<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/109929>109929</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [ARM] musttail attribute fails with LTO and mismatched -ffast-math options
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            backend:ARM,
            crash-on-valid
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          ostannard
      </td>
    </tr>
</table>

<pre>
    This code causes an error in the ARM backend when built with LTO, and one part is build with -ffast-math, and the other with UBSan:
```c
struct function_pointers {
  double (*F95)(void);
};

void init_0(struct function_pointers *p);

double F93(void);

#ifdef PART1
struct function_pointers actual_fptrs;

[[clang::noinline]] double F90(void) {
  [[clang::musttail]] return F93();
}

double F95(void) { return 0.0; }

signed int main(void) {
  actual_fptrs.F95 = &F95;
  init_0(&actual_fptrs);
  F90();

  return 0;
}
#endif

#ifdef PART2
static struct function_pointers *fptrs;

void init_0(struct function_pointers *p) { fptrs = p; }

double F93(void) {
  [[clang::musttail]] return fptrs->F95();
}
#endif
```

```sh
#!/bin/bash -xe

/work/llvm/install/bin/clang --target=arm-none-eabi -march=armv7-a -c test.c -o part1.bc -O1 -flto -DPART1 -ffast-math
/work/llvm/install/bin/clang --target=arm-none-eabi -march=armv7-a -c test.c -o part2.bc -O1 -flto -DPART2 -fsanitize=undefined -fsanitize-trap=undefined
/work/llvm/install/bin/llvm-lto2 run part1.bc part2.bc -o test.o \
  -r part1.bc,F90,pl \
  -r part1.bc,F93,l \
  -r part1.bc,F95,pl \
  -r part1.bc,main,px \
  -r part1.bc,init_0,l \
  -r part1.bc,actual_fptrs,pl \
  -r part2.bc,init_0,pl \
  -r part2.bc,F93,pl
```

```
$ ./run.sh 
+ /work/llvm/install/bin/clang --target=arm-none-eabi -march=armv7-a -c test.c -o part1.bc -O1 -flto -DPART1 -ffast-math
+ /work/llvm/install/bin/clang --target=arm-none-eabi -march=armv7-a -c test.c -o part2.bc -O1 -flto -DPART2 -fsanitize=undefined -fsanitize-trap=undefined
+ /work/llvm/install/bin/llvm-lto2 run part1.bc part2.bc -o test.o -r part1.bc,F90,pl -r part1.bc,F93,l -r part1.bc,F95,pl -r part1.bc,main,px -r part1.bc,init_0,l -r part1.bc,actual_fptrs,pl -r part2.bc,init_0,pl -r part2.bc,F93,pl
LLVM ERROR: failed to perform tail call elimination on a call site marked musttail
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.      Program arguments: /work/llvm/install/bin/llvm-lto2 /work/llvm/install/bin/llvm-lto2 part1.bc part2.bc -o test.o -r part1.bc,F90,pl -r part1.bc,F93,l -r part1.bc,F95,pl -r part1.bc,main,px -r part1.bc,init_0,l -r part1.bc,actual_fptrs,pl -r part2.bc,init_0,pl -r part2.bc,F93,pl
