[Exceptions] Finish interpreter + optimizer support for try_table. (#…

…6814)

* Add interpreter support for exnref values.
* Fix optimization passes to support try_table.
* Enable the interpreter (but not in V8, see code) on exceptions.

scripts/fuzz_opt.py

@@ -352,10 +352,6 @@ def is_git_repo():
     'typed_continuations_contnew.wast',
     'typed_continuations_contbind.wast',
     'typed_continuations_suspend.wast',
-    # New EH implementation is in progress
-    'exception-handling.wast',
-    'translate-to-new-eh.wast',
-    'rse-eh.wast',
 ]
 
 
@@ -841,7 +837,9 @@ def can_run(self, wasm):
                 # V8 does not support shared memories when running with
                 # shared-everything enabled, so do not fuzz shared-everything
                 # for now.
-                return all_disallowed(['shared-everything'])
+                # Due to the V8 bug https://issues.chromium.org/issues/332931390
+                # we do not fuzz exception-handling either.
+                return all_disallowed(['shared-everything', 'exception-handling'])
 
             def can_compare_to_self(self):
                 # With nans, VM differences can confuse us, so only very simple VMs
@@ -1649,6 +1647,9 @@ def get_random_opts():
                 print('avoiding --flatten due to multivalue + reference types not supporting it (spilling of non-nullable tuples)')
                 print('TODO: Resolving https://github.com/WebAssembly/binaryen/issues/4824 may fix this')
                 continue
+            if '--enable-exception-handling' in FEATURE_OPTS:
+                print('avoiding --flatten due to exception-handling not supporting it (requires blocks with results)')
+                continue
             if '--gc' not in FEATURE_OPTS:
                 print('avoiding --flatten due to GC not supporting it (spilling of non-nullable locals)')
                 continue
@@ -1707,7 +1708,7 @@ def get_random_opts():
 # some features depend on other features, so if a required feature is
 # disabled, its dependent features need to be disabled as well.
 IMPLIED_FEATURE_OPTS = {
-    '--disable-reference-types': ['--disable-gc', '--disable-strings'],
+    '--disable-reference-types': ['--disable-gc', '--disable-exception-handling', '--disable-strings'],
     '--disable-gc': ['--disable-strings'],
 }
 

src/ir/ReFinalize.cpp

@@ -128,7 +128,12 @@ void ReFinalize::visitTableFill(TableFill* curr) { curr->finalize(); }
 void ReFinalize::visitTableCopy(TableCopy* curr) { curr->finalize(); }
 void ReFinalize::visitTableInit(TableInit* curr) { curr->finalize(); }
 void ReFinalize::visitTry(Try* curr) { curr->finalize(); }
-void ReFinalize::visitTryTable(TryTable* curr) { curr->finalize(); }
+void ReFinalize::visitTryTable(TryTable* curr) {
+  curr->finalize();
+  for (size_t i = 0; i < curr->catchDests.size(); i++) {
+    updateBreakValueType(curr->catchDests[i], curr->sentTypes[i]);
+  }
+}
 void ReFinalize::visitThrow(Throw* curr) { curr->finalize(); }
 void ReFinalize::visitRethrow(Rethrow* curr) { curr->finalize(); }
 void ReFinalize::visitThrowRef(ThrowRef* curr) { curr->finalize(); }

src/ir/effects.h

@@ -431,6 +431,14 @@ class EffectAnalyzer {
         self->pushTask(doStartTry, currp);
         return;
       }
+      if (auto* tryTable = curr->dynCast<TryTable>()) {
+        // We need to increment try depth before starting.
+        self->pushTask(doEndTryTable, currp);
+        self->pushTask(doVisitTryTable, currp);
+        self->pushTask(scan, &tryTable->body);
+        self->pushTask(doStartTryTable, currp);
+        return;
+      }
       PostWalker<InternalAnalyzer, OverriddenVisitor<InternalAnalyzer>>::scan(
         self, currp);
     }
@@ -472,6 +480,24 @@ class EffectAnalyzer {
       self->parent.catchDepth--;
     }
 
+    static void doStartTryTable(InternalAnalyzer* self, Expression** currp) {
+      auto* curr = (*currp)->cast<TryTable>();
+      // We only count 'try_table's with a 'catch_all' because instructions
+      // within a 'try_table' without a 'catch_all' can still throw outside of
+      // the try.
+      if (curr->hasCatchAll()) {
+        self->parent.tryDepth++;
+      }
+    }
+
+    static void doEndTryTable(InternalAnalyzer* self, Expression** currp) {
+      auto* curr = (*currp)->cast<TryTable>();
+      if (curr->hasCatchAll()) {
+        assert(self->parent.tryDepth > 0 && "try depth cannot be negative");
+        self->parent.tryDepth--;
+      }
+    }
+
     void visitBlock(Block* curr) {
       if (curr->name.is()) {
         parent.breakTargets.erase(curr->name); // these were internal breaks

