emscripten-llvm/clang 10: Segmentation fault with -ffast-math when compiling GraphViz (lab.c)

Not sure if this is the correct place to report the bug or if it belongs at bugs.llvm.

I try to compile Viz.js (GraphViz for the web) and the compiler segfaults while compiling "lab.c" of GraphViz. I reduced the problem to:

lab.c (reduced to code that segfaults):
```c
#include

double XYZEpsilon = 216./24389.;
double XYZKappa = 24389./27.;

static double PivotXYZ(double n){
if (n > XYZEpsilon) return pow(n, 1/3.);
return (XYZKappa*n + 16)/116;
}

int main(int argc, char** argv) {
return PivotXYZ((double)argc);
}
```

Compile line: When I remove -ffast-math it works
```
emcc -ffast-math lab.c
```

```
> emcc --version
emcc (Emscripten gcc/clang-like replacement) 1.39.1 ((unknown revision))

> /usr/lib/emscripten-llvm/clang --version
clang version 10.0.0 (/srcdest/llvm-project 411f1885b655ea622fe124a87a6eadfd988d7a5e)
```

```
Stack dump:
0. Program arguments: /usr/lib/emscripten-llvm/clang-10 -cc1 -triple wasm32-unknown-emscripten -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name lab.c -mrelocation-model static -mthread-model posix -mframe-pointer=none -menable-no-infs -menable-no-nans -menable-unsafe-fp-math -fno-signed-zeros -mreassociate -freciprocal-math -fno-trapping-math -ffp-contract=fast -ffast-math -ffinite-math-only -masm-verbose -mconstructor-aliases -fuse-init-array -target-cpu generic -fvisibility hidden -dwarf-column-info -debugger-tuning=gdb -resource-dir /usr/lib/lib/clang/10.0.0 -D __EMSCRIPTEN_major__=1 -D __EMSCRIPTEN_minor__=39 -D __EMSCRIPTEN_tiny__=1 -D _LIBCPP_ABI_VERSION=2 -D unix -D __unix -D __unix__ -D EMSCRIPTEN -internal-isystem /usr/lib/lib/clang/10.0.0/include -internal-isystem /include/wasm32-emscripten -internal-isystem /include -Werror=implicit-function-declaration -fdebug-compilation-dir /tmp -ferror-limit 19 -fmessage-length 0 -fobjc-runtime=gnustep -fno-common -fdiagnostics-show-option -fcolor-diagnostics -nostdsysteminc -isystem/usr/lib/emscripten/system/include/libcxx -isystem/usr/lib/emscripten/system/lib/libcxxabi/include -isystem/usr/lib/emscripten/system/include/compat -isystem/usr/lib/emscripten/system/include -isystem/usr/lib/emscripten/system/include/libc -isystem/usr/lib/emscripten/system/lib/libc/musl/arch/emscripten -isystem/usr/lib/emscripten/system/local/include -isystem/usr/lib/emscripten/system/include/SDL -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr -o /tmp/emscripten_temp_ubun2igx/lab_0.o -x c lab.c
1. parser at end of file
2. Code generation
3. Running pass 'Function Pass Manager' on module 'lab.c'.
4. Running pass 'WebAssembly Assembly Printer' on function '@PivotXYZ'
#0 0x000055f415994bcb llvm::sys::PrintStackTrace(llvm::raw_ostream&) (/usr/lib/emscripten-llvm/clang-10+0x18b9bcb)
#1 0x000055f415992a64 llvm::sys::RunSignalHandlers() (/usr/lib/emscripten-llvm/clang-10+0x18b7a64)
#2 0x000055f415992bf6 (/usr/lib/emscripten-llvm/clang-10+0x18b7bf6)
#3 0x00007fbd2fcaa930 __restore_rt (/usr/lib/libpthread.so.0+0x14930)
#4 0x000055f414c61379 llvm::getLibcallSignature(llvm::WebAssemblySubtarget const&, char const*, llvm::SmallVectorImpl&, llvm::SmallVectorImpl&) (/usr/lib/emscripten-llvm/clang-10+0xb86379)
#5 0x000055f414c5dda8 (/usr/lib/emscripten-llvm/clang-10+0xb82da8)
#6 0x000055f414c5e14b (/usr/lib/emscripten-llvm/clang-10+0xb8314b)
#7 0x000055f414c57ed2 (/usr/lib/emscripten-llvm/clang-10+0xb7ced2)
#8 0x000055f41640f171 llvm::AsmPrinter::EmitFunctionBody() (/usr/lib/emscripten-llvm/clang-10+0x2334171)
#9 0x000055f414c5819d (/usr/lib/emscripten-llvm/clang-10+0xb7d19d)
#10 0x000055f415033116 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (/usr/lib/emscripten-llvm/clang-10+0xf58116)
#11 0x000055f4153b2360 llvm::FPPassManager::runOnFunction(llvm::Function&) (/usr/lib/emscripten-llvm/clang-10+0x12d7360)
#12 0x000055f4153b23b2 llvm::FPPassManager::runOnModule(llvm::Module&) (/usr/lib/emscripten-llvm/clang-10+0x12d73b2)
#13 0x000055f4153b1666 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/usr/lib/emscripten-llvm/clang-10+0x12d6666)
#14 0x000055f415bf56d2 clang::EmitBackendOutput(clang::DiagnosticsEngine&, clang::HeaderSearchOptions const&, clang::CodeGenOptions const&, clang::TargetOptions const&, clang::LangOptions const&, llvm::DataLayout const&, llvm::Module*, clang::BackendAction, std::unique_ptr >) (/usr/lib/emscripten-llvm/clang-10+0x1b1a6d2)
#15 0x000055f41676fd92 (/usr/lib/emscripten-llvm/clang-10+0x2694d92)
#16 0x000055f4174bc0a9 clang::ParseAST(clang::Sema&, bool, bool) (/usr/lib/emscripten-llvm/clang-10+0x33e10a9)
#17 0x000055f41676d663 clang::CodeGenAction::ExecuteAction() (/usr/lib/emscripten-llvm/clang-10+0x2692663)
#18 0x000055f416167849 clang::FrontendAction::Execute() (/usr/lib/emscripten-llvm/clang-10+0x208c849)
#19 0x000055f41612294e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/usr/lib/emscripten-llvm/clang-10+0x204794e)
#20 0x000055f41623c1cd clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/usr/lib/emscripten-llvm/clang-10+0x21611cd)
#21 0x000055f4149c7cab cc1_main(llvm::ArrayRef, char const*, void*) (/usr/lib/emscripten-llvm/clang-10+0x8eccab)
#22 0x000055f414968561 main (/usr/lib/emscripten-llvm/clang-10+0x88d561)
#23 0x00007fbd2f51f153 __libc_start_main (/usr/lib/libc.so.6+0x27153)
#24 0x000055f4149c5afe _start (/usr/lib/emscripten-llvm/clang-10+0x8eaafe)
clang-10: error: unable to execute command: Segmentation fault (core dumped)
clang-10: error: clang frontend command failed due to signal (use -v to see invocation)
clang version 10.0.0 (/srcdest/llvm-project 411f1885b655ea622fe124a87a6eadfd988d7a5e)
Target: wasm32-unknown-emscripten
```

Riproduci il problema con la lab.c ridotta e emcc -ffast-math, quindi ispeziona il percorso di WebAssembly Assembly Printer indicato nello stack dump, incluso getLibcallSignature. Il lavoro è completato quando il caso ridotto viene compilato senza un Segmentation Fault con -ffast-math, mentre il confronto senza flag continua ad avere successo.

Scritto dal modello di indicizzazione a partire dal testo della issue.