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// Copyright 2021 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/resolver/dependency_graph.h"
#include <string>
#include <unordered_set>
#include <utility>
#include <vector>
#include "src/ast/continue_statement.h"
#include "src/ast/discard_statement.h"
#include "src/ast/fallthrough_statement.h"
#include "src/ast/traverse_expressions.h"
#include "src/scope_stack.h"
#include "src/sem/builtin.h"
#include "src/utils/defer.h"
#include "src/utils/map.h"
#include "src/utils/scoped_assignment.h"
#include "src/utils/unique_vector.h"
#define TINT_DUMP_DEPENDENCY_GRAPH 0
namespace tint {
namespace resolver {
namespace {
// Forward declaration
struct Global;
/// Dependency describes how one global depends on another global
struct DependencyInfo {
/// The source of the symbol that forms the dependency
Source source;
/// A string describing how the dependency is referenced. e.g. 'calls'
const char* action = nullptr;
};
/// DependencyEdge describes the two Globals used to define a dependency
/// relationship.
struct DependencyEdge {
/// The Global that depends on #to
const Global* from;
/// The Global that is depended on by #from
const Global* to;
};
/// DependencyEdgeCmp implements the contracts of std::equal_to<DependencyEdge>
/// and std::hash<DependencyEdge>.
struct DependencyEdgeCmp {
/// Equality operator
bool operator()(const DependencyEdge& lhs, const DependencyEdge& rhs) const {
return lhs.from == rhs.from && lhs.to == rhs.to;
}
/// Hashing operator
inline std::size_t operator()(const DependencyEdge& d) const {
return utils::Hash(d.from, d.to);
}
};
/// A map of DependencyEdge to DependencyInfo
using DependencyEdges = std::unordered_map<DependencyEdge,
DependencyInfo,
DependencyEdgeCmp,
DependencyEdgeCmp>;
/// Global describes a module-scope variable, type or function.
struct Global {
explicit Global(const ast::Node* n) : node(n) {}
/// The declaration ast::Node
const ast::Node* node;
/// A list of dependencies that this global depends on
std::vector<Global*> deps;
};
/// A map of global name to Global
using GlobalMap = std::unordered_map<Symbol, Global*>;
/// Raises an ICE that a global ast::Node type was not handled by this system.
void UnhandledNode(diag::List& diagnostics, const ast::Node* node) {
TINT_ICE(Resolver, diagnostics)
<< "unhandled node type: " << node->TypeInfo().name;
}
/// Raises an error diagnostic with the given message and source.
void AddError(diag::List& diagnostics,
const std::string& msg,
const Source& source) {
diagnostics.add_error(diag::System::Resolver, msg, source);
}
/// Raises a note diagnostic with the given message and source.
void AddNote(diag::List& diagnostics,
const std::string& msg,
const Source& source) {
diagnostics.add_note(diag::System::Resolver, msg, source);
}
/// DependencyScanner is used to traverse a module to build the list of
/// global-to-global dependencies.
class DependencyScanner {
public:
/// Constructor
/// @param syms the program symbol table
/// @param globals_by_name map of global symbol to Global pointer
/// @param diagnostics diagnostic messages, appended with any errors found
/// @param graph the dependency graph to populate with resolved symbols
/// @param edges the map of globals-to-global dependency edges, which will
/// be populated by calls to Scan()
DependencyScanner(const SymbolTable& syms,
const GlobalMap& globals_by_name,
diag::List& diagnostics,
DependencyGraph& graph,
DependencyEdges& edges)
: symbols_(syms),
globals_(globals_by_name),
diagnostics_(diagnostics),
graph_(graph),
dependency_edges_(edges) {
// Register all the globals at global-scope
for (auto it : globals_by_name) {
scope_stack_.Set(it.first, it.second->node);
}
}
/// Walks the global declarations, resolving symbols, and determining the
/// dependencies of each global.