src/ir/linear-execution.h

@@ -171,6 +171,12 @@ struct LinearExecutionWalker : public PostWalker<SubType, VisitorType> {
         self->pushTask(SubType::scan, &curr->cast<Try>()->body);
         break;
       }
+      case Expression::Id::TryTableId: {
+        self->pushTask(SubType::doVisitTryTable, currp);
+        self->pushTask(SubType::doNoteNonLinear, currp);
+        self->pushTask(SubType::scan, &curr->cast<TryTable>()->body);
+        break;
+      }
       case Expression::Id::ThrowId: {
         self->pushTask(SubType::doVisitThrow, currp);
         self->pushTask(SubType::doNoteNonLinear, currp);

src/ir/possible-contents.cpp

@@ -1135,8 +1135,38 @@ struct InfoCollector
     }
   }
   void visitTryTable(TryTable* curr) {
-    // TODO: optimize when possible
-    addRoot(curr);
+    receiveChildValue(curr->body, curr);
+
+    // Connect caught tags with their branch targets, and materialize non-null
+    // exnref values.
+    auto numTags = curr->catchTags.size();
+    for (Index tagIndex = 0; tagIndex < numTags; tagIndex++) {
+      auto tag = curr->catchTags[tagIndex];
+      auto target = curr->catchDests[tagIndex];
+
+      Index exnrefIndex = 0;
+      if (tag.is()) {
+        auto params = getModule()->getTag(tag)->sig.params;
+
+        for (Index i = 0; i < params.size(); i++) {
+          if (isRelevant(params[i])) {
+            info.links.push_back(
+              {TagLocation{tag, i},
+               BreakTargetLocation{getFunction(), target, i}});
+          }
+        }
+
+        exnrefIndex = params.size();
+      }
+
+      if (curr->catchRefs[tagIndex]) {
+        auto location = CaughtExnRefLocation{};
+        addRoot(location,
+                PossibleContents::fromType(Type(HeapType::exn, NonNullable)));
+        info.links.push_back(
+          {location, BreakTargetLocation{getFunction(), target, exnrefIndex}});
+      }
+    }
   }
   void visitThrow(Throw* curr) {
     auto& operands = curr->operands;

src/ir/possible-contents.h

@@ -473,6 +473,15 @@ struct TagLocation {
   }
 };
 
+// The location of an exnref materialized by a catch_ref or catch_all_ref clause
+// of a try_table. No data is stored here. exnrefs contain a tag and a payload
+// at run-time, as well as potential metadata such as stack traces, but we don't
+// track that. So this is the same as NullLocation in a way: we just need *a*
+// source of contents for places that receive an exnref.
+struct CaughtExnRefLocation {
+  bool operator==(const CaughtExnRefLocation& other) const { return true; }
+};
+
 // A null value. This is used as the location of the default value of a var in a
 // function, a null written to a struct field in struct.new_with_default, etc.
 struct NullLocation {
@@ -520,6 +529,7 @@ using Location = std::variant<ExpressionLocation,
                               SignatureResultLocation,
                               DataLocation,
                               TagLocation,
+                              CaughtExnRefLocation,
                               NullLocation,
                               ConeReadLocation>;
 
@@ -608,6 +618,12 @@ template<> struct hash<wasm::TagLocation> {
   }
 };
 
+template<> struct hash<wasm::CaughtExnRefLocation> {
+  size_t operator()(const wasm::CaughtExnRefLocation& loc) const {
+    return std::hash<const char*>()("caught-exnref-location");
+  }
+};
+
 template<> struct hash<wasm::NullLocation> {
   size_t operator()(const wasm::NullLocation& loc) const {
     return std::hash<wasm::Type>{}(loc.type);

src/literal.h

@@ -32,6 +32,7 @@ namespace wasm {
 
 class Literals;
 struct GCData;
+struct ExnData;
 
 class Literal {
   // store only integers, whose bits are deterministic. floats
@@ -44,6 +45,7 @@ class Literal {
     int64_t i64;
     uint8_t v128[16];
     // funcref function name. `isNull()` indicates a `null` value.
+    // TODO: handle cross-module calls using something other than a Name here.
     Name func;
     // A reference to GC data, either a Struct or an Array. For both of those we
     // store the referred data as a Literals object (which is natural for an
@@ -56,6 +58,8 @@ class Literal {
     // reference as its sole value even though internal i31 references do not
     // have a gcData.
     std::shared_ptr<GCData> gcData;
+    // A reference to Exn data.
+    std::shared_ptr<ExnData> exnData;
   };
 
 public:
@@ -85,6 +89,7 @@ class Literal {
     assert(type.isSignature());
   }
   explicit Literal(std::shared_ptr<GCData> gcData, HeapType type);
+  explicit Literal(std::shared_ptr<ExnData> exnData);
   explicit Literal(std::string_view string);
   Literal(const Literal& other);
   Literal& operator=(const Literal& other);
@@ -96,6 +101,7 @@ class Literal {
   // Whether this is GC data, that is, something stored on the heap (aside from
   // a null or i31). This includes structs, arrays, and also strings.
   bool isData() const { return type.isData(); }
+  bool isExn() const { return type.isExn(); }
   bool isString() const { return type.isString(); }
 
   bool isNull() const { return type.isNull(); }
@@ -303,6 +309,7 @@ class Literal {
     return func;
   }
   std::shared_ptr<GCData> getGCData() const;
+  std::shared_ptr<ExnData> getExnData() const;
 