1.      Running pass 'Function Pass Manager' on module 'ld-temp.o'.
2.      Running pass 'ARM Instruction Selection' on function '@F90'
 #0 0x00005566b41c38a7 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/work/llvm/install/bin/llvm-lto2+0x64158a7)
 #1 0x00005566b41c148e llvm::sys::RunSignalHandlers() (/work/llvm/install/bin/llvm-lto2+0x641348e)
 #2 0x00005566b41c3f7a SignalHandler(int) Signals.cpp:0:0
 #3 0x00007f1223242520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x00007f12232969fc __pthread_kill_implementation ./nptl/pthread_kill.c:44:76
 #5 0x00007f12232969fc __pthread_kill_internal ./nptl/pthread_kill.c:78:10
 #6 0x00007f12232969fc pthread_kill ./nptl/pthread_kill.c:89:10
 #7 0x00007f1223242476 gsignal ./signal/../sysdeps/posix/raise.c:27:6
 #8 0x00007f12232287f3 abort ./stdlib/abort.c:81:7
 #9 0x00005566b4123733 llvm::report_fatal_error(llvm::Twine const&, bool) (/work/llvm/install/bin/llvm-lto2+0x6375733)
#10 0x00005566b4123586 (/work/llvm/install/bin/llvm-lto2+0x6375586)
#11 0x00005566b26d48c6 llvm::ARMTargetLowering::LowerCall(llvm::TargetLowering::CallLoweringInfo&, llvm::SmallVectorImpl<llvm::SDValue>&) const ARMISelLowering.cpp:0:0
#12 0x00005566b44ef594 llvm::TargetLowering::LowerCallTo(llvm::TargetLowering::CallLoweringInfo&) const (/work/llvm/install/bin/llvm-lto2+0x6741594)
#13 0x00005566b45108e2 llvm::SelectionDAGBuilder::lowerInvokable(llvm::TargetLowering::CallLoweringInfo&, llvm::BasicBlock const*) (/work/llvm/install/bin/llvm-lto2+0x67628e2)
#14 0x00005566b44f7cd5 llvm::SelectionDAGBuilder::LowerCallTo(llvm::CallBase const&, llvm::SDValue, bool, bool, llvm::BasicBlock const*, llvm::TargetLowering::PtrAuthInfo const*) (/work/llvm/install/bin/llvm-lto2+0x6749cd5)
#15 0x00005566b44e0a0e llvm::SelectionDAGBuilder::visitCall(llvm::CallInst const&) (/work/llvm/install/bin/llvm-lto2+0x6732a0e)
#16 0x00005566b44d363c llvm::SelectionDAGBuilder::visit(llvm::Instruction const&) (/work/llvm/install/bin/llvm-lto2+0x672563c)
#17 0x00005566b45926c6 llvm::SelectionDAGISel::SelectBasicBlock(llvm::ilist_iterator_w_bits<llvm::ilist_detail::node_options<llvm::Instruction, true, false, void, true, llvm::BasicBlock>, false, true>, llvm::ilist_iterator_w_bits<llvm::ilist_detail::node_options<llvm::Instruction, true, false, void, true, llvm::BasicBlock>, false, true>, bool&) (/work/llvm/install/bin/llvm-lto2+0x67e46c6)
#18 0x00005566b4591e3c llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) (/work/llvm/install/bin/llvm-lto2+0x67e3e3c)
#19 0x00005566b458f132 llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) (/work/llvm/install/bin/llvm-lto2+0x67e1132)
#20 0x00005566b27dfbc1 (anonymous namespace)::ARMDAGToDAGISel::runOnMachineFunction(llvm::MachineFunction&) ARMISelDAGToDAG.cpp:0:0
#21 0x00005566b458ca46 llvm::SelectionDAGISelLegacy::runOnMachineFunction(llvm::MachineFunction&) (/work/llvm/install/bin/llvm-lto2+0x67dea46)
#22 0x00005566b37c20d4 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (/work/llvm/install/bin/llvm-lto2+0x5a140d4)
#23 0x00005566b3d30999 llvm::FPPassManager::runOnFunction(llvm::Function&) (/work/llvm/install/bin/llvm-lto2+0x5f82999)
#24 0x00005566b3d38791 llvm::FPPassManager::runOnModule(llvm::Module&) (/work/llvm/install/bin/llvm-lto2+0x5f8a791)
#25 0x00005566b3d3141f llvm::legacy::PassManagerImpl::run(llvm::Module&) (/work/llvm/install/bin/llvm-lto2+0x5f8341f)
#26 0x00005566b3e14659 codegen(llvm::lto::Config const&, llvm::TargetMachine*, std::function<llvm::Expected<std::unique_ptr<llvm::CachedFileStream, std::default_delete<llvm::CachedFileStream>>> (unsigned int, llvm::Twine const&)>, unsigned int, llvm::Module&, llvm::ModuleSummaryIndex const&) LTOBackend.cpp:0:0
