MergeSimilarFunctions: Do a return_call when possible (#7350)

This patch makes MergeSimilarFunctions do a return_call when the module
has tail-call enabled. This is not merely an optimization, but is
crucial for correctness when optimizing wasm modules produced by GHC
that relies on tail-call to do control flow transfers. Previously, -Oz
would break tail-call enabled modules by making the control stack grow
where it shouldn't.

Author: TerrorJack

src/passes/MergeSimilarFunctions.cpp

@@ -165,7 +165,8 @@ struct EquivalentClass {
                              Function* target,
                              Function* shared,
                              const std::vector<ParamInfo>& params,
-                             const std::vector<Expression*>& extraArgs);
+                             const std::vector<Expression*>& extraArgs,
+                             bool isReturn);
 
   bool deriveParams(Module* module,
                     std::vector<ParamInfo>& params,
@@ -480,7 +481,12 @@ void EquivalentClass::merge(Module* module,
     for (auto& param : params) {
       extraArgs.push_back(param.lowerToExpression(builder, module, i));
     }
-    replaceWithThunk(builder, func, sharedFn, params, extraArgs);
+    replaceWithThunk(builder,
+                     func,
+                     sharedFn,
+                     params,
+                     extraArgs,
+                     module->features.hasTailCall());
   }
   return;
 }
@@ -617,7 +623,8 @@ EquivalentClass::replaceWithThunk(Builder& builder,
                                   Function* target,
                                   Function* shared,
                                   const std::vector<ParamInfo>& params,
-                                  const std::vector<Expression*>& extraArgs) {
+                                  const std::vector<Expression*>& extraArgs,
+                                  bool isReturn) {
   std::vector<Expression*> callOperands;
   Type targetParams = target->getParams();
   for (Index i = 0; i < targetParams.size(); i++) {
@@ -628,8 +635,8 @@ EquivalentClass::replaceWithThunk(Builder& builder,
     callOperands.push_back(value);
   }
 
-  // TODO: make a return_call when possible?
-  auto ret = builder.makeCall(shared->name, callOperands, target->getResults());
+  auto ret = builder.makeCall(
+    shared->name, callOperands, target->getResults(), isReturn);
   target->vars.clear();
   target->body = ret;
   return target;

test/lit/passes/merge-similar-functions_all-features.wast

@@ -103,7 +103,7 @@
   ;; CHECK:      (elem declare func $return_a $return_b)
 
   ;; CHECK:      (func $return_call_a (type $0) (result i32)
-  ;; CHECK-NEXT:  (call $byn$mgfn-shared$return_call_a
+  ;; CHECK-NEXT:  (return_call $byn$mgfn-shared$return_call_a
   ;; CHECK-NEXT:   (ref.func $return_a)
   ;; CHECK-NEXT:  )
   ;; CHECK-NEXT: )
@@ -115,7 +115,7 @@
   )
 
   ;; CHECK:      (func $return_call_b (type $0) (result i32)
-  ;; CHECK-NEXT:  (call $byn$mgfn-shared$return_call_a
+  ;; CHECK-NEXT:  (return_call $byn$mgfn-shared$return_call_a
   ;; CHECK-NEXT:   (ref.func $return_b)
   ;; CHECK-NEXT:  )
   ;; CHECK-NEXT: )

test/lit/passes/merge-similar-functions_types.wast

@@ -17,7 +17,7 @@
  ;; CHECK:      (elem declare func $2 $3)
 
  ;; CHECK:      (func $0 (type $type$0)
- ;; CHECK-NEXT:  (call $byn$mgfn-shared$0
+ ;; CHECK-NEXT:  (return_call $byn$mgfn-shared$0
  ;; CHECK-NEXT:   (ref.func $2)
  ;; CHECK-NEXT:  )
  ;; CHECK-NEXT: )
@@ -41,7 +41,7 @@
   (nop)
  )
  ;; CHECK:      (func $1 (type $type$0)
- ;; CHECK-NEXT:  (call $byn$mgfn-shared$0
+ ;; CHECK-NEXT:  (return_call $byn$mgfn-shared$0
  ;; CHECK-NEXT:   (ref.func $3)
  ;; CHECK-NEXT:  )
  ;; CHECK-NEXT: )
@@ -126,7 +126,7 @@
  ;; CHECK:      (elem declare func $2 $3)
 
  ;; CHECK:      (func $0 (type $type$0)
- ;; CHECK-NEXT:  (call $byn$mgfn-shared$0
+ ;; CHECK-NEXT:  (return_call $byn$mgfn-shared$0
  ;; CHECK-NEXT:   (ref.func $2)
  ;; CHECK-NEXT:  )
  ;; CHECK-NEXT: )
@@ -150,7 +150,7 @@
   (nop)
  )
  ;; CHECK:      (func $1 (type $type$0)
- ;; CHECK-NEXT:  (call $byn$mgfn-shared$0
+ ;; CHECK-NEXT:  (return_call $byn$mgfn-shared$0
  ;; CHECK-NEXT:   (ref.func $3)
  ;; CHECK-NEXT:  )
  ;; CHECK-NEXT: )