void Scan(Global* global) {
TINT_SCOPED_ASSIGNMENT(current_global_, global);
if (auto* str = global->node->As<ast::Struct>()) {
Declare(str->name, str);
for (auto* member : str->members) {
TraverseType(member->type);
}
return;
}
if (auto* alias = global->node->As<ast::Alias>()) {
Declare(alias->name, alias);
TraverseType(alias->type);
return;
}
if (auto* func = global->node->As<ast::Function>()) {
Declare(func->symbol, func);
TraverseAttributes(func->attributes);
TraverseFunction(func);
return;
}
if (auto* var = global->node->As<ast::Variable>()) {
Declare(var->symbol, var);
TraverseType(var->type);
if (var->constructor) {
TraverseExpression(var->constructor);
}
return;
}
UnhandledNode(diagnostics_, global->node);
}
private:
/// Traverses the function, performing symbol resolution and determining
/// global dependencies.
void TraverseFunction(const ast::Function* func) {
scope_stack_.Push();
TINT_DEFER(scope_stack_.Pop());
for (auto* param : func->params) {
if (auto* shadows = scope_stack_.Get(param->symbol)) {
graph_.shadows.emplace(param, shadows);
}
Declare(param->symbol, param);
TraverseType(param->type);
}
if (func->body) {
TraverseStatements(func->body->statements);
}
TraverseType(func->return_type);
}
/// Traverses the statements, performing symbol resolution and determining
/// global dependencies.
void TraverseStatements(const ast::StatementList& stmts) {
for (auto* s : stmts) {
TraverseStatement(s);
}
}
/// Traverses the statement, performing symbol resolution and determining
/// global dependencies.
void TraverseStatement(const ast::Statement* stmt) {
if (stmt == nullptr) {
return;
}
if (auto* b = stmt->As<ast::AssignmentStatement>()) {
TraverseExpression(b->lhs);
TraverseExpression(b->rhs);
return;
}
if (auto* b = stmt->As<ast::BlockStatement>()) {
scope_stack_.Push();
TINT_DEFER(scope_stack_.Pop());
TraverseStatements(b->statements);
return;
}
if (auto* r = stmt->As<ast::CallStatement>()) {
TraverseExpression(r->expr);
return;
}
if (auto* l = stmt->As<ast::ForLoopStatement>()) {
scope_stack_.Push();
TINT_DEFER(scope_stack_.Pop());
TraverseStatement(l->initializer);
TraverseExpression(l->condition);
TraverseStatement(l->continuing);
TraverseStatement(l->body);
return;
}
if (auto* l = stmt->As<ast::LoopStatement>()) {
scope_stack_.Push();
TINT_DEFER(scope_stack_.Pop());
TraverseStatements(l->body->statements);
TraverseStatement(l->continuing);
return;
}
if (auto* i = stmt->As<ast::IfStatement>()) {
TraverseExpression(i->condition);
TraverseStatement(i->body);
for (auto* e : i->else_statements) {
TraverseExpression(e->condition);
TraverseStatement(e->body);
}
return;
}
if (auto* r = stmt->As<ast::ReturnStatement>()) {
TraverseExpression(r->value);
return;
}
if (auto* s = stmt->As<ast::SwitchStatement>()) {
TraverseExpression(s->condition);
for (auto* c : s->body) {
for (auto* sel : c->selectors) {
TraverseExpression(sel);
}
TraverseStatement(c->body);
}
return;
}
if (auto* v = stmt->As<ast::VariableDeclStatement>()) {
if (auto* shadows = scope_stack_.Get(v->variable->symbol)) {
graph_.shadows.emplace(v->variable, shadows);
}
TraverseType(v->variable->type);
TraverseExpression(v->variable->constructor);
Declare(v->variable->symbol, v->variable);
return;
}
if (stmt->IsAnyOf<ast::BreakStatement, ast::ContinueStatement,
ast::DiscardStatement, ast::FallthroughStatement>()) {
return;
}
UnhandledNode(diagnostics_, stmt);
}
/// Adds the symbol definition to the current scope, raising an error if two
/// symbols collide within the same scope.
void Declare(Symbol symbol, const ast::Node* node) {
auto* old = scope_stack_.Set(symbol, node);
if (old != nullptr && node != old) {
auto name = symbols_.NameFor(symbol);
AddError(diagnostics_, "redeclaration of '" + name + "'", node->source);
AddNote(diagnostics_, "'" + name + "' previously declared here",
old->source);
}
}
/// Traverses the expression, performing symbol resolution and determining
/// global dependencies.
