tint: Optimization: Pre-allocate the ast -> sem map.

Change-Id: I674fe31786b08153509b470d14844d50cb7c3d9c
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/96143
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>

src/tint/resolver/resolver.cc

@@ -103,6 +103,9 @@ bool Resolver::Resolve() {
         return false;
     }
 
+    // Pre-allocate the ast -> sem map with the total number of AST nodes.
+    builder_->Sem().Reserve(builder_->ASTNodes().Count());
+
     if (!DependencyGraph::Build(builder_->AST(), builder_->Symbols(), builder_->Diagnostics(),
                                 dependencies_)) {
         return false;

src/tint/sem/info.h

@@ -35,7 +35,7 @@ class Info {
     /// Placeholder type used by Get() to provide a default value for EXPLICIT_SEM
     using InferFromAST = std::nullptr_t;
 
-    /// Resolves to the return type of the Get() method given the desired sementic
+    /// Resolves to the return type of the Get() method given the desired semantic
     /// type and AST type.
     template <typename SEM, typename AST>
     using GetResultType =
@@ -55,6 +55,10 @@ class Info {
     /// @return this Program
     Info& operator=(Info&& rhs);
 
+    /// Pre-allocates the AST -> semantic node map to fit at least the given number of nodes.
+    /// @param num_ast_nodes the number of AST nodes to pre-allocate the map for.
+    void Reserve(size_t num_ast_nodes) { map_.reserve(num_ast_nodes); }
+
     /// Get looks up the semantic information for the AST node `node`.
     /// @param ast_node the AST node
     /// @returns a pointer to the semantic node if found, otherwise nullptr