src/tint/transform/spirv_atomic.cc

// 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/spirv_atomic.h"

#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

#include "src/tint/program_builder.h"
#include "src/tint/sem/block_statement.h"
#include "src/tint/sem/function.h"
#include "src/tint/sem/index_accessor_expression.h"
#include "src/tint/sem/member_accessor_expression.h"
#include "src/tint/sem/reference.h"
#include "src/tint/sem/statement.h"
#include "src/tint/utils/map.h"
#include "src/tint/utils/unique_vector.h"

TINT_INSTANTIATE_TYPEINFO(tint::transform::SpirvAtomic);
TINT_INSTANTIATE_TYPEINFO(tint::transform::SpirvAtomic::Stub);

namespace tint::transform {

/// Private implementation of transform
struct SpirvAtomic::State {
  private:
    /// A struct that has been forked because a subset of members were made atomic.
    struct ForkedStruct {
        Symbol name;
        std::unordered_set<size_t> atomic_members;
    };

    CloneContext& ctx;
    ProgramBuilder& b = *ctx.dst;
    std::unordered_map<const ast::Struct*, ForkedStruct> forked_structs;
    std::unordered_set<const sem::Variable*> atomic_variables;
    utils::UniqueVector<const sem::Expression*> atomic_expressions;

  public:
    /// Constructor
    /// @param c the clone context
    explicit State(CloneContext& c) : ctx(c) {}

    /// Runs the transform
    void Run() {
        // Look for stub functions generated by the SPIR-V reader, which are used as placeholders
        // for atomic builtin calls.
        for (auto* fn : ctx.src->AST().Functions()) {
            if (auto* stub = ast::GetAttribute<Stub>(fn->attributes)) {
                auto* sem = ctx.src->Sem().Get(fn);

                for (auto* call : sem->CallSites()) {
                    // The first argument is always the atomic.
                    // The stub passes this by value, whereas the builtin wants a pointer.
                    // Take the address of the atomic argument.
                    auto& args = call->Declaration()->args;
                    auto out_args = ctx.Clone(args);
                    out_args[0] = b.AddressOf(out_args[0]);

                    // Replace all callsites of this stub to a call to the real builtin
                    if (stub->builtin == sem::BuiltinType::kAtomicCompareExchangeWeak) {
                        // atomicCompareExchangeWeak returns a struct, so insert a call to it above
                        // the current statement, and replace the current call with the struct's
                        // `old_value` member.
                        auto* block = call->Stmt()->Block()->Declaration();
                        auto old_value = b.Symbols().New("old_value");
                        auto old_value_decl = b.Decl(b.Let(
                            old_value, nullptr,
                            b.MemberAccessor(b.Call(sem::str(stub->builtin), std::move(out_args)),
                                             b.Expr("old_value"))));
                        ctx.InsertBefore(block->statements, call->Stmt()->Declaration(),
                                         old_value_decl);
                        ctx.Replace(call->Declaration(), b.Expr(old_value));
                    } else {
                        ctx.Replace(call->Declaration(),
                                    b.Call(sem::str(stub->builtin), std::move(out_args)));
                    }

                    // Keep track of this expression. We'll need to modify the source variable /
                    // structure to be atomic.
                    atomic_expressions.add(ctx.src->Sem().Get(args[0]));
                }

                // Remove the stub from the output program
                ctx.Remove(ctx.src->AST().GlobalDeclarations(), fn);
            }
        }

        // Transform all variables and structure members that were used in atomic operations as
        // atomic types. This propagates up originating expression chains.
        ProcessAtomicExpressions();

        // If we need to change structure members, then fork them.
        if (!forked_structs.empty()) {
            ctx.ReplaceAll([&](const ast::Struct* str) {
                // Always emit the original structure. This allows unrelated usage of the structure
                // to continue working.
                // auto* original = ctx.CloneWithoutTransform(str);

                // Is `str` a structure we need to fork?
                if (auto it = forked_structs.find(str); it != forked_structs.end()) {
                    const auto& forked = it->second;

