[llvm] MC: Restructure MCFragment as a fixed part and a variable tail (PR #148544)

[Florian Mayer via llvm-commits]

fmayer wrote:

I think this made the UBSan bot unhappy (top frames in MC):

```
FAIL: Clang :: ASTMerge/codegen-body/test.c (842 of 91351)
******************** TEST 'Clang :: ASTMerge/codegen-body/test.c' FAILED ********************
Exit Code: 134
Command Output (stderr):
--
/home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/bin/clang -cc1 -internal-isystem /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/lib/clang/22/include -nostdsysteminc -emit-pch -o /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/test/ASTMerge/codegen-body/Output/test.c.tmp.1.ast /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/test/ASTMerge/codegen-body/Inputs/body1.c # RUN: at line 1
+ /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/bin/clang -cc1 -internal-isystem /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/lib/clang/22/include -nostdsysteminc -emit-pch -o /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/test/ASTMerge/codegen-body/Output/test.c.tmp.1.ast /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/test/ASTMerge/codegen-body/Inputs/body1.c
/home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/bin/clang -cc1 -internal-isystem /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/lib/clang/22/include -nostdsysteminc -emit-pch -o /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/test/ASTMerge/codegen-body/Output/test.c.tmp.2.ast /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/test/ASTMerge/codegen-body/Inputs/body2.c # RUN: at line 2
+ /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/bin/clang -cc1 -internal-isystem /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/lib/clang/22/include -nostdsysteminc -emit-pch -o /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/test/ASTMerge/codegen-body/Output/test.c.tmp.2.ast /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/test/ASTMerge/codegen-body/Inputs/body2.c
/home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/bin/clang -cc1 -internal-isystem /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/lib/clang/22/include -nostdsysteminc -emit-obj -o /dev/null -ast-merge /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/test/ASTMerge/codegen-body/Output/test.c.tmp.1.ast -ast-merge /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/test/ASTMerge/codegen-body/Output/test.c.tmp.2.ast /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/test/ASTMerge/codegen-body/test.c # RUN: at line 3
+ /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/bin/clang -cc1 -internal-isystem /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/lib/clang/22/include -nostdsysteminc -emit-obj -o /dev/null -ast-merge /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/test/ASTMerge/codegen-body/Output/test.c.tmp.1.ast -ast-merge /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/test/ASTMerge/codegen-body/Output/test.c.tmp.2.ast /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/test/ASTMerge/codegen-body/test.c
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.	Program arguments: /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/bin/clang -cc1 -internal-isystem /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/lib/clang/22/include -nostdsysteminc -emit-obj -o /dev/null -ast-merge /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/test/ASTMerge/codegen-body/Output/test.c.tmp.1.ast -ast-merge /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/test/ASTMerge/codegen-body/Output/test.c.tmp.2.ast /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/test/ASTMerge/codegen-body/test.c
1.	<eof> parser at end of file
2.	Code generation
 #0 0x00005663a9a036ee llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/Support/Unix/Signals.inc:834:13
 #1 0x00005663a9a0030f llvm::sys::RunSignalHandlers() /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/Support/Signals.cpp:105:18
 #2 0x00005663a9a049a8 SignalHandler(int, siginfo_t*, void*) /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/Support/Unix/Signals.inc:426:38
 #3 0x00007beaafe45250 (/lib/x86_64-linux-gnu/libc.so.6+0x45250)
 #4 0x00007beaafea3f1c pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0xa3f1c)
 #5 0x00007beaafe4519e raise (/lib/x86_64-linux-gnu/libc.so.6+0x4519e)
 #6 0x00007beaafe28902 abort (/lib/x86_64-linux-gnu/libc.so.6+0x28902)
 #7 0x00005663a5dcc45c (/home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/bin/clang+0xa72345c)
 #8 0x00005663a5dca2fe __sanitizer::Die() /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_termination.cpp:52:5
 #9 0x00005663a5de0099 (/home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/bin/clang+0xa737099)
#10 0x00005663a9606ad0 end /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/include/llvm/ADT/ArrayRef.h:352:42
#11 0x00005663a9606ad0 llvm::MCAssembler::layout() /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/MC/MCAssembler.cpp:0:0
