handle continues in one-time loops

1 files changed, 30 insertions, 18 deletions

diff --git a/src/asm2wasm.h b/src/asm2wasm.h
index 06960a114..c13c847e7 100644
--- a/src/asm2wasm.h
+++ b/src/asm2wasm.h
@@ -66,6 +66,17 @@ struct AstStackHelper {
 
 std::vector<Ref> AstStackHelper::astStack;
 
+struct BreakSeeker : public WasmWalker<BreakSeeker> {
+  IString target; // look for this one
+  size_t found;
+
+  BreakSeeker(IString target) : target(target), found(false) {}
+
+  void visitBreak(Break *curr) {
+    if (curr->name == target) found++;
+  }
+};
+
 //
 // Asm2WasmPreProcessor - does some initial parsing/processing
 // of asm.js code.
@@ -1281,8 +1292,7 @@ Function* Asm2WasmBuilder::processFunction(Ref ast) {
       return ret;
     } else if (what == DO) {
       if (ast[1][0] == NUM && ast[1][1]->getNumber() == 0) {
-        // one-time loop
-        auto block = allocator.alloc<Block>();
+        // one-time loop, unless there is a continue
         IString stop;
         if (!parentLabel.isNull()) {
           stop = getBreakLabelName(parentLabel);
@@ -1290,13 +1300,27 @@ Function* Asm2WasmBuilder::processFunction(Ref ast) {
         } else {
           stop = getNextId("do-once");
         }
-        block->name = stop;
+        IString more = getNextId("unlikely-continue");
         breakStack.push_back(stop);
-        continueStack.push_back(IMPOSSIBLE_CONTINUE);
-        block->list.push_back(process(ast[2]));
+        continueStack.push_back(more);
+        auto child = process(ast[2]);
         continueStack.pop_back();
         breakStack.pop_back();
-        return block;
+        // if we never continued, we don't need a loop
+        BreakSeeker breakSeeker(more);
+        breakSeeker.walk(child);
+        if (breakSeeker.found == 0) {
+          auto block = allocator.alloc<Block>();
+          block->list.push_back(child);
+          block->name = stop;
+          return block;
+        } else {
+          auto loop = allocator.alloc<Loop>();
+          loop->body = child;
+          loop->out = stop;
+          loop->in = more;
+          return loop;
+        }
       }
       // general do-while loop
       auto ret = allocator.alloc<Loop>();
@@ -1514,18 +1538,6 @@ void Asm2WasmBuilder::optimize() {
         return;
       }
       // we might be broken to, but maybe there isn't a break (and we may have removed it, leading to this)
-
-      struct BreakSeeker : public WasmWalker<BreakSeeker> {
-        IString target; // look for this one
-        size_t found;
-
-        BreakSeeker(IString target) : target(target), found(false) {}
-
-        void visitBreak(Break *curr) {
-          if (curr->name == target) found++;
-        }
-      };
-
       // look for any breaks to this block
       BreakSeeker breakSeeker(curr->name);
       Expression *child = curr->list[0];