src/tint/lang/spirv/reader/ast_lower/pass_workgroup_id_as_argument.cc

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#include "src/tint/lang/spirv/reader/ast_lower/pass_workgroup_id_as_argument.h"

#include <utility>

#include "src/tint/lang/wgsl/program/clone_context.h"
#include "src/tint/lang/wgsl/program/program_builder.h"
#include "src/tint/lang/wgsl/resolver/resolve.h"
#include "src/tint/lang/wgsl/sem/function.h"
#include "src/tint/lang/wgsl/sem/statement.h"
#include "src/tint/utils/containers/hashmap.h"

using namespace tint::core::fluent_types;  // NOLINT

TINT_INSTANTIATE_TYPEINFO(tint::spirv::reader::PassWorkgroupIdAsArgument);

namespace tint::spirv::reader {

/// PIMPL state for the transform.
struct PassWorkgroupIdAsArgument::State {
    /// The source program
    const Program& src;
    /// The target program builder
    ProgramBuilder b;
    /// The clone context
    program::CloneContext ctx = {&b, &src, /* auto_clone_symbols */ true};
    /// The semantic info.
    const sem::Info& sem = src.Sem();

    /// Map from function to the name of its workgroup_id parameter.
    Hashmap<const ast::Function*, Symbol, 8> func_to_param;

    /// Constructor
    /// @param program the source program
    explicit State(const Program& program) : src(program) {}

    /// Runs the transform.
    /// @returns the new program
    ApplyResult Run() {
        // Process all entry points in the module, looking for workgroup_id builtin parameters.
        bool made_changes = false;
        for (auto* func : src.AST().Functions()) {
            if (func->IsEntryPoint()) {
                for (auto* param : func->params) {
                    if (auto* builtin =
                            ast::GetAttribute<ast::BuiltinAttribute>(param->attributes)) {
                        if (sem.Get(builtin)->Value() == core::BuiltinValue::kWorkgroupId) {
                            ProcessBuiltin(func, param);
                            made_changes = true;
                        }
                    }
                }
            }
        }
        if (!made_changes) {
            return SkipTransform;
        }

        ctx.Clone();
        return resolver::Resolve(b);
    }

    /// Process a workgroup_id builtin.
    /// @param ep the entry point function
    /// @param builtin the builtin parameter
    void ProcessBuiltin(const ast::Function* ep, const ast::Parameter* builtin) {
        // Record the name of the parameter for the entry point function.
        func_to_param.Add(ep, ctx.Clone(builtin->name->symbol));

        // The reader should only produce a single use of the parameter which assigns to a global.
        const auto& users = sem.Get(builtin)->Users();
        TINT_ASSERT_OR_RETURN(users.Length() == 1u);
        auto* assign = users[0]->Stmt()->Declaration()->As<ast::AssignmentStatement>();
        auto& stmts =
            sem.Get(assign)->Parent()->Declaration()->As<ast::BlockStatement>()->statements;
        auto* rhs = assign->rhs;
        if (auto* bitcast = rhs->As<ast::BitcastExpression>()) {
            // The RHS may be bitcast to a signed integer, so we capture that bitcast.
            auto let = b.Symbols().New("tint_wgid_bitcast");
            ctx.InsertBefore(stmts, assign, b.Decl(b.Let(let, ctx.Clone(bitcast))));
            func_to_param.Replace(ep, let);
            rhs = bitcast->expr;
        }
        TINT_ASSERT_OR_RETURN(assign && rhs == users[0]->Declaration());
        auto* lhs = sem.GetVal(assign->lhs)->As<sem::VariableUser>();
        TINT_ASSERT_OR_RETURN(lhs &&
                              lhs->Variable()->AddressSpace() == core::AddressSpace::kPrivate);

        // Replace all references to the global variable with a function parameter.
        for (auto* user : lhs->Variable()->Users()) {
            if (user == lhs) {
                // Skip the assignment, which will be removed.
                continue;
            }
            auto param = GetParameter(user->Stmt()->Function()->Declaration(),
                                      lhs->Variable()->Declaration()->type);
            ctx.Replace(user->Declaration(), b.Expr(param));
        }

        // Remove the global variable and the assignment to it.
        ctx.Remove(src.AST().GlobalDeclarations(), lhs->Variable()->Declaration());
        ctx.Remove(stmts, assign);
    }

    /// Get the workgroup_id parameter for a function, creating it and updating callsites if needed.
    /// @param func the function
    /// @param type the type of the parameter
    /// @returns the name of the parameter
    Symbol GetParameter(const ast::Function* func, const ast::Type& type) {
        return func_to_param.GetOrCreate(func, [&] {
            // Append a new parameter to the function.
            auto name = b.Symbols().New("tint_wgid");
            ctx.InsertBack(func->params, b.Param(name, ctx.Clone(type)));

            // Recursively update all callsites to pass the workgroup_id as an argument.
            for (auto* callsite : sem.Get(func)->CallSites()) {
                auto param = GetParameter(callsite->Stmt()->Function()->Declaration(), type);
                ctx.InsertBack(callsite->Declaration()->args, b.Expr(param));
            }

            return name;
        });
    }
};

PassWorkgroupIdAsArgument::PassWorkgroupIdAsArgument() = default;

PassWorkgroupIdAsArgument::~PassWorkgroupIdAsArgument() = default;

ast::transform::Transform::ApplyResult PassWorkgroupIdAsArgument::Apply(
    const Program& src,
    const ast::transform::DataMap&,
    ast::transform::DataMap&) const {
    return State(src).Run();
}

}  // namespace tint::spirv::reader