#12 0x00005663a96075ee operator* /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/libcxx_install_ubsan/include/c++/v1/__memory/unique_ptr.h:268:13
#13 0x00005663a96075ee getWriter /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/include/llvm/MC/MCAssembler.h:179:46
#14 0x00005663a96075ee llvm::MCAssembler::Finish() /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/MC/MCAssembler.cpp:735:25
#15 0x00005663a96353c5 llvm::MCELFStreamer::finishImpl() /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/MC/MCELFStreamer.cpp:371:1
#16 0x00005663ab0827ac operator-> /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/libcxx_install_ubsan/include/c++/v1/__memory/unique_ptr.h:270:101
#17 0x00005663ab0827ac llvm::AsmPrinter::doFinalization(llvm::Module&) /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp:2778:3
#18 0x00005663a913f843 llvm::FPPassManager::doFinalization(llvm::Module&) /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:1462:13
#19 0x00005663a9135d7b runOnModule /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:1549:13
#20 0x00005663a9135d7b llvm::legacy::PassManagerImpl::run(llvm::Module&) /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:531:44
#21 0x00005663aa4c5881 RunCodegenPipeline /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/lib/CodeGen/BackendUtil.cpp:1261:9
#22 0x00005663aa4c5881 emitAssembly /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/lib/CodeGen/BackendUtil.cpp:1284:3
#23 0x00005663aa4c5881 clang::emitBackendOutput(clang::CompilerInstance&, clang::CodeGenOptions&, llvm::StringRef, llvm::Module*, clang::BackendAction, llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>, std::__1::unique_ptr<llvm::raw_pwrite_stream, std::__1::default_delete<llvm::raw_pwrite_stream>>, clang::BackendConsumer*) /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/lib/CodeGen/BackendUtil.cpp:1449:13
#24 0x00005663aa4dd2ec reset /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/libcxx_install_ubsan/include/c++/v1/__memory/unique_ptr.h:287:21
#25 0x00005663aa4dd2ec ~unique_ptr /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/libcxx_install_ubsan/include/c++/v1/__memory/unique_ptr.h:259:71
#26 0x00005663aa4dd2ec clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/lib/CodeGen/CodeGenAction.cpp:316:3
#27 0x00005663ac9f4c0b clang::ParseAST(clang::Sema&, bool, bool) /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/lib/Parse/ParseAST.cpp:0:13
#28 0x00005663aadf7555 operator bool /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/include/llvm/ADT/IntrusiveRefCntPtr.h:206:43
#29 0x00005663aadf7555 getDiagnostics /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/include/clang/Frontend/CompilerInstance.h:354:5
#30 0x00005663aadf7555 clang::ASTMergeAction::ExecuteAction() /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/lib/Frontend/ASTMerge.cpp:79:6
#31 0x00005663aac46514 clang::FrontendAction::Execute() /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/lib/Frontend/FrontendAction.cpp:1226:10
#32 0x00005663aab92710 getPtr /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/include/llvm/Support/Error.h:278:42
#33 0x00005663aab92710 operator bool /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/include/llvm/Support/Error.h:241:16
#34 0x00005663aab92710 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/lib/Frontend/CompilerInstance.cpp:1056:23
#35 0x00005663aadb05e3 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp:299:25
#36 0x00005663a5de9e46 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/tools/driver/cc1_main.cpp:297:15
#37 0x00005663a5de3c83 ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/tools/driver/driver.cpp:223:12
#38 0x00005663a5de2d85 clang_main(int, char**, llvm::ToolContext const&) /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/tools/driver/driver.cpp:264:12
#39 0x00005663a5dfb78b main /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/tools/driver/clang-driver.cpp:17:10
#40 0x00007beaafe2a3b8 (/lib/x86_64-linux-gnu/libc.so.6+0x2a3b8)
#41 0x00007beaafe2a47b __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a47b)
#42 0x00005663a5db47e5 _start (/home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/bin/clang+0xa70b7e5)
/home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/test/ASTMerge/codegen-body/Output/test.c.script: line 3: 2103241 Aborted                 (core dumped) /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/bin/clang -cc1 -internal-isystem /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/lib/clang/22/include -nostdsysteminc -emit-obj -o /dev/null -ast-merge /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/test/ASTMerge/codegen-body/Output/test.c.tmp.1.ast -ast-merge /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/test/ASTMerge/codegen-body/Output/test.c.tmp.2.ast /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/clang/test/ASTMerge/codegen-body/test.c
```

https://github.com/llvm/llvm-project/pull/148544