[llvm] [MIR] Serialize virtual register flags (PR #110228)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `lld-x86_64-ubuntu-fast` running on `as-builder-4` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/33/builds/4697

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: CodeGen/AArch64/GlobalISel/call-translator.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 1: /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/llc -mtriple=aarch64-linux-gnu -O0 -stop-after=irtranslator -global-isel -verify-machineinstrs /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/CodeGen/AArch64/GlobalISel/call-translator.ll -o - 2>&1 | /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/FileCheck /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/CodeGen/AArch64/GlobalISel/call-translator.ll
+ /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/llc -mtriple=aarch64-linux-gnu -O0 -stop-after=irtranslator -global-isel -verify-machineinstrs /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/CodeGen/AArch64/GlobalISel/call-translator.ll -o -
+ /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/FileCheck /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/CodeGen/AArch64/GlobalISel/call-translator.ll
/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/CodeGen/AArch64/GlobalISel/call-translator.ll:38:10: error: CHECK: expected string not found in input
; CHECK: - { id: [[FUNC:[0-9]+]], class: gpr64, preferred-register: '' }
         ^
<stdin>:402:11: note: scanning from here
registers:
          ^
<stdin>:403:2: note: possible intended match here
 - { id: 0, class: gpr64, preferred-register: '', flags: [ ] }
 ^

Input file: <stdin>
Check file: /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/CodeGen/AArch64/GlobalISel/call-translator.ll

-dump-input=help explains the following input dump.

Input was:
<<<<<<
            .
            .
            .
          397: hasEHFunclets: false 
          398: isOutlined: false 
          399: debugInstrRef: false 
          400: failsVerification: false 
          401: tracksDebugUserValues: false 
          402: registers: 
check:38'0               X error: no match found
          403:  - { id: 0, class: gpr64, preferred-register: '', flags: [ ] } 
check:38'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
check:38'1      ?                                                              possible intended match
          404: liveins: 
check:38'0     ~~~~~~~~~
          405:  - { reg: '$x0', virtual-reg: '' } 
check:38'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          406: frameInfo: 
check:38'0     ~~~~~~~~~~~
          407:  isFrameAddressTaken: false 
check:38'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          408:  isReturnAddressTaken: false 
check:38'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            .
            .
...

```

</details>

https://github.com/llvm/llvm-project/pull/110228