[NFC] Use a lazy LocalGraph in Heap2Local (#6925)

That pass only cares about reference locals, and even among them, only ones
that we see a struct.new/array.new that flows through locals. This makes the
pass 40% faster.

1 files changed, 6 insertions, 8 deletions

diff --git a/src/passes/Heap2Local.cpp b/src/passes/Heap2Local.cpp
index 82a5e90bb..09a50eea8 100644
--- a/src/passes/Heap2Local.cpp
+++ b/src/passes/Heap2Local.cpp
@@ -198,15 +198,17 @@ enum class ParentChildInteraction : int8_t {
 struct EscapeAnalyzer {
   // To find what escapes, we need to follow where values flow, both up to
   // parents, and via branches, and through locals.
-  // TODO: for efficiency, only scan reference types in LocalGraph
-  const LocalGraph& localGraph;
+  //
+  // We use a lazy graph here because we only need this for reference locals,
+  // and even among them, only ones we see an allocation is stored to.
+  const LazyLocalGraph& localGraph;
   const Parents& parents;
   const BranchUtils::BranchTargets& branchTargets;
 
   const PassOptions& passOptions;
   Module& wasm;
 
-  EscapeAnalyzer(const LocalGraph& localGraph,
+  EscapeAnalyzer(const LazyLocalGraph& localGraph,
                  const Parents& parents,
                  const BranchUtils::BranchTargets& branchTargets,
                  const PassOptions& passOptions,
@@ -1139,17 +1141,13 @@ struct Heap2Local {
   Module& wasm;
   const PassOptions& passOptions;
 
-  // TODO: construct this LocalGraph on demand
-  LocalGraph localGraph;
+  LazyLocalGraph localGraph;
   Parents parents;
   BranchUtils::BranchTargets branchTargets;
 
   Heap2Local(Function* func, Module& wasm, const PassOptions& passOptions)
     : func(func), wasm(wasm), passOptions(passOptions), localGraph(func, &wasm),
       parents(func->body), branchTargets(func->body) {
-    // We need to track what each set influences, to see where its value can
-    // flow to.
-    localGraph.computeSetInfluences();
 
     // Find all the relevant allocations in the function: StructNew, ArrayNew,
     // ArrayNewFixed.