[Parser] Parse br_if correctly (WebAssembly#6202)

The new text parser and IRBuilder were previously not differentiating between
`br` and `br_if`. Handle `br_if` correctly by popping and assigning a condition.

Author: tlively

scripts/gen-s-parser.py

@@ -24,8 +24,8 @@
     ("if",             "makeIf(s)"),
     ("then",           "makeThenOrElse(s)"),
     ("else",           "makeThenOrElse(s)"),
-    ("br",             "makeBreak(s)"),
-    ("br_if",          "makeBreak(s)"),
+    ("br",             "makeBreak(s, false)"),
+    ("br_if",          "makeBreak(s, true)"),
     ("br_table",       "makeBreakTable(s)"),
     ("return",         "makeReturn(s)"),
     ("call",           "makeCall(s, /*isReturn=*/false)"),

src/gen-s-parser.inc

@@ -102,12 +102,12 @@ switch (buf[0]) {
       case 'r': {
         switch (buf[2]) {
           case '\0':
-            if (op == "br"sv) { return makeBreak(s); }
+            if (op == "br"sv) { return makeBreak(s, false); }
             goto parse_error;
           case '_': {
             switch (buf[3]) {
               case 'i':
-                if (op == "br_if"sv) { return makeBreak(s); }
+                if (op == "br_if"sv) { return makeBreak(s, true); }
                 goto parse_error;
               case 'o': {
                 switch (buf[6]) {
@@ -3749,15 +3749,15 @@ switch (buf[0]) {
     switch (buf[2]) {
       case '\0':
         if (op == "br"sv) {
-          CHECK_ERR(makeBreak(ctx, pos));
+          CHECK_ERR(makeBreak(ctx, pos, false));
           return Ok{};
         }
         goto parse_error;
       case '_': {
         switch (buf[3]) {
           case 'i':
             if (op == "br_if"sv) {
-              CHECK_ERR(makeBreak(ctx, pos));
+              CHECK_ERR(makeBreak(ctx, pos, true));
               return Ok{};
             }
             goto parse_error;

src/parser/contexts.h

@@ -411,7 +411,7 @@ struct NullInstrParserCtx {
   Result<> makeCallIndirect(Index, TableIdxT*, TypeUseT, bool) {
     return Ok{};
   }
-  Result<> makeBreak(Index, LabelIdxT) { return Ok{}; }
+  Result<> makeBreak(Index, LabelIdxT, bool) { return Ok{}; }
   Result<> makeSwitch(Index, const std::vector<LabelIdxT>&, LabelIdxT) {
     return Ok{};
   }
@@ -1586,8 +1586,8 @@ struct ParseDefsCtx : TypeParserCtx<ParseDefsCtx> {
     return withLoc(pos, irBuilder.makeCallIndirect(*t, type, isReturn));
   }
 
-  Result<> makeBreak(Index pos, Index label) {
-    return withLoc(pos, irBuilder.makeBreak(label));
+  Result<> makeBreak(Index pos, Index label, bool isConditional) {
+    return withLoc(pos, irBuilder.makeBreak(label, isConditional));
   }
 
   Result<>

src/parser/parsers.h

@@ -104,7 +104,7 @@ template<typename Ctx> Result<> makeMemoryFill(Ctx&, Index);
 template<typename Ctx> Result<> makePop(Ctx&, Index);
 template<typename Ctx> Result<> makeCall(Ctx&, Index, bool isReturn);
 template<typename Ctx> Result<> makeCallIndirect(Ctx&, Index, bool isReturn);
-template<typename Ctx> Result<> makeBreak(Ctx&, Index);
+template<typename Ctx> Result<> makeBreak(Ctx&, Index, bool isConditional);
 template<typename Ctx> Result<> makeBreakTable(Ctx&, Index);
 template<typename Ctx> Result<> makeReturn(Ctx&, Index);
 template<typename Ctx> Result<> makeRefNull(Ctx&, Index);
@@ -1432,10 +1432,11 @@ Result<> makeCallIndirect(Ctx& ctx, Index pos, bool isReturn) {
   return ctx.makeCallIndirect(pos, table.getPtr(), *type, isReturn);
 }
 