void TraverseExpression(const ast::Expression* root) {
if (!root) {
return;
}
ast::TraverseExpressions(
root, diagnostics_, [&](const ast::Expression* expr) {
if (auto* ident = expr->As<ast::IdentifierExpression>()) {
auto* node = scope_stack_.Get(ident->symbol);
if (node == nullptr) {
if (!IsBuiltin(ident->symbol)) {
UnknownSymbol(ident->symbol, ident->source, "identifier");
}
return ast::TraverseAction::Descend;
}
auto global_it = globals_.find(ident->symbol);
if (global_it != globals_.end() &&
node == global_it->second->node) {
AddGlobalDependency(ident, ident->symbol, "identifier",
"references");
} else {
graph_.resolved_symbols.emplace(ident, node);
}
}
if (auto* call = expr->As<ast::CallExpression>()) {
if (call->target.name) {
if (!IsBuiltin(call->target.name->symbol)) {
AddGlobalDependency(call->target.name,
call->target.name->symbol, "function",
"calls");
graph_.resolved_symbols.emplace(
call,
utils::Lookup(graph_.resolved_symbols, call->target.name));
}
}
if (call->target.type) {
TraverseType(call->target.type);
graph_.resolved_symbols.emplace(
call,
utils::Lookup(graph_.resolved_symbols, call->target.type));
}
}
if (auto* cast = expr->As<ast::BitcastExpression>()) {
TraverseType(cast->type);
}
return ast::TraverseAction::Descend;
});
}
/// Traverses the type node, performing symbol resolution and determining
/// global dependencies.
void TraverseType(const ast::Type* ty) {
if (ty == nullptr) {
return;
}
if (auto* arr = ty->As<ast::Array>()) {
TraverseType(arr->type);
TraverseExpression(arr->count);
return;
}
if (auto* atomic = ty->As<ast::Atomic>()) {
TraverseType(atomic->type);
return;
}
if (auto* mat = ty->As<ast::Matrix>()) {
TraverseType(mat->type);
return;
}
if (auto* ptr = ty->As<ast::Pointer>()) {
TraverseType(ptr->type);
return;
}
if (auto* tn = ty->As<ast::TypeName>()) {
AddGlobalDependency(tn, tn->name, "type", "references");
return;
}
if (auto* vec = ty->As<ast::Vector>()) {
TraverseType(vec->type);
return;
}
if (auto* tex = ty->As<ast::SampledTexture>()) {
TraverseType(tex->type);
return;
}
if (auto* tex = ty->As<ast::MultisampledTexture>()) {
TraverseType(tex->type);
return;
}
if (ty->IsAnyOf<ast::Void, ast::Bool, ast::I32, ast::U32, ast::F32,
ast::DepthTexture, ast::DepthMultisampledTexture,
ast::StorageTexture, ast::ExternalTexture,
ast::Sampler>()) {
return;
}
UnhandledNode(diagnostics_, ty);
}
/// Traverses the attribute list, performing symbol resolution and
/// determining global dependencies.
void TraverseAttributes(const ast::AttributeList& attrs) {
for (auto* attr : attrs) {
TraverseAttribute(attr);
}
}
/// Traverses the attribute, performing symbol resolution and determining
/// global dependencies.
