feat: implement tail call optimization

src/passes/CMakeLists.txt

@@ -114,6 +114,7 @@ set(passes_SOURCES
   ReorderGlobals.cpp
   ReorderLocals.cpp
   ReReloop.cpp
+  TailCall.cpp
   TrapMode.cpp
   TypeGeneralizing.cpp
   TypeRefining.cpp

src/passes/TailCall.cpp

@@ -0,0 +1,82 @@
+
+#include "pass.h"
+#include "wasm-traversal.h"
+#include "wasm.h"
+#include <vector>
+
+namespace wasm {
+
+namespace {
+
+struct Finder : PostWalker<Finder> {
+  std::vector<Call*> tailCalls;
+  std::vector<CallIndirect*> tailCallIndirects;
+  void visitFunction(Function* curr) { checkTailCall(curr->body); }
+  void visitReturn(Return* curr) { checkTailCall(curr->value); }
+
+private:
+  void checkTailCall(Expression* expr) {
+    if (expr == nullptr) {
+      return;
+    }
+    if (auto* call = expr->dynCast<Call>()) {
+      if (!call->isReturn && call->type == getFunction()->getResults()) {
+        tailCalls.push_back(call);
+      }
+      return;
+    }
+    if (auto* call = expr->dynCast<CallIndirect>()) {
+      if (!call->isReturn && call->type == getFunction()->getResults()) {
+        tailCallIndirects.push_back(call);
+      }
+      return;
+    }
+    if (auto* block = expr->dynCast<Block>()) {
+      return checkTailCall(block->list);
+    }
+    if (auto* ifElse = expr->dynCast<If>()) {
+      checkTailCall(ifElse->ifTrue);
+      checkTailCall(ifElse->ifFalse);
+      return;
+    }
+  }
+  void checkTailCall(ExpressionList const& exprs) {
+    if (exprs.empty()) {
+      return;
+    }
+    checkTailCall(exprs.back());
+    return;
+  }
+};
+
+} // namespace
+
+struct TailCallOptimizer : public Pass {
+  bool isFunctionParallel() override { return true; }
+  std::unique_ptr<Pass> create() override {
+    return std::make_unique<TailCallOptimizer>();
+  }
+  void runOnFunction(Module* module, Function* function) override {
+    if (!module->features.hasTailCall()) {
+      return;
+    }
+    Finder finder{};
+    finder.walkFunctionInModule(function, module);
+    for (Call* call : finder.tailCalls) {
+      if (!call->isReturn) {
+        call->isReturn = true;
+        call->finalize();
+      }
+    }
+    for (CallIndirect* call : finder.tailCallIndirects) {
+      if (!call->isReturn) {
+        call->isReturn = true;
+        call->finalize();
+      }
+    }
+  }
+};
+
+Pass* createTailCallPass() { return new TailCallOptimizer(); }
+
+} // namespace wasm

src/passes/pass.cpp

@@ -552,6 +552,8 @@ void PassRegistry::registerPasses() {
   registerPass("strip-target-features",
                "strip the wasm target features section",
                createStripTargetFeaturesPass);
+  registerPass(
+    "tail-call", "transform call to return call", createTailCallPass);
   registerPass("translate-to-new-eh",
                "deprecated; same as translate-to-exnref",
                createTranslateToExnrefPass);

src/passes/passes.h

@@ -176,6 +176,7 @@ Pass* createStripEHPass();
 Pass* createStubUnsupportedJSOpsPass();
 Pass* createSSAifyPass();
 Pass* createSSAifyNoMergePass();
+Pass* createTailCallPass();
 Pass* createTable64LoweringPass();
 Pass* createTranslateToExnrefPass();
 Pass* createTrapModeClamp();