-template<typename Ctx> Result<> makeBreak(Ctx& ctx, Index pos) {
+template<typename Ctx>
+Result<> makeBreak(Ctx& ctx, Index pos, bool isConditional) {
   auto label = labelidx(ctx);
   CHECK_ERR(label);
-  return ctx.makeBreak(pos, *label);
+  return ctx.makeBreak(pos, *label, isConditional);
 }
 
 template<typename Ctx> Result<> makeBreakTable(Ctx& ctx, Index pos) {

src/wasm-ir-builder.h

@@ -87,7 +87,7 @@ class IRBuilder : public UnifiedExpressionVisitor<IRBuilder, Result<>> {
   [[nodiscard]] Result<> makeBlock(Name label, Type type);
   [[nodiscard]] Result<> makeIf(Name label, Type type);
   [[nodiscard]] Result<> makeLoop(Name label, Type type);
-  [[nodiscard]] Result<> makeBreak(Index label);
+  [[nodiscard]] Result<> makeBreak(Index label, bool isConditional);
   [[nodiscard]] Result<> makeSwitch(const std::vector<Index>& labels,
                                     Index defaultLabel);
   // Unlike Builder::makeCall, this assumes the function already exists.

src/wasm-s-parser.h

@@ -270,7 +270,7 @@ class SExpressionWasmBuilder {
   }
   enum class LabelType { Break, Exception };
   Name getLabel(Element& s, LabelType labelType = LabelType::Break);
-  Expression* makeBreak(Element& s);
+  Expression* makeBreak(Element& s, bool isConditional);
   Expression* makeBreakTable(Element& s);
   Expression* makeReturn(Element& s);
   Expression* makeRefNull(Element& s);

src/wasm/wasm-ir-builder.cpp

@@ -430,6 +430,11 @@ Result<Expression*> IRBuilder::getBranchValue(Name labelName,
 }
 
 Result<> IRBuilder::visitBreak(Break* curr, std::optional<Index> label) {
+  if (curr->condition) {
+    auto cond = pop();
+    CHECK_ERR(cond);
+    curr->condition = *cond;
+  }
   auto value = getBranchValue(curr->name, label);
   CHECK_ERR(value);
   curr->value = *value;
@@ -961,13 +966,15 @@ Result<> IRBuilder::makeLoop(Name label, Type type) {
   return visitLoopStart(loop);
 }
 
-Result<> IRBuilder::makeBreak(Index label) {
+Result<> IRBuilder::makeBreak(Index label, bool isConditional) {
   auto name = getLabelName(label);
   CHECK_ERR(name);
   Break curr;
   curr.name = *name;
+  // Use a dummy condition value if we need to pop a condition.
+  curr.condition = isConditional ? &curr : nullptr;
   CHECK_ERR(visitBreak(&curr, label));
-  push(builder.makeBreak(curr.name, curr.value));
+  push(builder.makeBreak(curr.name, curr.value, curr.condition));
   return Ok{};
 }
 

src/wasm/wasm-s-parser.cpp

@@ -2580,15 +2580,15 @@ Name SExpressionWasmBuilder::getLabel(Element& s, LabelType labelType) {
   }
 }
 
-Expression* SExpressionWasmBuilder::makeBreak(Element& s) {
+Expression* SExpressionWasmBuilder::makeBreak(Element& s, bool isConditional) {
   auto ret = allocator.alloc<Break>();
   size_t i = 1;
   ret->name = getLabel(*s[i]);
   i++;
   if (i == s.size()) {
     return ret;
   }
-  if (elementStartsWith(s, BR_IF)) {
+  if (isConditional) {
     if (i + 1 < s.size()) {
       ret->value = parseExpression(s[i]);
       i++;