[clang] [llvm] [AMDGPU] Add initial support for VGPR as memory (PR #205435)

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github-actions[bot] wrote:

<!--LLVM CODE FORMAT COMMENT: {undef deprecator}-->


:warning: undef deprecator found issues in your code. :warning:

<details>
<summary>
You can test this locally with the following command:
</summary>

``````````bash
git diff -U0 --pickaxe-regex -S '([^a-zA-Z0-9#_-]undef([^a-zA-Z0-9_-]|$)|UndefValue::get)' 'HEAD~1' HEAD llvm/lib/Target/AMDGPU/AMDGPULowerModuleVGPRs.cpp llvm/lib/Target/AMDGPU/AMDGPUPrivateObjectVGPRs.cpp llvm/test/CodeGen/AMDGPU/vgpr-as-memory-dynamic.ll llvm/test/CodeGen/AMDGPU/vgpr-as-memory-lower-module.ll llvm/test/CodeGen/AMDGPU/vgpr-as-memory-subdword.ll llvm/test/CodeGen/AMDGPU/vgpr-as-memory.ll llvm/test/Verifier/AMDGPU/vgpr-memory.ll clang/include/clang/Sema/SemaAMDGPU.h clang/lib/CodeGen/CGDecl.cpp clang/lib/Sema/SemaAMDGPU.cpp clang/lib/Sema/SemaDeclAttr.cpp clang/test/CodeGen/target-data.c llvm/include/llvm/Support/AMDGPUAddrSpace.h llvm/lib/IR/AutoUpgrade.cpp llvm/lib/IR/Verifier.cpp llvm/lib/IR/VerifierAMDGPU.cpp llvm/lib/IR/VerifierInternal.h llvm/lib/Target/AMDGPU/AMDGPU.h llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.h llvm/lib/Target/AMDGPU/AMDGPUPromoteAlloca.cpp llvm/lib/Target/AMDGPU/AMDGPUResourceUsageAnalysis.cpp llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp llvm/lib/Target/AMDGPU/SIISelLowering.cpp llvm/lib/Target/AMDGPU/SIISelLowering.h llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.cpp llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp llvm/lib/Target/AMDGPU/SIRegisterInfo.h llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.h llvm/lib/TargetParser/TargetDataLayout.cpp llvm/test/CodeGen/AMDGPU/llc-pipeline-npm.ll llvm/test/CodeGen/AMDGPU/llc-pipeline.ll llvm/test/CodeGen/AMDGPU/nullptr.ll llvm/test/CodeGen/AMDGPU/sgpr-regalloc-flags.ll llvm/test/Verifier/AMDGPU/alloca.ll llvm/unittests/Bitcode/DataLayoutUpgradeTest.cpp
``````````

</details>


The following files introduce new uses of undef:
 - clang/lib/CodeGen/CGDecl.cpp
 - llvm/test/CodeGen/AMDGPU/vgpr-as-memory-dynamic.ll
 - llvm/test/CodeGen/AMDGPU/vgpr-as-memory-lower-module.ll
 - llvm/test/CodeGen/AMDGPU/vgpr-as-memory-subdword.ll
 - llvm/test/CodeGen/AMDGPU/vgpr-as-memory.ll
 - llvm/test/Verifier/AMDGPU/vgpr-memory.ll

[Undef](https://llvm.org/docs/LangRef.html#undefined-values) is now deprecated and should only be used in the rare cases where no replacement is possible. For example, a load of uninitialized memory yields `undef`. You should use `poison` values for placeholders instead.

In tests, avoid using `undef` and having tests that trigger undefined behavior. If you need an operand with some unimportant value, you can add a new argument to the function and use that instead.

For example, this is considered a bad practice:
```llvm
define void @fn() {
  ...
  br i1 undef, ...
}
```

Please use the following instead:
```llvm
define void @fn(i1 %cond) {
  ...
  br i1 %cond, ...
}
```

Please refer to the [Undefined Behavior Manual](https://llvm.org/docs/UndefinedBehavior.html) for more information.



https://github.com/llvm/llvm-project/pull/205435