wasm2js: remove more code we don't need since we have flat IR (#2039)

Also run remove-unused-names which became more noticeably necessary after this change.

Author: kripken

src/passes/I64ToI32Lowering.cpp

@@ -160,7 +160,6 @@ struct I64ToI32Lowering : public WalkerPass<PostWalker<I64ToI32Lowering>> {
     if (!builder) builder = make_unique<Builder>(*getModule());
     indexMap.clear();
     highBitVars.clear();
-    labelHighBitVars.clear();
     freeTemps.clear();
     Module temp;
     auto* oldFunc = ModuleUtils::copyFunction(func, temp);
@@ -221,124 +220,6 @@ struct I64ToI32Lowering : public WalkerPass<PostWalker<I64ToI32Lowering>> {
     }
   }
 
-  void visitBlock(Block* curr) {
-    if (curr->list.size() == 0) return;
-    if (handleUnreachable(curr)) return;
-    if (curr->type == i64) curr->type = i32;
-    auto highBitsIt = labelHighBitVars.find(curr->name);
-    if (!hasOutParam(curr->list.back())) {
-      if (highBitsIt != labelHighBitVars.end()) {
-        setOutParam(curr, std::move(highBitsIt->second));
-      }
-      return;
-    }
-    TempVar lastHighBits = fetchOutParam(curr->list.back());
-    if (highBitsIt == labelHighBitVars.end() ||
-        highBitsIt->second == lastHighBits) {
-      setOutParam(curr, std::move(lastHighBits));
-      if (highBitsIt != labelHighBitVars.end()) {
-        labelHighBitVars.erase(highBitsIt);
-      }
-      return;
-    }
-    TempVar highBits = std::move(highBitsIt->second);
-    TempVar tmp = getTemp();
-    labelHighBitVars.erase(highBitsIt);
-    SetLocal* setLow = builder->makeSetLocal(tmp, curr->list.back());
-    SetLocal* setHigh = builder->makeSetLocal(
-      highBits,
-      builder->makeGetLocal(lastHighBits, i32)
-    );
-    GetLocal* getLow = builder->makeGetLocal(tmp, i32);
-    curr->list.back() = builder->blockify(setLow, setHigh, getLow);
-    setOutParam(curr, std::move(highBits));
-  }
-
-  void visitIf(If* curr) {
-    if (!hasOutParam(curr->ifTrue)) return;
-    assert(curr->ifFalse != nullptr && "Nullable ifFalse found");
-    TempVar highBits = fetchOutParam(curr->ifTrue);
-    TempVar falseBits = fetchOutParam(curr->ifFalse);
-    TempVar tmp = getTemp();
-    curr->type = i32;
-    curr->ifFalse = builder->blockify(
-      builder->makeSetLocal(tmp, curr->ifFalse),
-      builder->makeSetLocal(
-        highBits,
-        builder->makeGetLocal(falseBits, i32)
-      ),
-      builder->makeGetLocal(tmp, i32)
-    );
-    setOutParam(curr, std::move(highBits));
-  }
-
-  void visitLoop(Loop* curr) {
-    // TODO: in flat IR, no chance for an out param
-    assert(labelHighBitVars.find(curr->name) == labelHighBitVars.end());
-    if (curr->type != i64) return;
-    curr->type = i32;
-    setOutParam(curr, fetchOutParam(curr->body));
-  }
-
-  void visitBreak(Break* curr) {
-    // TODO: in flat IR, no chance for an out param
-    if (!hasOutParam(curr->value)) return;
-    assert(curr->value != nullptr);
-    TempVar valHighBits = fetchOutParam(curr->value);
-    auto blockHighBitsIt = labelHighBitVars.find(curr->name);
-    if (blockHighBitsIt == labelHighBitVars.end()) {
-      labelHighBitVars.emplace(curr->name, std::move(valHighBits));
-      curr->type = i32;
-      return;
-    }
-    TempVar blockHighBits = std::move(blockHighBitsIt->second);
-    TempVar tmp = getTemp();
-    SetLocal* setLow = builder->makeSetLocal(tmp, curr->value);
-    SetLocal* setHigh = builder->makeSetLocal(
-      blockHighBits,
-      builder->makeGetLocal(valHighBits, i32)
-    );
-    curr->value = builder->makeGetLocal(tmp, i32);
-    curr->type = i32;
-    replaceCurrent(builder->blockify(setLow, setHigh, curr));
-  }
-
-  void visitSwitch(Switch* curr) {
-    // TODO: in flat IR, no chance for an out param
-    if (!hasOutParam(curr->value)) return;
-    TempVar outParam = fetchOutParam(curr->value);
-    TempVar tmp = getTemp();
-    Expression* result = curr;
-    std::vector<Name> targets;
-    size_t blockID = 0;
-    auto processTarget = [&](Name target) -> Name {
-      auto labelIt = labelHighBitVars.find(target);
-      if (labelIt == labelHighBitVars.end()) {
-        labelHighBitVars.emplace(target, getTemp());
-        labelIt = labelHighBitVars.find(target);
-      }
-      Name newLabel("$i64toi32_" + std::string(target.c_str()) +
-                    "_" + std::to_string(blockID++));
-      Block* trampoline = builder->makeBlock(newLabel, result);
-      trampoline->type = i32;
-      result = builder->blockify(
-        builder->makeSetLocal(tmp, trampoline),
-        builder->makeSetLocal(
-          labelIt->second,
-          builder->makeGetLocal(outParam, i32)
-        ),
-        builder->makeBreak(target, builder->makeGetLocal(tmp, i32))
-      );
-      return newLabel;
-    };
-    for (auto target : curr->targets) {
-      targets.push_back(processTarget(target));
-    }
-    curr->targets.set(targets);
-    curr->default_ = processTarget(curr->default_);
-    replaceCurrent(result);
-  }
-
   template<typename T>
   using BuilderFunc = std::function<T*(std::vector<Expression*>&, Type)>;
 