void TraverseAttribute(const ast::Attribute* attr) {
if (auto* wg = attr->As<ast::WorkgroupAttribute>()) {
TraverseExpression(wg->x);
TraverseExpression(wg->y);
TraverseExpression(wg->z);
return;
}
if (attr->IsAnyOf<
ast::BindingAttribute, ast::BuiltinAttribute, ast::GroupAttribute,
ast::InternalAttribute, ast::InterpolateAttribute,
ast::InvariantAttribute, ast::LocationAttribute,
ast::OverrideAttribute, ast::StageAttribute, ast::StrideAttribute,
ast::StructBlockAttribute, ast::StructMemberAlignAttribute,
ast::StructMemberOffsetAttribute,
ast::StructMemberSizeAttribute>()) {
return;
}
UnhandledNode(diagnostics_, attr);
}
/// Adds the dependency to the currently processed global
void AddGlobalDependency(const ast::Node* from,
Symbol to,
const char* use,
const char* action) {
auto global_it = globals_.find(to);
if (global_it != globals_.end()) {
auto* global = global_it->second;
if (dependency_edges_
.emplace(DependencyEdge{current_global_, global},
DependencyInfo{from->source, action})
.second) {
current_global_->deps.emplace_back(global);
}
graph_.resolved_symbols.emplace(from, global->node);
} else {
UnknownSymbol(to, from->source, use);
}
}
/// @returns true if `name` is the name of a builtin function
bool IsBuiltin(Symbol name) const {
return sem::ParseBuiltinType(symbols_.NameFor(name)) !=
sem::BuiltinType::kNone;
}
/// Appends an error to the diagnostics that the given symbol cannot be
/// resolved.
void UnknownSymbol(Symbol name, Source source, const char* use) {
AddError(
diagnostics_,
"unknown " + std::string(use) + ": '" + symbols_.NameFor(name) + "'",
source);
}
using VariableMap = std::unordered_map<Symbol, const ast::Variable*>;
const SymbolTable& symbols_;
const GlobalMap& globals_;
diag::List& diagnostics_;
DependencyGraph& graph_;
DependencyEdges& dependency_edges_;
ScopeStack<const ast::Node*> scope_stack_;
Global* current_global_ = nullptr;
};
/// The global dependency analysis system
struct DependencyAnalysis {
public:
/// Constructor
DependencyAnalysis(const SymbolTable& symbols,
diag::List& diagnostics,
DependencyGraph& graph)
: symbols_(symbols), diagnostics_(diagnostics), graph_(graph) {}
/// Performs global dependency analysis on the module, emitting any errors to
/// #diagnostics.
/// @returns true if analysis found no errors, otherwise false.
bool Run(const ast::Module& module, bool allow_out_of_order_decls) {
// Collect all the named globals from the AST module
GatherGlobals(module);
// Traverse the named globals to build the dependency graph
DetermineDependencies();
// Sort the globals into dependency order
SortGlobals();
// Dump the dependency graph if TINT_DUMP_DEPENDENCY_GRAPH is non-zero
DumpDependencyGraph();
if (!allow_out_of_order_decls) {
// Prevent out-of-order declarations.
ErrorOnOutOfOrderDeclarations();
}
graph_.ordered_globals = std::move(sorted_);
return !diagnostics_.contains_errors();
}
private:
/// @param node the ast::Node of the global declaration
/// @returns the symbol of the global declaration node
/// @note will raise an ICE if the node is not a type, function or variable
/// declaration
Symbol SymbolOf(const ast::Node* node) const {
if (auto* td = node->As<ast::TypeDecl>()) {
return td->name;
}
if (auto* func = node->As<ast::Function>()) {
return func->symbol;
}
if (auto* var = node->As<ast::Variable>()) {
return var->symbol;
}
UnhandledNode(diagnostics_, node);
return {};
}
/// @param node the ast::Node of the global declaration
/// @returns the name of the global declaration node
/// @note will raise an ICE if the node is not a type, function or variable
/// declaration
std::string NameOf(const ast::Node* node) const {
return symbols_.NameFor(SymbolOf(node));
}
/// @param node the ast::Node of the global declaration
/// @returns a string representation of the global declaration kind
/// @note will raise an ICE if the node is not a type, function or variable
/// declaration
std::string KindOf(const ast::Node* node) {
if (node->Is<ast::Struct>()) {
return "struct";
}
if (node->Is<ast::Alias>()) {
return "alias";
}
if (node->Is<ast::Function>()) {
return "function";
}
if (auto* var = node->As<ast::Variable>()) {
return var->is_const ? "let" : "var";
}
UnhandledNode(diagnostics_, node);
return {};
}
/// Traverses `module`, collecting all the global declarations and populating
/// the #globals and #declaration_order fields.
