Optimize wasm reading (#1202)

* optimize wasm reading: use a set of the breaks we've seen, don't rescan blocks to see if they have breaks to them

Author: kripken

src/wasm-binary.h

@@ -863,6 +863,7 @@ class WasmBinaryBuilder {
     BreakTarget(Name name, int arity) : name(name), arity(arity) {}
   };
   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

@@ -1629,6 +1629,7 @@ void WasmBinaryBuilder::readFunctions() {
       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());
@@ -1637,6 +1638,7 @@ void WasmBinaryBuilder::readFunctions() {
       assert(depth == 0);
       assert(breakStack.size() == 1);
       breakStack.pop_back();
+      assert(breakTargetNames.size() == 0);
       if (!expressionStack.empty()) {
         throw ParseException("stack not empty on function exit");
       }
@@ -2222,6 +2224,7 @@ void WasmBinaryBuilder::visitBlock(Block *curr) {
     pushBlockElements(curr, start, end);
     curr->finalize(curr->type);
     breakStack.pop_back();
+    breakTargetNames.erase(curr->name);
   }
 }
 
@@ -2237,12 +2240,13 @@ Expression* WasmBinaryBuilder::getBlockOrSingleton(WasmType type) {
   block->name = label;
   block->finalize(type);
   // maybe we don't need a block here?
-  if (!brokenTo(block)) {
+  if (breakTargetNames.find(block->name) == breakTargetNames.end()) {
     block->name = Name();
     if (block->list.size() == 1) {
       return block->list[0];
     }
   }
+  breakTargetNames.erase(block->name);
   return block;
 }
 
@@ -2285,6 +2289,7 @@ void WasmBinaryBuilder::visitLoop(Loop *curr) {
     curr->body = block;
   }
   breakStack.pop_back();
+  breakTargetNames.erase(curr->name);
   curr->finalize(curr->type);
 }
 
@@ -2301,7 +2306,9 @@ WasmBinaryBuilder::BreakTarget WasmBinaryBuilder::getBreakTarget(int32_t offset)
     breaksToReturn = true;
   }
   if (debug) std::cerr << "breaktarget "<< breakStack[index].name << " arity " << breakStack[index].arity <<  std::endl;
-  return breakStack[index];
+  auto& ret = breakStack[index];
+  breakTargetNames.insert(ret.name);
+  return ret;
 }
 
 void WasmBinaryBuilder::visitBreak(Break *curr, uint8_t code) {