Help with working around an ICE in Apple clang


some code of mine triggers an ICE with Apple clang version 3.1 (tags/Apple/clang-318.0.61) but not with the released clang 3.1. Unfortunately, I need to support the version coming with Xcode. I was hoping the experts on this mailing list could help me make sense of the problem and point me toward coming with a workaround better than the only solution I could find by myself (see below).

Here is how to reproduce the problem. With the file attached to this message,

~> /usr/bin/c++ -S -O3 -I$cctbxsrc -I$cctbx_build_default/include -I$cctbxroot/boost finalise_at_last.cpp

0 clang 0x00000001101dd422 _ZL15PrintStackTracePv + 34
1 clang 0x00000001101dd8a9 _ZL13SignalHandleri + 553
2 libsystem_c.dylib 0x00007fff8d311cfa _sigtramp + 26
3 libsystem_c.dylib 0x00000001109560a8 _sigtramp + 18446603342720549832
4 clang 0x000000010f55d7c4 llvm::SelectionDAGBuilder::visitRet(llvm::ReturnInst const&) + 1428
5 clang 0x000000010f55cd60 llvm::SelectionDAGBuilder::visit(unsigned int, llvm::User const&) + 48
6 clang 0x000000010f55c592 llvm::SelectionDAGBuilder::visit(llvm::Instruction const&) + 66
7 clang 0x000000010f55c4c8 llvm::SelectionDAGISel::SelectBasicBlock(llvm::ilist_iterator<llvm::Instruction const>, llvm::ilist_iterator<llvm::Instruction const>, bool&) + 40
8 clang 0x000000010f489f91 llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) + 2417
9 clang 0x000000010f4851d5 llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) + 789
10 clang 0x000000010f484eae llvm::MachineFunctionPass::runOnFunction(llvm::Function&) + 110
11 clang 0x000000010f479fb2 llvm::FPPassManager::runOnFunction(llvm::Function&) + 322
12 clang 0x000000010f47f4bb llvm::FPPassManager::runOnModule(llvm::Module&) + 155
13 clang 0x000000010f47a8c1 llvm::MPPassManager::runOnModule(llvm::Module&) + 289
14 clang 0x000000010f47a2c5 llvm::PassManagerImpl::run(llvm::Module&) + 277
15 clang 0x000000010f47a1ad llvm::PassManager::run(llvm::Module&) + 13
16 clang 0x000000010f458e3c clang::EmitBackendOutput(clang::DiagnosticsEngine&, clang::CodeGenOptions const&, clang::TargetOptions const&, clang::LangOptions const&, llvm::Module*, clang::BackendAction, llvm::raw_ostream*) + 4508
17 clang 0x000000010f456641 clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) + 513
18 clang 0x000000010f3220f6 clang::ParseAST(clang::Sema&, bool) + 406
19 clang 0x000000010f320bd7 clang::CodeGenAction::ExecuteAction() + 855
20 clang 0x000000010f2f313f clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) + 879
21 clang 0x000000010f2f1dcb clang::ExecuteCompilerInvocation(clang::CompilerInstance*) + 2683
22 clang 0x000000010f2e45ce cc1_main(char const**, char const**, char const*, void*) + 5086
23 clang 0x000000010f2bedd8 main + 648
24 clang 0x000000010f2beb44 start + 52
Stack dump:
0. Program arguments: /usr/bin/clang -cc1 -triple x86_64-apple-macosx10.7.4 -S -disable-free -disable-llvm-verifier -main-file-name finalise_at_last.cpp -pic-level 2 -mdisable-fp-elim -relaxed-aliasing -masm-verbose -munwind-tables -target-cpu core2 -target-linker-version 128.2 -coverage-file finalise_at_last.s -resource-dir /usr/bin/../lib/clang/3.1 -I /Users/luc/Developer/cctbx/cctbx_project -I /Users/luc/Developer/cctbx/cctbx_build_default/include -I /Users/luc/Developer/cctbx/boost -fmodule-cache-path /var/folders/kx/qz2frq7d0p9fn8rg0w4gmmjm0000gn/T/clang-module-cache -O3 -fdeprecated-macro -fdebug-compilation-dir /Users/luc/Developer/Tests/clang-Xcode-4-4-symm-rank-1-crash -ferror-limit 19 -fmessage-length 104 -stack-protector 1 -fblocks -fobjc-runtime-has-arc -fobjc-runtime-has-weak -fobjc-dispatch-method=mixed -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -o finalise_at_last.s -x c++ finalise_at_last.cpp
1. <eof> parser at end of file
2. Code generation
3. Running pass 'Function Pass Manager' on module 'finalise_at_last.cpp'.
4. Running pass 'X86 DAG->DAG Instruction Selection' on function '@_Z16finalise_at_lastmPdS_'

Thanks in advance for any help,

Luc Bourhis

finalise_at_last.cpp (1.24 KB)

which is replacing -O3 by -O2

Your version of clang is from Xcode 4.3. 4.4 is out already, you should try to update Xcode to the latest version.

This isn't really the right place to discuss Xcode though, a better place would be the Apple Developer Forums ( or their bugtracker.

- Ben

Looks like it's optimizer crash. Could you reduce your optimization level to -O2 or -O0, at least for subject source file?

Hmm, probably it's the best workaround for this issue.

The problem is that the actual code is a member function of a class template another member function of which contains a hotspot, i.e. -O3 is important here. And because of the use of template, I can't easily compile one bit with -O2 and another one with -O3.
Basically, my hope was that I could tweak the code so as to spoil the optimisation that crashes. But for that I would need to understand the optimisation...

Luc Bourhis