void GatherGlobals(const ast::Module& module) {
for (auto* node : module.GlobalDeclarations()) {
auto* global = allocator_.Create(node);
globals_.emplace(SymbolOf(node), global);
declaration_order_.emplace_back(global);
}
}
/// Walks the global declarations, determining the dependencies of each global
/// and adding these to each global's Global::deps field.
void DetermineDependencies() {
DependencyScanner scanner(symbols_, globals_, diagnostics_, graph_,
dependency_edges_);
for (auto* global : declaration_order_) {
scanner.Scan(global);
}
}
/// Performs a depth-first traversal of `root`'s dependencies, calling `enter`
/// as the function decends into each dependency and `exit` when bubbling back
/// up towards the root.
/// @param enter is a function with the signature: `bool(Global*)`. The
/// `enter` function returns true if TraverseDependencies() should traverse
/// the dependency, otherwise it will be skipped.
/// @param exit is a function with the signature: `void(Global*)`. The `exit`
/// function is only called if the corresponding `enter` call returned true.
template <typename ENTER, typename EXIT>
void TraverseDependencies(const Global* root, ENTER&& enter, EXIT&& exit) {
// Entry is a single entry in the traversal stack. Entry points to a
// dep_idx'th dependency of Entry::global.
struct Entry {
const Global* global; // The parent global
size_t dep_idx; // The dependency index in `global->deps`
};
if (!enter(root)) {
return;
}
std::vector<Entry> stack{Entry{root, 0}};
while (true) {
auto& entry = stack.back();
// Have we exhausted the dependencies of entry.global?
if (entry.dep_idx < entry.global->deps.size()) {
// No, there's more dependencies to traverse.
auto& dep = entry.global->deps[entry.dep_idx];
// Does the caller want to enter this dependency?
if (enter(dep)) { // Yes.
stack.push_back(Entry{dep, 0}); // Enter the dependency.
} else {
entry.dep_idx++; // No. Skip this node.
}
} else {
// Yes. Time to back up.
// Exit this global, pop the stack, and if there's another parent node,
// increment its dependency index, and loop again.
exit(entry.global);
stack.pop_back();
if (stack.empty()) {
return; // All done.
}
stack.back().dep_idx++;
}
}
}
/// SortGlobals sorts the globals into dependency order, erroring if cyclic
/// dependencies are found. The sorted dependencies are assigned to #sorted.
void SortGlobals() {
if (diagnostics_.contains_errors()) {
return; // This code assumes there are no undeclared identifiers.
}
std::unordered_set<const Global*> visited;
for (auto* global : declaration_order_) {
utils::UniqueVector<const Global*> stack;
TraverseDependencies(
global,
[&](const Global* g) { // Enter
if (!stack.add(g)) {
CyclicDependencyFound(g, stack);
return false;
}
if (sorted_.contains(g->node)) {
// Visited this global already.
// stack was pushed, but exit() will not be called when we return
// false, so pop here.
stack.pop_back();
return false;
}
return true;
},
[&](const Global* g) { // Exit. Only called if Enter returned true.
sorted_.add(g->node);
stack.pop_back();
});
sorted_.add(global->node);
if (!stack.empty()) {
// Each stack.push() must have a corresponding stack.pop_back().
TINT_ICE(Resolver, diagnostics_)
<< "stack not empty after returning from TraverseDependencies()";
}
}
}
/// DepInfoFor() looks up the global dependency information for the dependency
/// of global `from` depending on `to`.
/// @note will raise an ICE if the edge is not found.
DependencyInfo DepInfoFor(const Global* from, const Global* to) const {
auto it = dependency_edges_.find(DependencyEdge{from, to});
if (it != dependency_edges_.end()) {
return it->second;
}
TINT_ICE(Resolver, diagnostics_)
<< "failed to find dependency info for edge: '" << NameOf(from->node)
<< "' -> '" << NameOf(to->node) << "'";
return {};
}
// TODO(crbug.com/tint/1266): Errors if there are any uses of globals before
// their declaration. Out-of-order declarations was added to the WGSL
// specification with https://github.com/gpuweb/gpuweb/pull/2244, but Mozilla
// have objections to this change so this feature is currently disabled via
// this function.
