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[vm] Remove FallThroughError code in the VM

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Since Dart 2.0 we can never have FallThroughErrors.

The CFE does not synthesize breaks unterminated cases which never
reach the end of the block. For example:
* Call to something that returns never.
* Nested complete switch which returns from every branch.

In these cases we need to construct a correct control flow in the VM,
even though it is dead code. Because the CFE does not make the outer
switch a labelled statement, we cannot find a jump target in the VM.

Therefore, throw something (just not a FallThroughError). This should
never be hit at runtime, because it's dead code.

When the CFE emits synthetic breaks, we can remove this workaround.

TEST=build SDK and run default suites.

Bug: https://github.com/dart-lang/sdk/issues/50595
Change-Id: I595dd3baf7253b0ac4931445bd5b6da49e84cae4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/273740
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Tess Strickland <sstrickl@google.com>
This commit is contained in:
Daco Harkes 2022-12-08 11:51:31 +00:00 committed by Commit Queue
parent 636232628b
commit d86c043cbb
4 changed files with 9 additions and 38 deletions
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40
runtime/vm/compiler/frontend/kernel_binary_flowgraph.cc
View file

@ -4957,42 +4957,14 @@ Fragment StreamingFlowGraphBuilder::BuildSwitchCase(SwitchHelper* helper,
body_fragment += Drop();
}
// The Dart language specification mandates fall-throughs in [SwitchCase]es
// to be runtime errors.
// TODO(http://dartbug.com/50595): The CFE does not insert breaks for
// unterminated cases which never reach the end of their control flow.
// If the CFE inserts synthesized breaks, we can add an assert here instead.
if (!is_default && body_fragment.is_open() &&
(case_index < (helper->case_count() - 1))) {
const Class& klass = Class::ZoneHandle(
Z, Library::LookupCoreClass(Symbols::FallThroughError()));
ASSERT(!klass.IsNull());
const auto& error = klass.EnsureIsFinalized(thread());
ASSERT(error == Error::null());
GrowableHandlePtrArray<const String> pieces(Z, 3);
pieces.Add(Symbols::FallThroughError());
pieces.Add(Symbols::Dot());
pieces.Add(H.DartSymbolObfuscate("_create"));
const Function& constructor = Function::ZoneHandle(
Z, klass.LookupConstructorAllowPrivate(String::ZoneHandle(
Z, Symbols::FromConcatAll(H.thread(), pieces))));
ASSERT(!constructor.IsNull());
const String& url = H.DartSymbolPlain(
parsed_function()->function().ToLibNamePrefixedQualifiedCString());
// Create instance of _FallThroughError
body_fragment += AllocateObject(TokenPosition::kNoSource, klass, 0);
LocalVariable* instance = MakeTemporary();
// Call _FallThroughError._create constructor.
body_fragment += LoadLocal(instance); // this
body_fragment += Constant(url); // url
body_fragment += NullConstant(); // line
body_fragment +=
StaticCall(TokenPosition::kNoSource, constructor, 3, ICData::kStatic);
body_fragment += Drop();
// Throw the exception
const auto& error =
String::ZoneHandle(Z, Symbols::New(thread(), "Unreachable code."));
body_fragment += Constant(error);
body_fragment += ThrowException(TokenPosition::kNoSource);
body_fragment += Drop();
}

2
runtime/vm/compiler/frontend/kernel_to_il.cc
View file

@ -687,7 +687,7 @@ Fragment FlowGraphBuilder::ThrowTypeError() {
Fragment instructions;
// Create instance of _FallThroughError
// Create instance of _TypeError
instructions += AllocateObject(TokenPosition::kNoSource, klass, 0);
LocalVariable* instance = MakeTemporary();

4
runtime/vm/object_test.cc
View file

@ -7420,7 +7420,7 @@ static void CheckConcatAll(const String* data[], intptr_t n) {
ISOLATE_UNIT_TEST_CASE(Symbols_FromConcatAll) {
{
const String* data[3] = {&Symbols::FallThroughError(), &Symbols::Dot(),
const String* data[3] = {&Symbols::NullThrownError(), &Symbols::Dot(),
&Symbols::isPaused()};
CheckConcatAll(data, 3);
}
@ -7475,7 +7475,7 @@ ISOLATE_UNIT_TEST_CASE(Symbols_FromConcatAll) {
{
const String& empty = String::Handle(String::New(""));
const String* data[3] = {&Symbols::FallThroughError(), &empty,
const String* data[3] = {&Symbols::NullThrownError(), &empty,
&Symbols::isPaused()};
CheckConcatAll(data, 3);
}

1
runtime/vm/symbols.h
View file

@ -99,7 +99,6 @@ class ObjectPointerVisitor;
V(ExprTemp, ":expr_temp") \
V(ExternalOneByteString, "_ExternalOneByteString") \
V(ExternalTwoByteString, "_ExternalTwoByteString") \
V(FallThroughError, "FallThroughError") \
V(FfiAbiSpecificMapping, "_FfiAbiSpecificMapping") \
V(FfiBool, "Bool") \
V(FfiCallback, "_FfiCallback") \