@@ -1615,7 +1496,6 @@ struct I64ToI32Lowering : public WalkerPass<PostWalker<I64ToI32Lowering>> {
   std::unordered_map<Index, Index> indexMap;
   std::unordered_map<int, std::vector<Index>> freeTemps;
   std::unordered_map<Expression*, TempVar> highBitVars;
-  std::unordered_map<Name, TempVar> labelHighBitVars;
   std::unordered_map<Index, Type> tempTypes;
   std::unordered_set<Name> originallyI64Globals;
   Index nextTemp;

src/wasm2js.h

@@ -136,10 +136,7 @@ class Wasm2JSBuilder {
 
   // The second pass on an expression: process it fully, generating
   // JS
-  // @param result Whether the context we are in receives a value,
-  //               and its type, or if not, then we can drop our return,
-  //               if we have one.
-  Ref processFunctionBody(Module* m, Function* func, IString result);
+  Ref processFunctionBody(Module* m, Function* func);
 
   // Get a temp var.
   IString getTemp(Type type, Function* func) {
@@ -274,6 +271,7 @@ Ref Wasm2JSBuilder::processWasm(Module* wasm, Name funcName) {
   runner.add("flatten");
   runner.add("simplify-locals-notee-nostructure");
   runner.add("reorder-locals");
+  runner.add("remove-unused-names");
   runner.add("vacuum");
   runner.add("remove-unused-module-elements");
   runner.setDebug(flags.debug);
@@ -632,6 +630,7 @@ Ref Wasm2JSBuilder::processFunction(Module* m, Function* func, bool standaloneFu
     runner.add("flatten");
     runner.add("simplify-locals-notee-nostructure");
     runner.add("reorder-locals");
+    runner.add("remove-unused-names");
     runner.add("vacuum");
     runner.runOnFunction(func);
   }
@@ -665,7 +664,7 @@ Ref Wasm2JSBuilder::processFunction(Module* m, Function* func, bool standaloneFu
   size_t theVarIndex = ret[3]->size();
   ret[3]->push_back(theVar);
   // body
-  flattenAppend(ret, processFunctionBody(m, func, NO_RESULT));
+  flattenAppend(ret, processFunctionBody(m, func));
   // vars, including new temp vars
   for (Index i = func->getVarIndexBase(); i < func->getNumLocals(); i++) {
     ValueBuilder::appendToVar(
@@ -684,7 +683,7 @@ Ref Wasm2JSBuilder::processFunction(Module* m, Function* func, bool standaloneFu
   return ret;
 }
 
-Ref Wasm2JSBuilder::processFunctionBody(Module* m, Function* func, IString result) {
+Ref Wasm2JSBuilder::processFunctionBody(Module* m, Function* func) {
   struct ExpressionProcessor : public Visitor<ExpressionProcessor, Ref> {
     Wasm2JSBuilder* parent;
     IString result; // TODO: remove
@@ -741,14 +740,9 @@ Ref Wasm2JSBuilder::processFunctionBody(Module* m, Function* func, IString resul
     }
 
     Ref visitAndAssign(Expression* curr, IString result) {
+      assert(result != NO_RESULT);
       Ref ret = visit(curr, result);
-      // if it's not already a statement, then it's an expression, and we need to assign it
-      // (if it is a statement, it already assigns to the result var)
-      if (result != NO_RESULT) {
-        ret = ValueBuilder::makeStatement(
-            ValueBuilder::makeBinary(ValueBuilder::makeName(result), SET, ret));
-      }
-      return ret;
+      return ValueBuilder::makeStatement(ValueBuilder::makeBinary(ValueBuilder::makeName(result), SET, ret));
     }
 
     Ref visitAndAssign(Expression* curr, ScopedTemp& temp) {
@@ -768,10 +762,6 @@ Ref Wasm2JSBuilder::processFunctionBody(Module* m, Function* func, IString resul
       return ret;
     }
 
-    // For spooky return-at-a-distance/break-with-result, this tells us
-    // what the result var is for a specific label.
-    std::map<Name, IString> breakResults;
-
     // Breaks to the top of a loop should be emitted as continues, to that loop's main label
     std::unordered_set<Name> continueLabels;
 
