[llvm] [AMDGPU][True16][MC] validate op_sel and .l/.h syntax (PR #123250)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-x86_64-debian-dylib` running on `gribozavr4` while building `llvm` at step 7 "test-build-unified-tree-check-llvm".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/60/builds/18446

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

```
Step 7 (test-build-unified-tree-check-llvm) failure: test (failure)
******************** TEST 'LLVM :: MC/AMDGPU/gfx11_asm_vop3_from_vopc.s' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
RUN: at line 2: not /b/1/llvm-x86_64-debian-dylib/build/bin/llvm-mc -triple=amdgcn -mcpu=gfx1100 -mattr=+wavefrontsize32,+real-true16 -show-encoding /b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/MC/AMDGPU/gfx11_asm_vop3_from_vopc.s | /b/1/llvm-x86_64-debian-dylib/build/bin/FileCheck --check-prefixes=GFX11,W32 /b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/MC/AMDGPU/gfx11_asm_vop3_from_vopc.s
+ not /b/1/llvm-x86_64-debian-dylib/build/bin/llvm-mc -triple=amdgcn -mcpu=gfx1100 -mattr=+wavefrontsize32,+real-true16 -show-encoding /b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/MC/AMDGPU/gfx11_asm_vop3_from_vopc.s
+ /b/1/llvm-x86_64-debian-dylib/build/bin/FileCheck --check-prefixes=GFX11,W32 /b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/MC/AMDGPU/gfx11_asm_vop3_from_vopc.s
llvm-mc: /b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/include/llvm/ADT/SmallVector.h:295: llvm::SmallVectorTemplateCommon::const_reference llvm::SmallVectorTemplateCommon<llvm::MCOperand, void>::operator[](llvm::SmallVectorTemplateCommon::size_type) const [T = llvm::MCOperand]: Assertion `idx < size()' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.	Program arguments: /b/1/llvm-x86_64-debian-dylib/build/bin/llvm-mc -triple=amdgcn -mcpu=gfx1100 -mattr=+wavefrontsize32,+real-true16 -show-encoding /b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/MC/AMDGPU/gfx11_asm_vop3_from_vopc.s
 #0 0x00007f652a7e8007 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/b/1/llvm-x86_64-debian-dylib/build/lib/libLLVM.so.21.0git+0xf81007)
 #1 0x00007f652a7e5abe llvm::sys::RunSignalHandlers() (/b/1/llvm-x86_64-debian-dylib/build/lib/libLLVM.so.21.0git+0xf7eabe)
 #2 0x00007f652a7e86df SignalHandler(int) Signals.cpp:0:0
 #3 0x00007f6529851140 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x13140)
 #4 0x00007f6529377d51 raise (/lib/x86_64-linux-gnu/libc.so.6+0x38d51)
 #5 0x00007f6529361537 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22537)
 #6 0x00007f652936140f (/lib/x86_64-linux-gnu/libc.so.6+0x2240f)
 #7 0x00007f65293706d2 (/lib/x86_64-linux-gnu/libc.so.6+0x316d2)
 #8 0x00007f652d8d3da7 (anonymous namespace)::AMDGPUAsmParser::validateInstruction(llvm::MCInst const&, llvm::SMLoc const&, llvm::SmallVectorImpl<std::unique_ptr<llvm::MCParsedAsmOperand, std::default_delete<llvm::MCParsedAsmOperand>>> const&) AMDGPUAsmParser.cpp:0:0
 #9 0x00007f652d89e3f5 (anonymous namespace)::AMDGPUAsmParser::matchAndEmitInstruction(llvm::SMLoc, unsigned int&, llvm::SmallVectorImpl<std::unique_ptr<llvm::MCParsedAsmOperand, std::default_delete<llvm::MCParsedAsmOperand>>>&, llvm::MCStreamer&, unsigned long&, bool) AMDGPUAsmParser.cpp:0:0
#10 0x00007f652c872abb (anonymous namespace)::AsmParser::parseAndMatchAndEmitTargetInstruction((anonymous namespace)::ParseStatementInfo&, llvm::StringRef, llvm::AsmToken, llvm::SMLoc) AsmParser.cpp:0:0
#11 0x00007f652c8654a6 (anonymous namespace)::AsmParser::parseStatement((anonymous namespace)::ParseStatementInfo&, llvm::MCAsmParserSemaCallback*) AsmParser.cpp:0:0
#12 0x00007f652c85ddb2 (anonymous namespace)::AsmParser::Run(bool, bool) AsmParser.cpp:0:0
#13 0x000000000040bbf6 main (/b/1/llvm-x86_64-debian-dylib/build/bin/llvm-mc+0x40bbf6)
#14 0x00007f6529362d7a __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x23d7a)
#15 0x0000000000408bca _start (/b/1/llvm-x86_64-debian-dylib/build/bin/llvm-mc+0x408bca)
error: Aborted
FileCheck error: '<stdin>' is empty.
FileCheck command line:  /b/1/llvm-x86_64-debian-dylib/build/bin/FileCheck --check-prefixes=GFX11,W32 /b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/MC/AMDGPU/gfx11_asm_vop3_from_vopc.s

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/123250