[llvm] [AMDGPU] Handle memcpy()-like ops in LowerBufferFatPointers (PR #126621)

[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/20559

<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 :: CodeGen/AMDGPU/buffer-fat-pointers-memcpy.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 2: /b/1/llvm-x86_64-debian-dylib/build/bin/llc -mtriple=amdgcn -mcpu=gfx942 < /b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/CodeGen/AMDGPU/buffer-fat-pointers-memcpy.ll | /b/1/llvm-x86_64-debian-dylib/build/bin/FileCheck -check-prefix=SDAG-GFX942 /b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/CodeGen/AMDGPU/buffer-fat-pointers-memcpy.ll
+ /b/1/llvm-x86_64-debian-dylib/build/bin/FileCheck -check-prefix=SDAG-GFX942 /b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/CodeGen/AMDGPU/buffer-fat-pointers-memcpy.ll
+ /b/1/llvm-x86_64-debian-dylib/build/bin/llc -mtriple=amdgcn -mcpu=gfx942
/b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/CodeGen/AMDGPU/buffer-fat-pointers-memcpy.ll:270:21: error: SDAG-GFX942-NEXT: expected string not found in input
; SDAG-GFX942-NEXT: buffer_load_dwordx4 v[0:3], v60, s[4:7], 0 offen
                    ^
<stdin>:47:23: note: scanning from here
 v_mov_b32_e32 v60, s1
                      ^
<stdin>:49:2: note: possible intended match here
 buffer_load_dwordx4 v[4:7], v60, s[4:7], 0 offen offset:16
 ^
/b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/CodeGen/AMDGPU/buffer-fat-pointers-memcpy.ll:831:21: error: SDAG-GFX942-NEXT: is not on the line after the previous match
; SDAG-GFX942-NEXT: buffer_load_dwordx4 v[14:17], v1, s[4:7], 0 offen offset:48
                    ^
<stdin>:210:2: note: 'next' match was here
 buffer_load_dwordx4 v[14:17], v1, s[4:7], 0 offen offset:48
 ^
<stdin>:201:61: note: previous match ended here
 buffer_load_dwordx4 v[10:13], v1, s[4:7], 0 offen offset:32
                                                            ^
<stdin>:202:1: note: non-matching line after previous match is here
 v_add_u32_e32 v62, s8, v0
^
/b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/CodeGen/AMDGPU/buffer-fat-pointers-memcpy.ll:1190:21: error: SDAG-GFX942-NEXT: expected string not found in input
; SDAG-GFX942-NEXT: s_load_dwordx4 s[8:11], s[4:5], 0x24
                    ^
<stdin>:319:9: note: scanning from here
.LBB2_0:
        ^
<stdin>:320:2: note: possible intended match here
 s_load_dwordx4 s[0:3], s[4:5], 0x24
 ^

Input file: <stdin>
Check file: /b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/CodeGen/AMDGPU/buffer-fat-pointers-memcpy.ll

-dump-input=help explains the following input dump.

Input was:
<<<<<<
             .
             .
             .
            42:  s_mov_b32 s2, s9 
...

```

</details>

https://github.com/llvm/llvm-project/pull/126621