[llvm] r317579 - Reland "Correct dwarf unwind information in function epilogue for X86"

Wed Nov 8 13:21:15 PST 2017

There is a design issue with making CFI_INSTRUCTION duplicable. Darwin
compact unwind info emission can't handle multiple prologue setups. I will
revert this and put the reduced test case in the commit message.

On Wed, Nov 8, 2017 at 10:43 AM, Reid Kleckner <rnk at google.com> wrote:

> I confirmed this caused a regression for AArch64 and I am reducing a test
> case.
>
>
> On Wed, Nov 8, 2017 at 9:34 AM, Reid Kleckner <rnk at google.com> wrote:
>
>> I suspect this change introduced a bug in compact unwind info on AArch64:
>> https://logs.chromium.org/v/?s=chromium%2Fbb%2Fchromium.clan
>> g%2FToTiOS%2F250%2F%2B%2Frecipes%2Fsteps%2Fcompile%2F0%2Fstdout
>>
>> FAILED: ios_clang_arm64/obj/third_party/opus/opus/pitch.o
>> ...
>> Assertion failed: (StackSize == 0 && "We already have the CFA offset!"),
>> function generateCompactUnwindEncoding, file /b/c/b/ToTiOS/src/third_party/
>> llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp, line 487.
>> 0  clang                    0x00000001035d7fb8
>> llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 40
>> 1  clang                    0x00000001035d86b6
>> llvm::sys::PrintStackTraceOnErrorSignal(llvm::StringRef, bool) + 838
>> 2  libsystem_platform.dylib 0x00007fffeb995bba _sigtramp + 26
>> 3  clang                    0x0000000103294e79
>> llvm::MCCVLineEntry::Make(llvm::MCObjectStreamer*) + 25
>> 4  libsystem_c.dylib        0x00007fffeb81c420 abort + 129
>> 5  libsystem_c.dylib        0x00007fffeb7e3893 basename_r + 0
>> 6  clang                    0x0000000101e22067
>> llvm::createAArch64beAsmBackend(llvm::Target const&,
>> llvm::MCRegisterInfo const&, llvm::Triple const&, llvm::StringRef,
>> llvm::MCTargetOptions const&) + 8631
>> 7  clang                    0x00000001032bf4ef
>> llvm::MCStreamer::generateCompactUnwindEncodings(llvm::MCAsmBackend*) +
>> 79
>> 8  clang                    0x00000001032a1196
>> llvm::MCDwarfFrameEmitter::Emit(llvm::MCObjectStreamer&,
>> llvm::MCAsmBackend*, bool) + 38
>> 9  clang                    0x00000001032b806e
>> llvm::MCObjectStreamer::EmitFrames(llvm::MCAsmBackend*) + 62
>> 10 clang                    0x00000001032b12f5
>> llvm::createMachOStreamer(llvm::MCContext&,
>> std::__1::unique_ptr<llvm::MCAsmBackend, std::__1::default_delete<llvm::MCAsmBackend>
>> >&&, llvm::raw_pwrite_stream&, std::__1::unique_ptr<llvm::MCCodeEmitter,
>> std::__1::default_delete<llvm::MCCodeEmitter> >&&, bool, bool, bool) +
>> 5749
>> 11 clang                    0x00000001032c37f2 llvm::MCStreamer::Finish()
>> + 306
>> 12 clang                    0x0000000103d6e271
>> llvm::AsmPrinter::doFinalization(llvm::Module&) + 3489
>> 13 clang                    0x0000000102ffa740
>> llvm::FPPassManager::doFinalization(llvm::Module&) + 80
>> 14 clang                    0x0000000102ffac8d
>> llvm::legacy::PassManagerImpl::run(llvm::Module&) + 1277
>> 15 clang                    0x000000010380cd33
>> clang::EmitBackendOutput(clang::DiagnosticsEngine&,
>> clang::HeaderSearchOptions const&, clang::CodeGenOptions const&,
>> clang::TargetOptions const&, clang::LangOptions const&, llvm::DataLayout
>> const&, llvm::Module*, clang::BackendAction, std::__1::unique_ptr<llvm::raw_pwrite_stream,
>> std::__1::default_delete<llvm::raw_pwrite_stream> >) + 15571
>> 16 clang                    0x0000000103a44ed5
