[llvm-dev] Hints needed for debugging an X86 backend bug.

[Wang, Pengfei via llvm-dev]

MachineInstr prints “UNKNOWN” only when “TII” in invalid. https://llvm.org/doxygen/MachineInstr_8cpp_source.html#l01669
It’s a bit strange that you generate IR using aarch64 while using X86 as backend. I think some target specific builtins won’t work, as well as many function attributes are not available.

Thanks
Pengfei

From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of Zhang via llvm-dev
Sent: Friday, August 20, 2021 11:05 AM
To: llvm-dev <llvm-dev at lists.llvm.org>
Subject: [llvm-dev] Hints needed for debugging an X86 backend bug.

Hi:
I have a IR file which has been reduced by bugpoint, the IR is originally compiled for X86_64 and has custom transforms applied.
It compiles fine if I set the triple to aarch64-arm-none-eabi, but crashes when using the X86 backend , results in the following stack trace:

```
Assertion failed: (itr != mi2iMap.end() && "Instruction not found in maps."), function getInstructionIndex, file LLVM/llvm/include/llvm/CodeGen/SlotIndexes.h, line 399.
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace.
Stack dump:
0.           Program arguments: bin/llc LLCCrash.bc -debug
1.           Running pass 'Function Pass Manager' on module 'LLCCrash.bc'.
2.           Running pass 'Simple Register Coalescing' on function '@_ZNK8CryptoPP15DL_VerifierBaseINS_8ECPPointEE17RecoverAndRestartEPhRNS_21PK_MessageAccumulatorE'
0  llc                      0x0000000103289eca llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 58
1  llc                      0x000000010328a459 PrintStackTraceSignalHandler(void*) + 25
2  llc                      0x000000010328832b llvm::sys::RunSignalHandlers() + 123
3  llc                      0x000000010328c209 SignalHandler(int) + 249
4  libsystem_platform.dylib 0x00007fff2052bd7d _sigtramp + 29
5  libdyld.dylib            0x00007fff20501473 dyldGlobalLockRelease() + 0
6  libsystem_c.dylib        0x00007fff2043a720 abort + 120
7  libsystem_c.dylib        0x00007fff204399d6 err + 0
8  llc                      0x0000000101e67066 llvm::SlotIndexes::getInstructionIndex(llvm::MachineInstr const&, bool) const + 470
9  llc                      0x0000000101e66e06 llvm::LiveIntervals::getInstructionIndex(llvm::MachineInstr const&) const + 38
10 llc                      0x0000000101ec5da5 (anonymous namespace)::RegisterCoalescer::joinCopy(llvm::MachineInstr*, bool&) + 149
11 llc                      0x0000000101ec2e5c (anonymous namespace)::RegisterCoalescer::copyCoalesceWorkList(llvm::MutableArrayRef<llvm::MachineInstr*>) + 204
12 llc                      0x0000000101ebdc34 (anonymous namespace)::RegisterCoalescer::joinAllIntervals() + 740
13 llc                      0x0000000101ebad54 (anonymous namespace)::RegisterCoalescer::runOnMachineFunction(llvm::MachineFunction&) + 804
```

The IR passes``opt -verify``, and given AArch64 backend works fine, I assume it's a bug in the X86 backend, thus I modified SlotIndexes::getInstructionIndex to print the MachineInstr:

```
 errs()<<"SlotIndex:\n";
 BundleNonDebug.dump();
```

which gives me:

```

SlotIndex:

  UNKNOWN , %59
```


I'm now absolutely lost on where this "UNKNOWN" comes from.



Zhang
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