                    // Re-create the structure swapping in the atomic-flavoured members
                    std::vector<const ast::StructMember*> members(str->members.size());
                    for (size_t i = 0; i < str->members.size(); i++) {
                        auto* member = str->members[i];
                        if (forked.atomic_members.count(i)) {
                            auto* type = AtomicTypeFor(ctx.src->Sem().Get(member)->Type());
                            auto name = ctx.src->Symbols().NameFor(member->symbol);
                            members[i] = b.Member(name, type, ctx.Clone(member->attributes));
                        } else {
                            members[i] = ctx.Clone(member);
                        }
                    }
                    b.Structure(forked.name, std::move(members));
                }

                // return original;
                return nullptr;
            });
        }

        ctx.Clone();
    }

  private:
    ForkedStruct& Fork(const ast::Struct* str) {
        auto& forked = forked_structs[str];
        if (!forked.name.IsValid()) {
            forked.name = b.Symbols().New(ctx.src->Symbols().NameFor(str->name) + "_atomic");
        }
        return forked;
    }

    void ProcessAtomicExpressions() {
        for (size_t i = 0; i < atomic_expressions.size(); i++) {
            Switch(
                atomic_expressions[i],  //
                [&](const sem::VariableUser* user) {
                    auto* v = user->Variable()->Declaration();
                    if (v->type && atomic_variables.emplace(user->Variable()).second) {
                        ctx.Replace(v->type, AtomicTypeFor(user->Variable()->Type()));
                    }
                    if (auto* ctor = user->Variable()->Constructor()) {
                        atomic_expressions.add(ctor);
                    }
                },
                [&](const sem::StructMemberAccess* access) {
                    // Fork the struct (the first time) and mark member(s) that need to be made
                    // atomic.
                    auto* member = access->Member();
                    Fork(member->Struct()->Declaration()).atomic_members.emplace(member->Index());
                    atomic_expressions.add(access->Object());
                },
                [&](const sem::IndexAccessorExpression* index) {
                    atomic_expressions.add(index->Object());
                },
                [&](const sem::Expression* e) {
                    if (auto* unary = e->Declaration()->As<ast::UnaryOpExpression>()) {
                        atomic_expressions.add(ctx.src->Sem().Get(unary->expr));
                    }
                });
        }
    }

    const ast::Type* AtomicTypeFor(const sem::Type* ty) {
        return Switch(
            ty,  //
            [&](const sem::I32*) { return b.ty.atomic(CreateASTTypeFor(ctx, ty)); },
            [&](const sem::U32*) { return b.ty.atomic(CreateASTTypeFor(ctx, ty)); },
            [&](const sem::Struct* str) { return b.ty.type_name(Fork(str->Declaration()).name); },
            [&](const sem::Array* arr) {
                return arr->IsRuntimeSized()
                           ? b.ty.array(AtomicTypeFor(arr->ElemType()))
                           : b.ty.array(AtomicTypeFor(arr->ElemType()), u32(arr->Count()));
            },
            [&](const sem::Pointer* ptr) {
                return b.ty.pointer(AtomicTypeFor(ptr->StoreType()), ptr->StorageClass(),
                                    ptr->Access());
            },
            [&](const sem::Reference* ref) { return AtomicTypeFor(ref->StoreType()); },
            [&](Default) {
                TINT_ICE(Transform, b.Diagnostics())
                    << "unhandled type: " << ty->FriendlyName(ctx.src->Symbols());
                return nullptr;
            });
    }
};

SpirvAtomic::SpirvAtomic() = default;
SpirvAtomic::~SpirvAtomic() = default;

SpirvAtomic::Stub::Stub(ProgramID pid, sem::BuiltinType b) : Base(pid), builtin(b) {}
SpirvAtomic::Stub::~Stub() = default;
std::string SpirvAtomic::Stub::InternalName() const {
    return "@internal(spirv-atomic " + std::string(sem::str(builtin)) + ")";
}

const SpirvAtomic::Stub* SpirvAtomic::Stub::Clone(CloneContext* ctx) const {
    return ctx->dst->ASTNodes().Create<SpirvAtomic::Stub>(ctx->dst->ID(), builtin);
}

bool SpirvAtomic::ShouldRun(const Program* program, const DataMap&) const {
    for (auto* fn : program->AST().Functions()) {
        if (ast::HasAttribute<Stub>(fn->attributes)) {
            return true;
        }
    }
    return false;
}

void SpirvAtomic::Run(CloneContext& ctx, const DataMap&, DataMap&) const {
    State{ctx}.Run();
}

}  // namespace tint::transform