gcc warning in JavaScriptCore/wtf

[Alp Toker]

This compiler warning is issued by gcc 4.1.2 (which is apparently more recent than what's used by Apple). It was noticed when building the "gdk" port.

bdash points out that "according to the man page, the warning will only be emitted in unsafe cases. there's a separate flag to turn on warning in all cases, even those which are potentially safe"

So it's possible that gcc is now good enough to identify more "unsafe" conditions, in which case the bug should be fixed, or it might be a regression in gcc's detection of unsafe conditions, in which case it might be worth considering suppressing the warning. I leave it to someone familiar with the code to determine this.

I include the flags we use in the gdk port for reference.


g++ -c -o obj-gnu/webcore_gdk_RenderApplet.o -I../../../JavaScriptCore -I../.. -I../../bindings/js -I../../bridge -I../../css -I../../DerivedSources/WebCore -I../../dom -I../../editing -I../../ForwardingHeaders/kjs -I../../history -I../../html -I../../include -I../../loader -I../../loader/gdk -I../../loader/icon -I../../page -I../../platform -I../../platform/graphics -I../../platform/graphics/gdk -I../../platform/image-decoders -I../../platform/image-decoders/bmp -I../../platform/image-decoders/gif -I../../platform/image-decoders/ico -I../../platform/image-decoders/jpeg -I../../platform/image-decoders/png -I../../platform/image-decoders/xbm -I../../platform/image-decoders/zlib -I../../platform/network -I../../platform/network/gdk -I../../rendering -I../../xml -DENABLE_XSLT=1 -DLINUX -DUSE_CONSERVATIVE_GC=0 -DHAVE_FUNC_ISNAN -D_THREAD_SAFE -pthread -g -I../../platform/gdk -I../../platform/network/gdk -DBUILDING_GDK__ -DBUILDING_CAIRO__ -Iplatform/gdk -Iplatform/graphics/cairo -DENABLE_XPATH -I/usr/include/libxml2 -I/usr/include/libxml2 -g -Wall -O2  -I/usr/include/freetype2    -I/usr/include/gtk-2.0 -I/usr/lib/gtk-2.0/include -I/usr/include/atk-1.0 -I/usr/include/cairo -I/usr/include/pango-1.0 -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/freetype2 -I/usr/include/libpng12    -I/usr/include/cairo -I/usr/include/freetype2 -I/usr/include/libpng12    -fPIC -DPIC -fno-rtti -fno-exceptions   -MTobj-gnu/webcore_gdk_RenderApplet.o -MF`echo obj-gnu/webcore_gdk_RenderApplet.o | sed -e 's,\.o$,.d,'` -MD ../../rendering/RenderApplet.cpp
../../../JavaScriptCore/wtf/HashTable.h: In static member function 'static void WTF::RefCounter<WTF::PairBaseHashTraits<FirstTraits, SecondTraits>, ValueStorageTraits>::deref(const typename ValueStorageTraits::TraitType&) [with FirstTraits = WTF::HashTraits<WebCore::String>, SecondTraits = WTF::HashTraits<WebCore::String>, ValueStorageTraits = WTF::PairHashTraits<WTF::HashTraits<WebCore::StringImpl*>, WTF::HashTraits<int> >]':
../../../JavaScriptCore/wtf/HashMap.h:291:   instantiated from 'void WTF::HashMap<KeyArg, MappedArg, HashArg, KeyTraitsArg, MappedTraitsArg>::remove(WTF::HashTableIteratorAdapter<WTF::HashTable<typename WTF::HashKeyStorageTraits<HashArg, KeyTraitsArg>::Traits::TraitType, typename WTF::PairHashTraits<typename WTF::HashKeyStorageTraits<HashArg, KeyTraitsArg>::Traits, typename MappedTraitsArg::StorageTraits>::TraitType, WTF::PairFirstExtractor<typename WTF::PairHashTraits<typename WTF::HashKeyStorageTraits<HashArg, KeyTraitsArg>::Traits, typename