[NFC] Use indexes in DeadArgumentElimination (WebAssembly#7868)

Using vectors indexed by function makes this pass 15% faster on
large testcases. Previously we were doing a great number of
hashtable inserts using function names.

Author: kripken

src/passes/DeadArgumentElimination.cpp

@@ -189,6 +189,11 @@ struct DAE : public Pass {
 
   bool optimize = false;
 
+  Index numFunctions;
+
+  // Map of function names to indexes. This lets us use indexes below for speed.
+  std::unordered_map<Name, Index> indexes;
+
   void run(Module* module) override {
     DAEFunctionInfoMap infoMap;
     // Ensure all entries exist so the parallel threads don't modify the data
@@ -199,6 +204,12 @@ struct DAE : public Pass {
     // The null name represents module-level code (not in a function).
     infoMap[Name()];
 
+    numFunctions = module->functions.size();
+
+    for (Index i = 0; i < numFunctions; i++) {
+      indexes[module->functions[i]->name] = i;
+    }
+
     // Iterate to convergence.
     while (1) {
       if (!iteration(module, infoMap)) {
@@ -234,34 +245,36 @@ struct DAE : public Pass {
       Call* call;
       Function* func;
     };
-    std::map<Name, std::vector<Call*>> allCalls;
-    std::unordered_set<Name> tailCallees;
-    std::unordered_set<Name> hasUnseenCalls;
+
+    std::vector<std::vector<Call*>> allCalls(numFunctions);
+    std::vector<bool> tailCallees(numFunctions);
+    std::vector<bool> hasUnseenCalls(numFunctions);
+
     // Track the function in which relevant expressions exist. When we modify
     // those expressions we will need to mark the function's info as stale.
     std::unordered_map<Expression*, Name> expressionFuncs;
     for (auto& [func, info] : infoMap) {
       for (auto& [name, calls] : info.calls) {
-        auto& allCallsToName = allCalls[name];
+        auto& allCallsToName = allCalls[indexes[name]];
         allCallsToName.insert(allCallsToName.end(), calls.begin(), calls.end());
         for (auto* call : calls) {
           expressionFuncs[call] = func;
         }
       }
       for (auto& callee : info.tailCallees) {
-        tailCallees.insert(callee);
+        tailCallees[indexes[callee]] = true;
       }
       for (auto& [call, dropp] : info.droppedCalls) {
         allDroppedCalls[call] = dropp;
       }
       for (auto& name : info.hasUnseenCalls) {
-        hasUnseenCalls.insert(name);
+        hasUnseenCalls[indexes[name]] = true;
       }
     }
     // Exports are considered unseen calls.
     for (auto& curr : module->exports) {
       if (curr->kind == ExternalKind::Function) {
-        hasUnseenCalls.insert(*curr->getInternalName());
+        hasUnseenCalls[indexes[*curr->getInternalName()]] = true;
       }
     }
 
@@ -300,23 +313,32 @@ struct DAE : public Pass {
 
     // We now have a mapping of all call sites for each function, and can look
     // for optimization opportunities.
-    for (auto& [name, calls] : allCalls) {
+    for (Index index = 0; index < numFunctions; index++) {
+      auto* func = module->functions[index].get();
+      if (func->imported()) {
+        continue;
+      }
       // We can only optimize if we see all the calls and can modify them.
-      if (hasUnseenCalls.count(name)) {
+      if (hasUnseenCalls[index]) {
+        continue;
+      }
+      auto& calls = allCalls[index];
+      if (calls.empty()) {
+        // Nothing calls this, so it is not worth optimizing.
         continue;
       }
-      auto* func = module->getFunction(name);
       // Refine argument types before doing anything else. This does not
       // affect whether an argument is used or not, it just refines the type
       // where possible.
+      auto name = func->name;
       if (refineArgumentTypes(func, calls, module, infoMap[name])) {
         worthOptimizing.insert(func);
         markStale(func->name);
       }
       // Refine return types as well.
       if (refineReturnTypes(func, calls, module)) {
         refinedReturnTypes = true;
-        markStale(func->name);
+        markStale(name);
         markCallersStale(calls);
       }
       auto optimizedIndexes =
@@ -337,21 +359,29 @@ struct DAE : public Pass {
       ReFinalize().run(getPassRunner(), module);
     }
     // We now know which parameters are unused, and can potentially remove them.
-    for (auto& [name, calls] : allCalls) {
-      if (hasUnseenCalls.count(name)) {
+    for (Index index = 0; index < numFunctions; index++) {
+      auto* func = module->functions[index].get();
+      if (func->imported()) {
+        continue;
+      }
+      if (hasUnseenCalls[index]) {
         continue;
       }
-      auto* func = module->getFunction(name);
       auto numParams = func->getNumParams();
       if (numParams == 0) {
         continue;
       }
+      auto& calls = allCalls[index];
+      if (calls.empty()) {
+        continue;
+      }
+      auto name = func->name;
       auto [removedIndexes, outcome] = ParamUtils::removeParameters(
         {func}, infoMap[name].unusedParams, calls, {}, module, getPassRunner());
       if (!removedIndexes.empty()) {
         // Success!
         worthOptimizing.insert(func);
-        markStale(func->name);
+        markStale(name);
         markCallersStale(calls);
       }
       if (outcome == ParamUtils::RemovalOutcome::Failure) {
@@ -363,25 +393,28 @@ struct DAE : public Pass {
     // modified allCalls (we can't modify a call site twice in one iteration,
     // once to remove a param, once to drop the return value).
     if (worthOptimizing.empty()) {
-      for (auto& func : module->functions) {
+      for (Index index = 0; index < numFunctions; index++) {
+        auto& func = module->functions[index];
+        if (func->imported()) {
+          continue;
+        }
         if (func->getResults() == Type::none) {
           continue;
         }
-        auto name = func->name;
-        if (hasUnseenCalls.count(name)) {
+        if (hasUnseenCalls[index]) {
           continue;
         }
+        auto name = func->name;
         if (infoMap[name].hasTailCalls) {
           continue;
         }
-        if (tailCallees.count(name)) {
+        if (tailCallees[index]) {
           continue;
         }
-        auto iter = allCalls.find(name);
-        if (iter == allCalls.end()) {
+        auto& calls = allCalls[index];
+        if (calls.empty()) {
           continue;
         }
-        auto& calls = iter->second;
         bool allDropped =
           std::all_of(calls.begin(), calls.end(), [&](Call* call) {
             return allDroppedCalls.count(call);
@@ -398,7 +431,7 @@ struct DAE : public Pass {
         // TODO Removing a drop may also open optimization opportunities in the
         // callers.
         worthOptimizing.insert(func.get());
-        markStale(func->name);
+        markStale(name);
         markCallersStale(calls);
       }
     }