Consolidate br_on* operations (#5399)

The `br_on{_non}_{data,i31,func}` operations are deprecated and directly
representable in terms of the new `br_on_cast` and `br_on_cast_fail`
instructions, so remove their dedicated IR opcodes in favor of representing them
as casts. `br_on_null` and `br_on_non_null` cannot be consolidated the same way
because their behavior is not directly representable in terms of `br_on_cast`
and `br_on_cast_fail`; when the cast to null bottom type succeeds, the null
check instructions implicitly drop the null value whereas the cast instructions
would propagate it.

Add special logic to the binary writer and printer to continue emitting the
deprecated instructions for now. This will allow us to update the test suite in
a separate future PR with no additional functional changes.

Some tests are updated because the validator no longer allows passing non-func
data to `br_on_func`. Doing so has not made sense since we separated the three
reference type hierarchies.

1 files changed, 14 insertions, 4 deletions

diff --git a/src/wasm/wasm-s-parser.cpp b/src/wasm/wasm-s-parser.cpp
index fd3cbcc23..638dfbebf 100644
--- a/src/wasm/wasm-s-parser.cpp
+++ b/src/wasm/wasm-s-parser.cpp
@@ -2818,11 +2818,20 @@ Expression* SExpressionWasmBuilder::makeRefCastNop(Element& s) {
   return Builder(wasm).makeRefCast(ref, type, RefCast::Unsafe);
 }
 
-Expression* SExpressionWasmBuilder::makeBrOn(Element& s, BrOnOp op) {
+Expression* SExpressionWasmBuilder::makeBrOnNull(Element& s, bool onFail) {
   int i = 1;
   auto name = getLabel(*s[i++]);
-  Type castType = Type::none;
-  if (op == BrOnCast || op == BrOnCastFail) {
+  auto* ref = parseExpression(*s[i]);
+  auto op = onFail ? BrOnNonNull : BrOnNull;
+  return Builder(wasm).makeBrOn(op, name, ref);
+}
+
+Expression* SExpressionWasmBuilder::makeBrOnCast(Element& s,
+                                                 std::optional<Type> castType,
+                                                 bool onFail) {
+  int i = 1;
+  auto name = getLabel(*s[i++]);
+  if (!castType) {
     auto nullability = NonNullable;
     if (s[i]->str().str == "null") {
       nullability = Nullable;
@@ -2832,7 +2841,8 @@ Expression* SExpressionWasmBuilder::makeBrOn(Element& s, BrOnOp op) {
     castType = Type(type, nullability);
   }
   auto* ref = parseExpression(*s[i]);
-  return Builder(wasm).makeBrOn(op, name, ref, castType);
+  auto op = onFail ? BrOnCastFail : BrOnCast;
+  return Builder(wasm).makeBrOn(op, name, ref, *castType);
 }
 
 Expression* SExpressionWasmBuilder::makeStructNew(Element& s, bool default_) {