[llvm] [NVPTX] don't erase CopyToRegs when folding movs into loads (PR #149393)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-nvptx64-nvidia-ubuntu` running on `as-builder-7` while building `llvm` at step 6 "test-build-unified-tree-check-llvm".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/160/builds/21440

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

```
Step 6 (test-build-unified-tree-check-llvm) failure: test (failure)
******************** TEST 'LLVM :: CodeGen/NVPTX/pr126337.ll' FAILED ********************
Exit Code: 255

Command Output (stderr):
--
/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/bin/llc < /home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/llvm-project/llvm/test/CodeGen/NVPTX/pr126337.ll -mtriple=nvptx64 -mcpu=sm_70 | /home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/bin/FileCheck /home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/llvm-project/llvm/test/CodeGen/NVPTX/pr126337.ll # RUN: at line 2
+ /home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/bin/llc -mtriple=nvptx64 -mcpu=sm_70
+ /home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/bin/FileCheck /home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/llvm-project/llvm/test/CodeGen/NVPTX/pr126337.ll
/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/bin/llc < /home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/llvm-project/llvm/test/CodeGen/NVPTX/pr126337.ll -mtriple=nvptx64 -mcpu=sm_70 | /usr/local/cuda/bin/ptxas -arch=sm_60 -c - # RUN: at line 3
+ /home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/bin/llc -mtriple=nvptx64 -mcpu=sm_70
+ /usr/local/cuda/bin/ptxas -arch=sm_60 -c -
ptxas fatal   : SM version specified by .target is higher than default SM version assumed

--

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


```

</details>

https://github.com/llvm/llvm-project/pull/149393