MappedTraitsArg::StorageTraits>::TraitType>, typename WTF::HashKeyStorageTraits<HashArg, KeyTraitsArg>::Hash, WTF::PairHashTraits<typename WTF::HashKeyStorageTraits<HashArg, KeyTraitsArg>::Traits, typename MappedTraitsArg::StorageTraits>, typename WTF::HashKeyStorageTraits<HashArg, KeyTraitsArg>::Traits>, typename WTF::PairBaseHashTraits<KeyTraitsArg, MappedTraitsArg>::TraitType>) [with KeyArg = WebCore::String, MappedArg = WebCore::String, HashArg = WTF::CaseInsensitiveHash<WebCore::String>, KeyTraitsArg = WTF::HashTraits<WebCore::String>, MappedTraitsArg = WTF::HashTraits<WebCore::String>]'
../../../JavaScriptCore/wtf/HashMap.h:298:   instantiated from 'void WTF::HashMap<KeyArg, MappedArg, HashArg, KeyTraitsArg, MappedTraitsArg>::remove(const typename KeyTraitsArg::TraitType&) [with KeyArg = WebCore::String, MappedArg = WebCore::String, HashArg = WTF::CaseInsensitiveHash<WebCore::String>, KeyTraitsArg = WTF::HashTraits<WebCore::String>, MappedTraitsArg = WTF::HashTraits<WebCore::String>]'
../../platform/network/ResourceRequest.h:132:   instantiated from here
../../../JavaScriptCore/wtf/HashTable.h:895: warning: dereferencing type-punned pointer will break strict-aliasing rules
../../../JavaScriptCore/wtf/HashMap.h: In static member function 'static void WTF::HashMapTranslator<false, ValueType, ValueStorageTraits, HashFunctions>::translate(typename ValueStorageTraits::TraitType&, const typename ValueType::first_type&, const typename ValueType::second_type&, unsigned int) [with ValueType = std::pair<WebCore::String, WebCore::String>, ValueStorageTraits = WTF::PairHashTraits<WTF::HashTraits<WebCore::StringImpl*>, WTF::HashTraits<int> >, HashFunctions = WTF::StrHash<WebCore::String>]':
../../../JavaScriptCore/wtf/HashTable.h:443:   instantiated from 'std::pair<typename WTF::HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits>::iterator, bool> WTF::HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits>::add(const T&, const Extra&) [with T = WebCore::String, Extra = WebCore::String, HashTranslator = WTF::HashMapTranslator<false, std::pair<WebCore::String, WebCore::String>, WTF::PairHashTraits<WTF::HashTraits<WebCore::StringImpl*>, WTF::HashTraits<int> >, WTF::StrHash<WebCore::String> >, Key = WebCore::StringImpl*, Value = std::pair<WebCore::StringImpl*, int>, Extractor = WTF::PairFirstExtractor<std::pair<WebCore::StringImpl*, int> >, HashFunctions = WTF::StrHash<WebCore::StringImpl*>, Traits = WTF::PairHashTraits<WTF::HashTraits<WebCore::StringImpl*>, WTF::HashTraits<int> >, KeyTraits = WTF::HashTraits<WebCore::StringImpl*>]'
../../../JavaScriptCore/wtf/HashMap.h:255:   instantiated from 'std::pair<typename WTF::HashMap<KeyArg, MappedArg, HashArg, KeyTraitsArg, MappedTraitsArg>::iterator, bool> WTF::HashMap<KeyArg, MappedArg, HashArg, KeyTraitsArg, MappedTraitsArg>::inlineAdd(const typename KeyTraitsArg::TraitType&, const typename MappedTraitsArg::TraitType&) [with KeyArg = WebCore::String, MappedArg = WebCore::String, HashArg = WTF::StrHash<WebCore::String>, KeyTraitsArg = WTF::HashTraits<WebCore::String>, MappedTraitsArg = WTF::HashTraits<WebCore::String>]'
