3 files changed, 35 insertions, 14 deletions

diff --git a/src/wasm-interpreter.h b/src/wasm-interpreter.h
index 3f69d36e5..e20d3a358 100644
--- a/src/wasm-interpreter.h
+++ b/src/wasm-interpreter.h
@@ -211,14 +211,19 @@ private:
       }
       Flow visitBreak(Break *curr) override {
         NOTE_ENTER("Break");
+        bool condition = true;
+        if (curr->condition) {
+          Flow flow = visit(curr->condition);
+          if (flow.breaking()) return flow;
+          condition = flow.value.getInteger();
+        }
+        Flow flow(curr->name);
         if (curr->value) {
-          Flow flow = visit(curr->value);
-          if (!flow.breaking()) {
-            flow.breakTo = curr->name;
-          }
-          return flow;
+          flow = visit(curr->value);
+          if (flow.breaking()) return flow;
+          flow.breakTo = curr->name;
         }
-        return Flow(curr->name);
+        return condition ? flow : Flow();
       }
       Flow visitSwitch(Switch *curr) override {
         NOTE_ENTER("Switch");
diff --git a/src/wasm-s-parser.h b/src/wasm-s-parser.h
index ec7d6c6dc..8fbedcbf2 100644
--- a/src/wasm-s-parser.h
+++ b/src/wasm-s-parser.h
@@ -32,6 +32,7 @@ IString MODULE("module"),
         CALL("call"),
         CALL_IMPORT("call_import"),
         CALL_INDIRECT("call_indirect"),
+        BR_IF("br_if"),
         INFINITY_("infinity"),
         NEG_INFINITY("-infinity"),
         NAN_("nan"),
@@ -989,16 +990,22 @@ private:
 
   Expression* makeBreak(Element& s) {
     auto ret = allocator.alloc<Break>();
-    if (s[1]->dollared()) {
-      ret->name = s[1]->str();
+    size_t i = 1;
+    if (s[0]->str() == BR_IF) {
+      ret->condition = parseExpression(s[i]);
+      i++;
+    }
+    if (s[i]->dollared()) {
+      ret->name = s[i]->str();
     } else {
       // offset, break to nth outside label
-      size_t offset = atol(s[1]->c_str());
+      size_t offset = atol(s[i]->c_str());
       assert(offset < labelStack.size());
       ret->name = labelStack[labelStack.size() - 1 - offset];
     }
-    if (s.size() == 3) {
-      ret->value = parseExpression(s[2]);
+    i++;
+    if (i < s.size()) {
+      ret->value = parseExpression(s[i]);
     }
     return ret;
   }
diff --git a/src/wasm.h b/src/wasm.h
index 49951c14a..eb4d69fd4 100644
--- a/src/wasm.h
+++ b/src/wasm.h
@@ -392,14 +392,22 @@ public:
 
 class Break : public Expression {
 public:
-  Break() : Expression(BreakId), value(nullptr) {}
+  Break() : Expression(BreakId), condition(nullptr), value(nullptr) {}
 
+  Expression *condition;
   Name name;
   Expression *value;
 
   std::ostream& doPrint(std::ostream &o, unsigned indent) {
-    printOpening(o, "br ") << name;
-    incIndent(o, indent);
+    if (condition) {
+      printOpening(o, "br_if");
+      incIndent(o, indent);
+      printFullLine(o, indent, condition);
+      doIndent(o, indent) << name << '\n';
+    } else {
+      printOpening(o, "br ") << name;
+      incIndent(o, indent);
+    }
     if (value) printFullLine(o, indent, value);
     return decIndent(o, indent);
   }
@@ -1261,6 +1269,7 @@ struct WasmWalker : public WasmVisitor<void> {
       }
       void visitLabel(Label *curr) override {}
       void visitBreak(Break *curr) override {
+        parent.walk(curr->condition);
         parent.walk(curr->value);
       }
       void visitSwitch(Switch *curr) override {