#27 0x00005566b3e134da llvm::lto::backend(llvm::lto::Config const&, std::function<llvm::Expected<std::unique_ptr<llvm::CachedFileStream, std::default_delete<llvm::CachedFileStream>>> (unsigned int, llvm::Twine const&)>, unsigned int, llvm::Module&, llvm::ModuleSummaryIndex&) (/work/llvm/install/bin/llvm-lto2+0x60654da)
#28 0x00005566b3df5547 llvm::lto::LTO::runRegularLTO(std::function<llvm::Expected<std::unique_ptr<llvm::CachedFileStream, std::default_delete<llvm::CachedFileStream>>> (unsigned int, llvm::Twine const&)>) (/work/llvm/install/bin/llvm-lto2+0x6047547)
#29 0x00005566b3df4aea llvm::lto::LTO::run(std::function<llvm::Expected<std::unique_ptr<llvm::CachedFileStream, std::default_delete<llvm::CachedFileStream>>> (unsigned int, llvm::Twine const&)>, std::function<llvm::Expected<std::function<llvm::Expected<std::unique_ptr<llvm::CachedFileStream, std::default_delete<llvm::CachedFileStream>>> (unsigned int, llvm::Twine const&)>> (unsigned int, llvm::StringRef, llvm::Twine const&)>) (/work/llvm/install/bin/llvm-lto2+0x6046aea)
#30 0x00005566b1e07cf3 run(int, char**) llvm-lto2.cpp:0:0
#31 0x00005566b1e02644 main (/work/llvm/install/bin/llvm-lto2+0x4054644)
#32 0x00007f1223229d90 __libc_start_call_main ./csu/../sysdeps/nptl/libc_start_call_main.h:58:16
#33 0x00007f1223229e40 call_init ./csu/../csu/libc-start.c:128:20
#34 0x00007f1223229e40 __libc_start_main ./csu/../csu/libc-start.c:379:5
#35 0x00005566b1dfed25 _start (/work/llvm/install/bin/llvm-lto2+0x4050d25)
./run.sh: line 13: 1466542 Aborted                 (core dumped) /work/llvm/install/bin/llvm-lto2 run part1.bc part2.bc -o test.o -r part1.bc,F90,pl -r part1.bc,F93,l -r part1.bc,F95,pl -r part1.bc,main,px -r part1.bc,init_0,l -r part1.bc,actual_fptrs,pl -r part2.bc,init_0,pl -r part2.bc,F93,pl
```

I think what's causing this to fail is that, going into the backend, `@F90` has a `nofpclass(nan inf)` attribute on its return value, but has a `musttail` call without that attribute. Removing the attribute from `@F90` or adding it to the call site causes the compile to succeed.

```
define internal nofpclass(nan inf) double @F90() unnamed_addr #0 {
entry:
  %0 = load ptr, ptr @fptrs, align 4, !tbaa !6
  %1 = icmp ne ptr %0, null, !nosanitize !10
  %2 = ptrtoint ptr %0 to i32, !nosanitize !10
  %3 = and i32 %2, 3, !nosanitize !10
  %4 = icmp eq i32 %3, 0, !nosanitize !10
  %5 = and i1 %1, %4, !nosanitize !10
  br i1 %5, label %cont1.i, label %trap.i, !nosanitize !10

trap.i:                                           ; preds = %entry
  tail call void @llvm.ubsantrap(i8 22) #4, !nosanitize !10
 unreachable, !nosanitize !10

cont1.i: ; preds = %entry
  %6 = load ptr, ptr @actual_fptrs, align 4, !tbaa !11
  %7 = ptrtoint ptr %6 to i32, !nosanitize !10
  %8 = and i32 %7, -2, !nosanitize !10
  %9 = inttoptr i32 %8 to ptr, !nosanitize !10
 %10 = getelementptr i8, ptr %9, i32 -8
  %11 = load i32, ptr %10, align 4, !nosanitize !10
  %12 = icmp eq i32 %11, -1056584962, !nosanitize !10
  br i1 %12, label %typecheck.i, label %cont4.i, !nosanitize !10

typecheck.i:                                      ; preds = %cont1.i
  %13 = getelementptr i8, ptr %9, i32 -4
  %14 = load i32, ptr %13, align 4, !nosanitize !10
  %15 = icmp eq i32 %14, -166727886, !nosanitize !10
  br i1 %15, label %cont4.i, label %trap2.i, !nosanitize !10

trap2.i:                                          ; preds = %typecheck.i
  tail call void @llvm.ubsantrap(i8 6) #4, !nosanitize !10
  unreachable, !nosanitize !10

cont4.i: ; preds = %typecheck.i, %cont1.i
  %call.i = musttail call double %6() #5
  ret double %call.i
}
```
</pre>
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