   // careful!
   int32_t* geti32Ptr() {
@@ -742,6 +749,18 @@ struct GCData {
   GCData(HeapType type, Literals values) : type(type), values(values) {}
 };
 
+// The data of a (ref exn) literal.
+struct ExnData {
+  // The tag of this exn data.
+  // TODO: handle cross-module calls using something other than a Name here.
+  Name tag;
+
+  // The payload of this exn data.
+  Literals payload;
+
+  ExnData(Name tag, Literals payload) : tag(tag), payload(payload) {}
+};
+
 } // namespace wasm
 
 namespace std {

src/passes/CodeFolding.cpp

@@ -343,15 +343,18 @@ struct CodeFolding : public WalkerPass<ControlFlowWalker<CodeFolding>> {
         if (effects.danglingPop) {
           return false;
         }
-        // When an expression can throw and it is within a try scope, taking it
-        // out of the try scope changes the program's behavior, because the
-        // expression that would otherwise have been caught by the try now
-        // throws up to the next try scope or even up to the caller. We restrict
-        // the move if 'outOf' contains a 'try' anywhere in it. This is a
-        // conservative approximation because there can be cases that 'try' is
-        // within the expression that may throw so it is safe to take the
-        // expression out.
-        if (effects.throws() && !FindAll<Try>(outOf).list.empty()) {
+        // When an expression can throw and it is within a try/try_table scope,
+        // taking it out of the try/try_table scope changes the program's
+        // behavior, because the expression that would otherwise have been
+        // caught by the try/try_table now throws up to the next try/try_table
+        // scope or even up to the caller. We restrict the move if 'outOf'
+        // contains a 'try' or 'try_table' anywhere in it. This is a
+        // conservative approximation because there can be cases that
+        // 'try'/'try_table' is within the expression that may throw so it is
+        // safe to take the expression out.
+        // TODO: optimize this check to avoid two FindAlls.
+        if (effects.throws() &&
+            (FindAll<Try>(outOf).has() || FindAll<TryTable>(outOf).has())) {
           return false;
         }
       }

src/passes/DeadCodeElimination.cpp

@@ -185,6 +185,12 @@ struct DeadCodeElimination
           tryy->body->type == Type::unreachable && allCatchesUnreachable) {
         typeUpdater.changeType(tryy, Type::unreachable);
       }
+    } else if (auto* tryTable = curr->dynCast<TryTable>()) {
+      // try_table can finish normally only if its body finishes normally.
+      if (tryTable->type != Type::unreachable &&
+          tryTable->body->type == Type::unreachable) {
+        typeUpdater.changeType(tryTable, Type::unreachable);
+      }
     } else {
       WASM_UNREACHABLE("unimplemented DCE control flow structure");
     }

src/passes/SimplifyLocals.cpp

@@ -321,9 +321,9 @@ struct SimplifyLocals
            Expression** currp) {
     Expression* curr = *currp;
 
-    // Certain expressions cannot be sinked into 'try', and so at the start of
-    // 'try' we forget about them.
-    if (curr->is<Try>()) {
+    // Certain expressions cannot be sinked into 'try'/'try_table', and so at
+    // the start of 'try'/'try_table' we forget about them.
+    if (curr->is<Try>() || curr->is<TryTable>()) {
       std::vector<Index> invalidated;
       for (auto& [index, info] : self->sinkables) {
         // Expressions that may throw cannot be moved into a try (which might

src/passes/Vacuum.cpp

@@ -87,7 +87,7 @@ struct Vacuum : public WalkerPass<ExpressionStackWalker<Vacuum>> {
       // Some instructions have special handling in visit*, and we should do
       // nothing for them here.
       if (curr->is<Drop>() || curr->is<Block>() || curr->is<If>() ||
-          curr->is<Loop>() || curr->is<Try>()) {
+          curr->is<Loop>() || curr->is<Try>() || curr->is<TryTable>()) {
         return curr;
       }
       // Check if this expression itself has side effects, ignoring children.
@@ -435,6 +435,15 @@ struct Vacuum : public WalkerPass<ExpressionStackWalker<Vacuum>> {
     }
   }
 
+  void visitTryTable(TryTable* curr) {
+    // If try_table's body does not throw, the whole try_table can be replaced
+    // with the try_table's body.
+    if (!EffectAnalyzer(getPassOptions(), *getModule(), curr->body).throws()) {
+      replaceCurrent(curr->body);
+      return;
+    }
+  }
+
   void visitFunction(Function* curr) {
     auto* optimized =
       optimize(curr->body, curr->getResults() != Type::none, true);