[llvm] MIR: Serialize MachineBasicBlock::MaxBytesForAlignment (PR #227139)

[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/46076

<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/AMDGPU/loop-header-align-gfx950.mir' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 2
/home/buildbot/worker/lld-x86_64/build/bin/llc -mtriple=amdgpu9.50 -run-pass=block-placement -o - /home/buildbot/worker/lld-x86_64/llvm-project/llvm/test/CodeGen/AMDGPU/loop-header-align-gfx950.mir | /home/buildbot/worker/lld-x86_64/build/bin/FileCheck /home/buildbot/worker/lld-x86_64/llvm-project/llvm/test/CodeGen/AMDGPU/loop-header-align-gfx950.mir
# executed command: /home/buildbot/worker/lld-x86_64/build/bin/llc -mtriple=amdgpu9.50 -run-pass=block-placement -o - /home/buildbot/worker/lld-x86_64/llvm-project/llvm/test/CodeGen/AMDGPU/loop-header-align-gfx950.mir
# executed command: /home/buildbot/worker/lld-x86_64/build/bin/FileCheck /home/buildbot/worker/lld-x86_64/llvm-project/llvm/test/CodeGen/AMDGPU/loop-header-align-gfx950.mir
# .---command stderr------------
# | /home/buildbot/worker/lld-x86_64/llvm-project/llvm/test/CodeGen/AMDGPU/loop-header-align-gfx950.mir:26:16: error: CHECK-NEXT: expected string not found in input
# |  ; CHECK-NEXT: bb.1 (align 32):
# |                ^
# | <stdin>:139:2: note: scanning from here
# |  
# |  ^
# | <stdin>:140:2: note: possible intended match here
# |  bb.1 (align 32, max-bytes-for-alignment 4):
# |  ^
# | /home/buildbot/worker/lld-x86_64/llvm-project/llvm/test/CodeGen/AMDGPU/loop-header-align-gfx950.mir:239:16: error: CHECK-NEXT: expected string not found in input
# |  ; CHECK-NEXT: bb.6 (align 32):
# |                ^
# | <stdin>:558:2: note: scanning from here
# |  
# |  ^
# | <stdin>:559:2: note: possible intended match here
# |  bb.6 (align 32, max-bytes-for-alignment 4):
# |  ^
# | 
# | Input file: <stdin>
# | Check file: /home/buildbot/worker/lld-x86_64/llvm-project/llvm/test/CodeGen/AMDGPU/loop-header-align-gfx950.mir
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |             .
# |             .
# |             .
# |           134:  bb.0: 
# |           135:  successors: %bb.1(0x80000000) 
# |           136:  liveins: $vgpr0_vgpr1 
# |           137:   
# |           138:  renamable $sgpr0_sgpr1 = S_MOV_B64 0 
# |           139:   
# | next:26'0      {   search range start (exclusive)
# | next:26'1          error: no match found in search range
# |           140:  bb.1 (align 32, max-bytes-for-alignment 4): 
# | next:26'2       ?                                             possible intended match
# |           141:  successors: %bb.2(0x04000000), %bb.1(0x7c000000) 
...

```

</details>

https://github.com/llvm/llvm-project/pull/227139