Fix reading breaks to the function exit (#1304)

* remove unneeded code to handle a br to the return from the function. Now that we use getBlockOrSingleton there, it does that for us anyhow

Author: kripken

src/wasm-binary.h

@@ -864,7 +864,6 @@ class WasmBinaryBuilder {
   };
   std::vector<BreakTarget> breakStack;
   std::unordered_set<Name> breakTargetNames;
-  bool breaksToReturn; // whether a break is done to the function scope, which is in effect a return
 
   std::vector<Expression*> expressionStack;
 

src/wasm/wasm-binary.cpp

@@ -1204,8 +1204,6 @@ void WasmBinaryWriter::visitDrop(Drop *curr) {
 
 // reader
 
-static Name RETURN_BREAK("binaryen|break-to-return");
-
 void WasmBinaryBuilder::read() {
 
   readHeader();
@@ -1626,28 +1624,21 @@ void WasmBinaryBuilder::readFunctions() {
       if (debug) std::cerr << "processing function: " << i << std::endl;
       nextLabel = 0;
       useDebugLocation = false;
-      breaksToReturn = false;
       // process body
       assert(breakTargetNames.size() == 0);
       assert(breakStack.empty());
-      breakStack.emplace_back(RETURN_BREAK, func->result != none); // the break target for the function scope
       assert(expressionStack.empty());
       assert(depth == 0);
       func->body = getBlockOrSingleton(func->result);
       assert(depth == 0);
-      assert(breakStack.size() == 1);
-      breakStack.pop_back();
+      assert(breakStack.size() == 0);
       assert(breakTargetNames.size() == 0);
       if (!expressionStack.empty()) {
         throw ParseException("stack not empty on function exit");
       }
       if (pos != endOfFunction) {
         throw ParseException("binary offset at function exit not at expected location");
       }
-      if (breaksToReturn) {
-        // we broke to return, so we need an outer block to break to
-        func->body = Builder(wasm).blockifyWithName(func->body, RETURN_BREAK);
-      }
     }
     currFunction = nullptr;
     functions.push_back(func);
@@ -2325,15 +2316,12 @@ void WasmBinaryBuilder::visitLoop(Loop *curr) {
 
 WasmBinaryBuilder::BreakTarget WasmBinaryBuilder::getBreakTarget(int32_t offset) {
   if (debug) std::cerr << "getBreakTarget " << offset << std::endl;
+  if (breakStack.size() < 1 + size_t(offset)) {
+    throw ParseException("bad breakindex (low)");
+  }
   size_t index = breakStack.size() - 1 - offset;
   if (index >= breakStack.size()) {
-    throw ParseException("bad breakindex");
-  }
-  if (index == 0) {
-    // trying to access the topmost element means we break out
-    // to the function scope, doing in effect a return, we'll
-    // need to create a block for that.
-    breaksToReturn = true;
+    throw ParseException("bad breakindex (high)");
   }
   if (debug) std::cerr << "breaktarget "<< breakStack[index].name << " arity " << breakStack[index].arity <<  std::endl;
   auto& ret = breakStack[index];

test/br_to_exit.wasm

@@ -0,0 +1,10 @@
+(module
+ (type $0 (func))
+ (memory $0 0)
+ (func $0 (; 0 ;) (type $0)
+  (block $label$0
+   (br $label$0)
+  )
+ )
+)
+