[clang] [llvm] [NVPTX] Support i256 load/store with 256-bit vector load (PR #155198)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-ppc64le-linux-test-suite` running on `ppc64le-clang-test-suite` while building `clang,llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/95/builds/17650

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

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: CodeGen/NVPTX/load-store-atomic.err.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
not /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/build/bin/llc < /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/llvm/test/CodeGen/NVPTX/load-store-atomic.err.ll -march=nvptx64 -mcpu=sm_100 -mattr=+ptx88 2>&1 | /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/build/bin/FileCheck /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/llvm/test/CodeGen/NVPTX/load-store-atomic.err.ll # RUN: at line 1
+ not /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/build/bin/llc -march=nvptx64 -mcpu=sm_100 -mattr=+ptx88
+ /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/build/bin/FileCheck /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/llvm/test/CodeGen/NVPTX/load-store-atomic.err.ll
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/llvm/test/CodeGen/NVPTX/load-store-atomic.err.ll:5:10: error: CHECK: expected string not found in input
; CHECK: error: unsupported atomic store
         ^
<stdin>:2:31: note: scanning from here
error: unsupported atomic load
                              ^
<stdin>:11:69: note: possible intended match here
 // .globl test_i128_generic_atomic // -- Begin function test_i128_generic_atomic
                                                                    ^

Input file: <stdin>
Check file: /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/llvm/test/CodeGen/NVPTX/load-store-atomic.err.ll

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

Input was:
<<<<<<
           1: error: unsupported atomic store 
           2: error: unsupported atomic load 
check:5'0                                   X error: no match found
           3: // 
check:5'0     ~~~
           4: // Generated by LLVM NVPTX Back-End 
check:5'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           5: // 
check:5'0     ~~~
           6:  
check:5'0     ~
           7: .version 8.8 
check:5'0     ~~~~~~~~~~~~~
           8: .target sm_100 
check:5'0     ~~~~~~~~~~~~~~~
           9: .address_size 64 
check:5'0     ~~~~~~~~~~~~~~~~~
          10:  
check:5'0     ~
          11:  // .globl test_i128_generic_atomic // -- Begin function test_i128_generic_atomic 
check:5'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
check:5'1                                                                         ?              possible intended match
          12:  // @test_i128_generic_atomic 
check:5'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          13: .visible .func test_i128_generic_atomic( 
...

```

</details>

https://github.com/llvm/llvm-project/pull/155198