void ErrorOnOutOfOrderDeclarations() {
if (diagnostics_.contains_errors()) {
// Might have already errored about cyclic dependencies. No need to report
// out-of-order errors as well.
return;
}
std::unordered_set<const Global*> seen;
for (auto* global : declaration_order_) {
for (auto* dep : global->deps) {
if (!seen.count(dep)) {
auto info = DepInfoFor(global, dep);
auto name = NameOf(dep->node);
AddError(diagnostics_,
KindOf(dep->node) + " '" + name +
"' used before it has been declared",
info.source);
AddNote(diagnostics_,
KindOf(dep->node) + " '" + name + "' declared here",
dep->node->source);
}
}
seen.emplace(global);
}
}
/// CyclicDependencyFound() emits an error diagnostic for a cyclic dependency.
/// @param root is the global that starts the cyclic dependency, which must be
/// found in `stack`.
/// @param stack is the global dependency stack that contains a loop.
void CyclicDependencyFound(const Global* root,
const std::vector<const Global*>& stack) {
std::stringstream msg;
msg << "cyclic dependency found: ";
constexpr size_t kLoopNotStarted = ~0u;
size_t loop_start = kLoopNotStarted;
for (size_t i = 0; i < stack.size(); i++) {
auto* e = stack[i];
if (loop_start == kLoopNotStarted && e == root) {
loop_start = i;
}
if (loop_start != kLoopNotStarted) {
msg << "'" << NameOf(e->node) << "' -> ";
}
}
msg << "'" << NameOf(root->node) << "'";
AddError(diagnostics_, msg.str(), root->node->source);
for (size_t i = loop_start; i < stack.size(); i++) {
auto* from = stack[i];
auto* to = (i + 1 < stack.size()) ? stack[i + 1] : stack[loop_start];
auto info = DepInfoFor(from, to);
AddNote(diagnostics_,
KindOf(from->node) + " '" + NameOf(from->node) + "' " +
info.action + " " + KindOf(to->node) + " '" +
NameOf(to->node) + "' here",
info.source);
}
}
void DumpDependencyGraph() {
#if TINT_DUMP_DEPENDENCY_GRAPH == 0
if ((true)) {
return;
}
#endif // TINT_DUMP_DEPENDENCY_GRAPH
printf("=========================\n");
printf("------ declaration ------ \n");
for (auto* global : declaration_order_) {
printf("%s\n", NameOf(global->node).c_str());
}
printf("------ dependencies ------ \n");
for (auto* node : sorted_) {
auto symbol = SymbolOf(node);
auto* global = globals_.at(symbol);
printf("%s depends on:\n", symbols_.NameFor(symbol).c_str());
for (auto* dep : global->deps) {
printf(" %s\n", NameOf(dep->node).c_str());
}
}
printf("=========================\n");
}
/// Program symbols
const SymbolTable& symbols_;
/// Program diagnostics
diag::List& diagnostics_;
/// The resulting dependency graph
DependencyGraph& graph_;
/// Allocator of Globals
BlockAllocator<Global> allocator_;
/// Global map, keyed by name. Populated by GatherGlobals().
GlobalMap globals_;
/// Map of DependencyEdge to DependencyInfo. Populated by
/// DetermineDependencies().
DependencyEdges dependency_edges_;
/// Globals in declaration order. Populated by GatherGlobals().
std::vector<Global*> declaration_order_;
/// Globals in sorted dependency order. Populated by SortGlobals().
utils::UniqueVector<const ast::Node*> sorted_;
};
} // namespace
DependencyGraph::DependencyGraph() = default;
DependencyGraph::DependencyGraph(DependencyGraph&&) = default;
DependencyGraph::~DependencyGraph() = default;
bool DependencyGraph::Build(const ast::Module& module,
const SymbolTable& symbols,
diag::List& diagnostics,
DependencyGraph& output,
bool allow_out_of_order_decls) {
DependencyAnalysis da{symbols, diagnostics, output};
return da.Run(module, allow_out_of_order_decls);
}
} // namespace resolver
} // namespace tint