[llvm] AMDGPU: Add codegen for atomicrmw operations usub_cond and usub_sat (PR #141068)

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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/test/CodeGen/AMDGPU/atomicrmw_usub_cond.ll llvm/test/CodeGen/AMDGPU/atomicrmw_usub_sat.ll llvm/test/CodeGen/AMDGPU/buffer-fat-pointer-atomicrmw-usub_cond.ll llvm/test/CodeGen/AMDGPU/buffer-fat-pointer-atomicrmw-usub_sat.ll llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp llvm/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp llvm/lib/Target/AMDGPU/GCNSubtarget.h llvm/lib/Target/AMDGPU/R600ISelLowering.cpp llvm/lib/Target/AMDGPU/SIISelLowering.cpp llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp llvm/test/CodeGen/AMDGPU/GlobalISel/llvm.amdgcn.global.atomic.csub.ll llvm/test/CodeGen/AMDGPU/atomics_cond_sub.ll llvm/test/CodeGen/AMDGPU/cgp-addressing-modes-gfx1030.ll llvm/test/CodeGen/AMDGPU/global-saddr-atomics.gfx1030.ll llvm/test/CodeGen/AMDGPU/llvm.amdgcn.global.atomic.csub.ll llvm/test/CodeGen/AMDGPU/private-memory-atomics.ll llvm/test/CodeGen/AMDGPU/shl_add_ptr_csub.ll llvm/test/Transforms/AtomicExpand/AMDGPU/expand-atomic-i16-system.ll llvm/test/Transforms/AtomicExpand/AMDGPU/expand-atomic-i16.ll llvm/test/Transforms/AtomicExpand/AMDGPU/expand-atomic-i32-agent.ll llvm/test/Transforms/AtomicExpand/AMDGPU/expand-atomic-i32-system.ll llvm/test/Transforms/AtomicExpand/AMDGPU/expand-atomic-i64-agent.ll llvm/test/Transforms/AtomicExpand/AMDGPU/expand-atomic-i64-system.ll llvm/test/Transforms/AtomicExpand/AMDGPU/expand-atomic-i8-system.ll llvm/test/Transforms/AtomicExpand/AMDGPU/expand-atomic-i8.ll
``````````

</details>


The following files introduce new uses of undef:
 - llvm/test/CodeGen/AMDGPU/atomicrmw_usub_cond.ll
 - llvm/test/CodeGen/AMDGPU/atomicrmw_usub_sat.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/141068