More unsubtyping for cont.bind (#8506)

We were missing a few type constraints for cont.bind. Add them, and also
add more thorough tests for all the stack switching instructions,
including the cases where the continuations are null. As a drive-by to
get these tests working, fix the parsing of resume and resume_throw* to
set the proper type arity when the input is null.

Author: tlively

src/ir/subtype-exprs.h

@@ -494,32 +494,42 @@ struct SubtypingDiscoverer : public OverriddenVisitor<SubType> {
                         curr->type.getHeapType().getContinuation().type);
   }
   void visitContBind(ContBind* curr) {
-    if (!curr->cont->type.isContinuation()) {
+    if (!curr->cont->type.isContinuation() || !curr->type.isContinuation()) {
       return;
     }
+    auto inType = curr->cont->type.getHeapType();
+    auto outType = curr->type.getHeapType();
+    auto sigIn = inType.getContinuation().type.getSignature();
+    auto sigOut = outType.getContinuation().type.getSignature();
+
     // Each of the bound arguments must remain subtypes of their expected
     // parameters.
-    auto params = curr->cont->type.getHeapType()
-                    .getContinuation()
-                    .type.getSignature()
-                    .params;
-    assert(curr->operands.size() <= params.size());
-    for (Index i = 0; i < curr->operands.size(); ++i) {
-      self()->noteSubtype(curr->operands[i], params[i]);
+    size_t numBound = curr->operands.size();
+    for (Index i = 0; i < numBound; ++i) {
+      self()->noteSubtype(curr->operands[i], sigIn.params[i]);
+    }
+    // Each of the unbound output parameters must remain subtypes of their
+    // corresponding input parameters.
+    size_t numRemaining = sigIn.params.size() - numBound;
+    for (Index i = 0; i < numRemaining; ++i) {
+      self()->noteSubtype(sigOut.params[i], sigIn.params[numBound + i]);
     }
+    // The original input results must remain a subtype of the new output
+    // results.
+    self()->noteSubtype(sigIn.results, sigOut.results);
   }
   void visitSuspend(Suspend* curr) {
+    auto sig = self()->getModule()->getTag(curr->tag)->type.getSignature();
     // The operands must remain subtypes of the parameters given by the tag.
-    auto params =
-      self()->getModule()->getTag(curr->tag)->type.getSignature().params;
-    assert(curr->operands.size() == params.size());
+    assert(curr->operands.size() == sig.params.size());
     for (Index i = 0; i < curr->operands.size(); ++i) {
-      self()->noteSubtype(curr->operands[i], params[i]);
+      self()->noteSubtype(curr->operands[i], sig.params[i]);
     }
   }
   void processResumeHandlers(Type contType,
                              const ArenaVector<Name>& handlerTags,
                              const ArenaVector<Name>& handlerBlocks) {
+    assert(contType.isContinuation());
     auto contSig = contType.getHeapType().getContinuation().type.getSignature();
     assert(handlerTags.size() == handlerBlocks.size());
     auto& wasm = *self()->getModule();

src/wasm-builder.h

@@ -1352,44 +1352,34 @@ class Builder {
                      const std::vector<Name>& handlerBlocks,
                      const std::vector<Type>& sentTypes,
                      ExpressionList&& operands,
-                     Expression* cont) {
+                     Expression* cont,
+                     HeapType contType) {
     auto* ret = wasm.allocator.alloc<Resume>();
     ret->handlerTags.set(handlerTags);
     ret->handlerBlocks.set(handlerBlocks);
     ret->sentTypes.set(sentTypes);
     ret->operands = std::move(operands);
     ret->cont = cont;
+    ret->type = contType.getContinuation().type.getSignature().results;
     ret->finalize();
     return ret;
   }
-  template<typename T>
-  Resume* makeResume(const std::vector<Name>& handlerTags,
-                     const std::vector<Name>& handlerBlocks,
-                     const std::vector<Type>& sentTypes,
-                     ExpressionList& operands,
-                     Expression* cont) {
-    auto* ret = wasm.allocator.alloc<Resume>();
-    ret->handlerTags.set(handlerTags);
-    ret->handlerBlocks.set(handlerBlocks);
-    ret->sentTypes.set(sentTypes);
-    ret->operands.set(operands);
-    ret->cont = cont;
-    ret->finalize();
-    return ret;
-  }
+
   ResumeThrow* makeResumeThrow(Name tag,
                                const std::vector<Name>& handlerTags,
                                const std::vector<Name>& handlerBlocks,
                                const std::vector<Type>& sentTypes,
                                ExpressionList&& operands,
-                               Expression* cont) {
+                               Expression* cont,
+                               HeapType contType) {
     auto* ret = wasm.allocator.alloc<ResumeThrow>();
     ret->tag = tag;
     ret->handlerTags.set(handlerTags);
     ret->handlerBlocks.set(handlerBlocks);
     ret->sentTypes.set(sentTypes);
     ret->operands = std::move(operands);
     ret->cont = cont;
+    ret->type = contType.getContinuation().type.getSignature().results;
     ret->finalize();
     return ret;
   }

src/wasm/wasm-ir-builder.cpp

@@ -2675,7 +2675,8 @@ IRBuilder::makeResume(HeapType ct,
                           resumetable->targets,
                           resumetable->sentTypes,
                           std::move(curr.operands),
-                          curr.cont));
+                          curr.cont,
+                          ct));
 
   return Ok{};
 }
@@ -2715,7 +2716,8 @@ IRBuilder::makeResumeThrow(HeapType ct,
                                resumetable->targets,
                                resumetable->sentTypes,
                                std::move(curr.operands),
-                               curr.cont));
+                               curr.cont,
+                               ct));
   return Ok{};
 }
 

src/wasm/wasm-validator.cpp

@@ -4510,6 +4510,28 @@ void FunctionValidator::visitResumeThrow(ResumeThrow* curr) {
     return;
   }
 
+  if (curr->cont->type == Type::unreachable) {
+    return;
+  }
+
+  if (!shouldBeTrue(curr->cont->type.isRef(),
+                    curr,
+                    "resume_throw continuation must be a reference")) {
+    return;
+  }
+
+  auto type = curr->cont->type.getHeapType();
+  if (type.isMaybeShared(HeapType::nocont)) {
+    return;
+  }
+
+  if (!shouldBeTrue(
+        type.isContinuation(),
+        curr,
+        "resume_throw continuation must have a defined continuation type")) {
+    return;
+  }
+
   if (curr->tag) {
     // Normal resume_throw
     auto* tag = getModule()->getTagOrNull(curr->tag);
@@ -4551,28 +4573,6 @@ void FunctionValidator::visitResumeThrow(ResumeThrow* curr) {
     }
   }
 
-  if (curr->cont->type == Type::unreachable) {
-    return;
-  }
-
-  if (!shouldBeTrue(curr->cont->type.isRef(),
-                    curr,
-                    "resume_throw continuation must be a reference")) {
-    return;
-  }
-
-  auto type = curr->cont->type.getHeapType();
-  if (type.isMaybeShared(HeapType::nocont)) {
-    return;
-  }
-
-  if (!shouldBeTrue(
-        type.isContinuation(),
-        curr,
-        "resume_throw continuation must have a defined continuation type")) {
-    return;
-  }
-
   auto sig = type.getContinuation().type.getSignature();
 
   shouldBeEqualOrFirstIsUnreachable(