>> clang::EmitObjAction::EmitObjAction(llvm::LLVMContext*) + 2341
>> 17 clang                    0x0000000103d10ccc
>> clang::MultiplexConsumer::HandleTranslationUnit(clang::ASTContext&) + 44
>> 18 clang                    0x00000001044cdfb5
>> clang::ParseAST(clang::Sema&, bool, bool) + 469
>> 19 clang                    0x0000000103ccdfdc
>> clang::FrontendAction::Execute() + 76
>> 20 clang                    0x0000000103c86e41
>> clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) + 1217
>> 21 clang                    0x0000000103d340fa
>> clang::ExecuteCompilerInvocation(clang::CompilerInstance*) + 4970
>> 22 clang                    0x0000000101c86a57
>> cc1_main(llvm::ArrayRef<char const*>, char const*, void*) + 1399
>> 23 clang                    0x0000000101c850df main + 11951
>> 24 libdyld.dylib            0x00007fffeb788255 start + 1
>>
>> I'll try to get a reproducer.
>>
>> On Tue, Nov 7, 2017 at 6:40 AM, Petar Jovanovic via llvm-commits <
>> llvm-commits at lists.llvm.org> wrote:
>>
>>> Author: petarj
>>> Date: Tue Nov  7 06:40:27 2017
>>> New Revision: 317579
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=317579&view=rev
>>> Log:
>>> Reland "Correct dwarf unwind information in function epilogue for X86"
>>>
>>> Reland r317100 with minor fix regarding ComputeCommonTailLength function
>>> in
>>> BranchFolding.cpp. Skipping top CFI instructions block needs to executed
>>> on
>>> several more return points in ComputeCommonTailLength().
>>>
>>> Original r317100 message:
>>>
>>> "Correct dwarf unwind information in function epilogue for X86"
>>>
>>> This patch aims to provide correct dwarf unwind information in function
>>> epilogue for X86.
>>>
>>> It consists of two parts. The first part inserts CFI instructions that
>>> set
>>> appropriate cfa offset and cfa register in emitEpilogue() in
>>> X86FrameLowering. This part is X86 specific.
>>>
>>> The second part is platform independent and ensures that:
>>>
>>> - CFI instructions do not affect code generation
>>> - Unwind information remains correct when a function is modified by
>>>   different passes. This is done in a late pass by analyzing information
>>>   about cfa offset and cfa register in BBs and inserting additional CFI
>>>   directives where necessary.
>>>
>>> Changed CFI instructions so that they:
>>>
>>> - are duplicable
>>> - are not counted as instructions when tail duplicating or tail merging
>>> - can be compared as equal
>>>
>>> Added CFIInstrInserter pass:
>>>
>>> - analyzes each basic block to determine cfa offset and register valid at
>>>   its entry and exit
>>> - verifies that outgoing cfa offset and register of predecessor blocks
>>> match
>>>   incoming values of their successors
>>> - inserts additional CFI directives at basic block beginning to correct
>>> the
>>>   rule for calculating CFA
>>>
>>> Having CFI instructions in function epilogue can cause incorrect CFA
>>> calculation rule for some basic blocks. This can happen if, due to basic
>>> block reordering, or the existence of multiple epilogue blocks, some of
>>> the
>>> blocks have wrong cfa offset and register values set by the epilogue
>>> block
>>> above them.
>>>
>>> CFIInstrInserter is currently run only on X86, but can be used by any
>>> target
>>> that implements support for adding CFI instructions in epilogue.
>>>
>>>
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