@@ -782,7 +772,6 @@ Ref Wasm2JSBuilder::processFunctionBody(Module* m, Function* func, IString resul
     // Visitors
 
     Ref visitBlock(Block* curr) {
-      breakResults[curr->name] = result;
       Ref ret = ValueBuilder::makeBlock();
       size_t size = curr->list.size();
       auto noResults = result == NO_RESULT ? size : size-1;
@@ -799,20 +788,13 @@ Ref Wasm2JSBuilder::processFunctionBody(Module* m, Function* func, IString resul
     }
 
     Ref visitIf(If* curr) {
-      IString temp;
       Ref condition = visit(curr->condition, EXPRESSION_RESULT);
-      Ref ifTrue = ValueBuilder::makeStatement(visitAndAssign(curr->ifTrue, result));
+      Ref ifTrue = visit(curr->ifTrue, NO_RESULT);
       Ref ifFalse;
       if (curr->ifFalse) {
-        ifFalse = ValueBuilder::makeStatement(visitAndAssign(curr->ifFalse, result));
-      }
-      if (temp.isNull()) {
-        return ValueBuilder::makeIf(condition, ifTrue, ifFalse); // simple if
+        ifFalse = visit(curr->ifFalse, NO_RESULT);
       }
-      condition = blockify(condition);
-      // just add an if to the block
-      condition[1]->push_back(ValueBuilder::makeIf(ValueBuilder::makeName(temp), ifTrue, ifFalse));
-      return condition;
+      return ValueBuilder::makeIf(condition, ifTrue, ifFalse); // simple if
     }
 
     Ref visitLoop(Loop* curr) {
@@ -842,13 +824,7 @@ Ref Wasm2JSBuilder::processFunctionBody(Module* m, Function* func, IString resul
         fakeIf.ifTrue = &fakeBreak;
         return visit(&fakeIf, result);
       }
-      Ref theBreak = makeBreakOrContinue(curr->name);
-      if (!curr->value) return theBreak;
-      // generate the value, including assigning to the result, and then do the break
-      Ref ret = visitAndAssign(curr->value, breakResults[curr->name]);
-      ret = blockify(ret);
-      ret[1]->push_back(theBreak);
-      return ret;
+      return makeBreakOrContinue(curr->name);
     }
 
     Expression* defaultBody = nullptr; // default must be last in asm.js
@@ -1141,7 +1117,7 @@ Ref Wasm2JSBuilder::processFunctionBody(Module* m, Function* func, IString resul
     }
 
     Ref visitDrop(Drop* curr) {
-      return visitAndAssign(curr->value, result);
+      return visit(curr->value, NO_RESULT);
     }
 
     Ref visitConst(Const* curr) {
@@ -1587,7 +1563,7 @@ Ref Wasm2JSBuilder::processFunctionBody(Module* m, Function* func, IString resul
     }
   };
 
-  return ExpressionProcessor(this, m, func).visit(func->body, result);
+  return ExpressionProcessor(this, m, func).visit(func->body, NO_RESULT);
 }
 
 void Wasm2JSBuilder::addMemoryGrowthFuncs(Ref ast, Module* wasm) {

test/passes/flatten_i64-to-i32-lowering.txt

@@ -206,7 +206,7 @@
   (local $1 i32)
   (local $1$hi i32)
   (local $i64toi32_i32$0 i32)
-  (block
+  (block $label$1
    (unreachable)
    (unreachable)
   )

test/wasm2js/block.2asm.js

@@ -34,25 +34,19 @@ function asmFunc(global, env, buffer) {
  }
 
  function $3() {
-  block : {
-   dummy();
-   dummy();
-   dummy();
-   dummy();
-  }
-  block1 : {
-   dummy();
-   dummy();
-   dummy();
-  }
+  dummy();
+  dummy();
+  dummy();
+  dummy();
+  dummy();
+  dummy();
+  dummy();
   return 8 | 0;
  }
 
  function $4() {
-  block : {
-   dummy();
-   dummy();
-  }
+  dummy();
+  dummy();
   return 9 | 0;
  }
 

test/wasm2js/br.2asm.js

@@ -115,37 +115,28 @@ function asmFunc(global, env, buffer) {
  function $13() {
   var $0 = 0, $1_1 = 0, $3_1 = 0;
   block : {
-   loop_in : do {
-    $0 = 3;
-    break block;
-    break loop_in;
-   } while (1);
+   $0 = 3;
+   break block;
   }
   return $0 | 0;
  }
 
  function $14() {
   var $0 = 0, $1_1 = 0, $3_1 = 0;
   block : {
-   loop_in : do {
-    dummy();
-    $0 = 4;
-    break block;
-    break loop_in;
-   } while (1);
+   dummy();
+   $0 = 4;
+   break block;
   }
   return $0 | 0;
  }
 
  function $15() {
   var $0 = 0;
   block : {
-   loop_in : do {
-    dummy();
-    $0 = 5;
-    break block;
-    break loop_in;
-   } while (1);
+   dummy();
+   $0 = 5;
+   break block;
   }
   return $0 | 0;
  }