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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/expand_compound_assignment.h"
#include <utility>
#include "src/tint/ast/compound_assignment_statement.h"
#include "src/tint/ast/increment_decrement_statement.h"
#include "src/tint/program_builder.h"
#include "src/tint/sem/block_statement.h"
#include "src/tint/sem/expression.h"
#include "src/tint/sem/for_loop_statement.h"
#include "src/tint/sem/statement.h"
#include "src/tint/transform/utils/hoist_to_decl_before.h"
TINT_INSTANTIATE_TYPEINFO(tint::transform::ExpandCompoundAssignment);
using namespace tint::number_suffixes; // NOLINT
namespace tint::transform {
namespace {
bool ShouldRun(const Program* program) {
for (auto* node : program->ASTNodes().Objects()) {
if (node->IsAnyOf<ast::CompoundAssignmentStatement, ast::IncrementDecrementStatement>()) {
return true;
}
}
return false;
}
} // namespace
/// PIMPL state for the transform
struct ExpandCompoundAssignment::State {
/// Constructor
/// @param context the clone context
explicit State(CloneContext& context) : ctx(context), b(*ctx.dst), hoist_to_decl_before(ctx) {}
/// Replace `stmt` with a regular assignment statement of the form:
/// lhs = lhs op rhs
/// The LHS expression will only be evaluated once, and any side effects will
/// be hoisted to `let` declarations above the assignment statement.
/// @param stmt the statement to replace
/// @param lhs the lhs expression from the source statement
/// @param rhs the rhs expression in the destination module
/// @param op the binary operator
void Expand(const ast::Statement* stmt,
const ast::Expression* lhs,
const ast::Expression* rhs,
ast::BinaryOp op) {
// Helper function to create the new LHS expression. This will be called
// twice when building the non-compound assignment statement, so must
// not produce expressions that cause side effects.
std::function<const ast::Expression*()> new_lhs;
// Helper function to create a variable that is a pointer to `expr`.
auto hoist_pointer_to = [&](const ast::Expression* expr) {
auto name = b.Sym();
auto* ptr = b.AddressOf(ctx.Clone(expr));
auto* decl = b.Decl(b.Let(name, ptr));
hoist_to_decl_before.InsertBefore(ctx.src->Sem().Get(stmt), decl);
return name;
};
// Helper function to hoist `expr` to a let declaration.
auto hoist_expr_to_let = [&](const ast::Expression* expr) {
auto name = b.Sym();
auto* decl = b.Decl(b.Let(name, ctx.Clone(expr)));
hoist_to_decl_before.InsertBefore(ctx.src->Sem().Get(stmt), decl);
return name;
};
// Helper function that returns `true` if the type of `expr` is a vector.
auto is_vec = [&](const ast::Expression* expr) {
return ctx.src->Sem().Get(expr)->Type()->UnwrapRef()->Is<sem::Vector>();
};
// Hoist the LHS expression subtree into local constants to produce a new
// LHS that we can evaluate twice.
// We need to special case compound assignments to vector components since
// we cannot take the address of a vector component.
auto* index_accessor = lhs->As<ast::IndexAccessorExpression>();
auto* member_accessor = lhs->As<ast::MemberAccessorExpression>();
if (lhs->Is<ast::IdentifierExpression>() ||
(member_accessor && member_accessor->structure->Is<ast::IdentifierExpression>())) {
// This is the simple case with no side effects, so we can just use the
// original LHS expression directly.
// Before:
// foo.bar += rhs;
// After:
// foo.bar = foo.bar + rhs;
new_lhs = [&]() { return ctx.Clone(lhs); };
} else if (index_accessor && is_vec(index_accessor->object)) {
// This is the case for vector component via an array accessor. We need
// to capture a pointer to the vector and also the index value.
// Before:
// v[idx()] += rhs;
// After:
// let vec_ptr = &v;
// let index = idx();
// (*vec_ptr)[index] = (*vec_ptr)[index] + rhs;
auto lhs_ptr = hoist_pointer_to(index_accessor->object);
auto index = hoist_expr_to_let(index_accessor->index);
new_lhs = [&, lhs_ptr, index]() { return b.IndexAccessor(b.Deref(lhs_ptr), index); };
} else if (member_accessor && is_vec(member_accessor->structure)) {
// This is the case for vector component via a member accessor. We just
// need to capture a pointer to the vector.
// Before:
// a[idx()].y += rhs;
// After:
// let vec_ptr = &a[idx()];
// (*vec_ptr).y = (*vec_ptr).y + rhs;
auto lhs_ptr = hoist_pointer_to(member_accessor->structure);
new_lhs = [&, lhs_ptr]() {
return b.MemberAccessor(b.Deref(lhs_ptr), ctx.Clone(member_accessor->member));
};
} else {
// For all other statements that may have side-effecting expressions, we
// just need to capture a pointer to the whole LHS.
// Before:
// a[idx()] += rhs;
// After:
// let lhs_ptr = &a[idx()];
// (*lhs_ptr) = (*lhs_ptr) + rhs;
auto lhs_ptr = hoist_pointer_to(lhs);
new_lhs = [&, lhs_ptr]() { return b.Deref(lhs_ptr); };
}
// Replace the statement with a regular assignment statement.
auto* value = b.create<ast::BinaryExpression>(op, new_lhs(), rhs);
ctx.Replace(stmt, b.Assign(new_lhs(), value));
}
private:
/// The clone context.
CloneContext& ctx;
/// The program builder.
ProgramBuilder& b;
/// The HoistToDeclBefore helper instance.
HoistToDeclBefore hoist_to_decl_before;
};
ExpandCompoundAssignment::ExpandCompoundAssignment() = default;
ExpandCompoundAssignment::~ExpandCompoundAssignment() = default;
Transform::ApplyResult ExpandCompoundAssignment::Apply(const Program* src,
const DataMap&,
DataMap&) const {
if (!ShouldRun(src)) {
return SkipTransform;
}
ProgramBuilder b;
CloneContext ctx{&b, src, /* auto_clone_symbols */ true};
State state(ctx);
for (auto* node : src->ASTNodes().Objects()) {
if (auto* assign = node->As<ast::CompoundAssignmentStatement>()) {
state.Expand(assign, assign->lhs, ctx.Clone(assign->rhs), assign->op);
} else if (auto* inc_dec = node->As<ast::IncrementDecrementStatement>()) {
// For increment/decrement statements, `i++` becomes `i = i + 1`.
auto op = inc_dec->increment ? ast::BinaryOp::kAdd : ast::BinaryOp::kSubtract;
state.Expand(inc_dec, inc_dec->lhs, ctx.dst->Expr(1_a), op);
}
}
ctx.Clone();
return Program(std::move(b));
}
} // namespace tint::transform