func->IsEntryPoint()) {
continue;
}
// Determine whether this entry point and its callees need to be transformed.
bool needs_transform = false;
if (sem.Get(func)->DiscardStatement()) {
needs_transform = true;
} else {
for (auto* callee : sem.Get(func)->TransitivelyCalledFunctions()) {
if (callee->DiscardStatement()) {
needs_transform = true;
break;
}
}
}
if (!needs_transform) {
continue;
}
// Process the entry point and its callees.
functions_to_process.insert(sem.Get(func));
for (auto* callee : sem.Get(func)->TransitivelyCalledFunctions()) {
functions_to_process.insert(callee);
}
}
if (functions_to_process.empty()) {
return SkipTransform;
}
ProgramBuilder b;
CloneContext ctx{&b, src, /* auto_clone_symbols */ true};
// Create a module-scope flag that indicates whether the current invocation has been discarded.
auto flag = b.Symbols().New("tint_discarded");
b.GlobalVar(flag, ast::AddressSpace::kPrivate, b.Expr(false));
// Replace all discard statements with a statement that marks the invocation as discarded.
ctx.ReplaceAll([&](const ast::DiscardStatement*) -> const ast::Statement* {
return b.Assign(flag, b.Expr(true));
});
// Insert a conditional discard at the end of each entry point that does not end with a return.
for (auto* func : functions_to_process) {
if (func->Declaration()->IsEntryPoint()) {
auto* sem_body = sem.Get(func->Declaration()->body);
if (sem_body->Behaviors().Contains(sem::Behavior::kNext)) {
ctx.InsertBack(func->Declaration()->body->statements,
b.If(flag, b.Block(b.Discard())));
}
}
}
HoistToDeclBefore hoist_to_decl_before(ctx);
// Mask all writes to host-visible memory using the discarded flag.
// We also insert a discard statement before all return statements in entry points for shaders
// that discard.
std::unordered_map<const type::Type*, Symbol> atomic_cmpxchg_result_types;
for (auto* node : src->ASTNodes().Objects()) {
Switch(
node,
// Mask assignments to storage buffer variables.
[&](const ast::AssignmentStatement* assign) {
// Skip writes in functions that are not called from shaders that discard.
auto* func = sem.Get(assign)->Function();
if (functions_to_process.count(func) == 0) {
return;
}
// Skip phony assignments.
if (assign->lhs->Is<ast::PhonyExpression>()) {
return;
}
// Skip writes to invocation-private address spaces.
auto* ref = sem.Get(assign->lhs)->Type()->As<type::Reference>();
switch (ref->AddressSpace()) {
case ast::AddressSpace::kStorage:
// Need to mask these.
break;
case ast::AddressSpace::kFunction:
case ast::AddressSpace::kPrivate:
case ast::AddressSpace::kOut:
// Skip these.
return;
default:
TINT_UNREACHABLE(Transform, b.Diagnostics())
<< "write to unhandled address space: " << ref->AddressSpace();
}
// Mask the assignment using the invocation-discarded flag.
ctx.Replace(assign, b.If(b.Not(flag), b.Block(ctx.Clone(assign))));
},
// Mask builtins that write to host-visible memory.
[&](const ast::CallExpression* call) {
auto* sem_call = sem.Get<sem::Call>(call);
auto* stmt = sem_call ? sem_call->Stmt() : nullptr;
auto* func = stmt ? stmt->Function() : nullptr;
auto* builtin = sem_call ? sem_call->Target()->As<sem::Builtin>() : nullptr;
if (functions_to_process.count(func) == 0 || !builtin) {
return;
}
if (builtin->Type() == sem::BuiltinType::kTextureStore) {
// A call to textureStore() will always be a statement.
// Wrap it inside a conditional block.
auto* masked_call = b.If(b.Not(flag), b.Block(ctx.Clone(stmt->Declaration())));
ctx.Replace(stmt->Declaration(), masked_call);
} else if (builtin->IsAtomic() &&
builtin->Type() != sem::BuiltinType::kAtomicLoad) {
// A call to an atomic builtin can be a statement or an expression.
if (auto* call_stmt = stmt->Declaration()->As<ast::CallStatement>();
call_stmt && call_stmt->expr == call) {
// This call is a statement.
// Wrap it inside a conditional block.
auto* masked_call = b.If(b.Not(flag), b.Block(ctx.Clone(call_stmt)));
ctx.Replace(stmt->Declaration(), masked_call);
} else {
// This call is an expression.
// We transform:
// let y = x + atomicAdd(&p, 1);
// Into:
// var tmp : i32;
// if (!tint_discarded) {
// tmp = atomicAdd(&p, 1);
// }
// let y = x + tmp;
auto result = b.Sym();
const ast::Type* result_ty = nullptr;
const ast::Statement* masked_call = nullptr;
if (builtin->Type() == sem::BuiltinType::kAtomicCompareExchangeWeak) {
// Special case for atomicCompareExchangeWeak as we cannot name its
// result type. We have to declare an equivalent struct and copy the
// original member values over to it.
// Declare a struct to hold the result values.
auto* result_struct = sem_call->Type()->As<sem::Struct>();
auto* atomic_ty = result_struct->Members()[0]->Type();
result_ty = b.ty.type_name(
utils::GetOrCreate(atomic_cmpxchg_result_types, atomic_ty, [&]() {
auto name = b.Sym();
b.Structure(
name,
utils::Vector{
b.Member("old_value", CreateASTTypeFor(ctx, atomic_ty)),
b.Member("exchanged", b.ty.bool_()),
});
return name;
}));
// Generate the masked call and member-wise copy:
// if (!tint_discarded) {
// let tmp_result = atomicCompareExchangeWeak(&p, 1, 2);
// result.exchanged = tmp_result.exchanged;
// result.old_value = tmp_result.old_value;
// }
auto tmp_result = b.Sym();
masked_call =
b.If(b.Not(flag),
b.Block(utils::Vector{
b.Decl(b.Let(tmp_result, ctx.CloneWithoutTransform(call))),
b.Assign(b.MemberAccessor(result, "old_value"),
b.MemberAccessor(tmp_result, "old_value")),
b.Assign(b.MemberAccessor(result, "exchanged"),
b.MemberAccessor(tmp_result, "exchanged")),
}));
} else {
result_ty = CreateASTTypeFor(ctx, sem_call->Type());
masked_call =
b.If(b.Not(flag),
b.Block(b.Assign(result, ctx.CloneWithoutTransform(call))));
}
auto* result_decl = b.Decl(b.Var(result, result_ty));
hoist_to_decl_before.Prepare(sem_call);
hoist_to_decl_before.InsertBefore(stmt, result_decl);
hoist_to_decl_before.InsertBefore(stmt, masked_call);
ctx.Replace(call, b.Expr(result));
}
}
},
// Insert a conditional discard before all return statements in entry points.
[&](const ast::ReturnStatement* ret) {
auto* func = sem.Get(ret)->Function();
if (func->Declaration()->IsEntryPoint() && functions_to_process.count(func)) {
auto* discard = b.If(flag, b.Block(b.Discard()));
ctx.InsertBefore(sem.Get(ret)->Block()->Declaration()->statements, ret,
discard);
}
});
}
ctx.Clone();
return Program(std::move(b));
}
} // namespace tint::transform