../../../JavaScriptCore/wtf/HashMap.h:262:   instantiated from 'std::pair<typename WTF::HashMap<KeyArg, MappedArg, HashArg, KeyTraitsArg, MappedTraitsArg>::iterator, bool> WTF::HashMap<KeyArg, MappedArg, HashArg, KeyTraitsArg, MappedTraitsArg>::set(const typename KeyTraitsArg::TraitType&, const typename MappedTraitsArg::TraitType&) [with KeyArg = WebCore::String, MappedArg = WebCore::String, HashArg = WTF::StrHash<WebCore::String>, KeyTraitsArg = WTF::HashTraits<WebCore::String>, MappedTraitsArg = WTF::HashTraits<WebCore::String>]'
../../rendering/RenderApplet.cpp:86:   instantiated from here
../../../JavaScriptCore/wtf/HashMap.h:147: warning: dereferencing type-punned pointer will break strict-aliasing rules
../../../JavaScriptCore/wtf/HashTable.h: In static member function 'static void WTF::RefCounter<WTF::PairBaseHashTraits<FirstTraits, SecondTraits>, ValueStorageTraits>::ref(const typename ValueStorageTraits::TraitType&) [with FirstTraits = WTF::HashTraits<WebCore::String>, SecondTraits = WTF::HashTraits<WebCore::String>, ValueStorageTraits = WTF::PairHashTraits<WTF::HashTraits<WebCore::StringImpl*>, WTF::HashTraits<int> >]':
../../../JavaScriptCore/wtf/HashTable.h:922:   instantiated from 'static void WTF::HashTableRefCounterBase<true, HashTableType, ValueTraits>::refAll(HashTableType&) [with HashTableType = WTF::HashTable<WebCore::StringImpl*, std::pair<WebCore::StringImpl*, int>, WTF::PairFirstExtractor<std::pair<WebCore::StringImpl*, int> >, WTF::StrHash<WebCore::StringImpl*>, WTF::PairHashTraits<WTF::HashTraits<WebCore::StringImpl*>, WTF::HashTraits<int> >, WTF::HashTraits<WebCore::StringImpl*> >, ValueTraits = WTF::PairBaseHashTraits<WTF::HashTraits<WebCore::String>, WTF::HashTraits<WebCore::String> >]'
../../../JavaScriptCore/wtf/HashTable.h:936:   instantiated from 'static void WTF::HashTableRefCounter<HashTableType, ValueTraits>::refAll(HashTableType&) [with HashTableType = WTF::HashTable<WebCore::StringImpl*, std::pair<WebCore::StringImpl*, int>, WTF::PairFirstExtractor<std::pair<WebCore::StringImpl*, int> >, WTF::StrHash<WebCore::StringImpl*>, WTF::PairHashTraits<WTF::HashTraits<WebCore::StringImpl*>, WTF::HashTraits<int> >, WTF::HashTraits<WebCore::StringImpl*> >, ValueTraits = WTF::PairBaseHashTraits<WTF::HashTraits<WebCore::String>, WTF::HashTraits<WebCore::String> >]'
../../../JavaScriptCore/wtf/HashMap.h:154:   instantiated from 'void WTF::HashMap<KeyArg, MappedArg, HashArg, KeyTraitsArg, MappedTraitsArg>::refAll() [with KeyArg = WebCore::String, MappedArg = WebCore::String, HashArg = WTF::StrHash<WebCore::String>, KeyTraitsArg = WTF::HashTraits<WebCore::String>, MappedTraitsArg = WTF::HashTraits<WebCore::String>]'
../../../JavaScriptCore/wtf/HashMap.h:172:   instantiated from 'WTF::HashMap<KeyArg, MappedArg, HashArg, KeyTraitsArg, MappedTraitsArg>::HashMap(const WTF::HashMap<KeyArg, MappedArg, HashArg, KeyTraitsArg, MappedTraitsArg>&) [with KeyArg = WebCore::String, MappedArg = WebCore::String, HashArg = WTF::StrHash<WebCore::String>, KeyTraitsArg = WTF::HashTraits<WebCore::String>, MappedTraitsArg = WTF::HashTraits<WebCore::String>]'
../../rendering/RenderApplet.cpp:41:   instantiated from here
../../../JavaScriptCore/wtf/HashTable.h:891: warning: dereferencing type-punned pointer will break strict-aliasing rules

[Mark Rowe (bdash)]

CC'ing Maciej on this bug as the warnings are from the HashTable/HashMap code in WTF and he was the original author of that code.

[Cameron Zwarich (cpst)]

Isn't this now fixed?

[Alexey Proskuryakov]

This was fixed back in April as <rdar://problem/5657459>.