[llvm] [AArch64] Improve lowering of scalar abs(sub(a, b)). (PR #151180)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-gcc-ubuntu` running on `sie-linux-worker3` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/174/builds/22358

<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/AArch64/midpoint-int.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/bin/llc -mtriple=aarch64-unknown-linux-gnu < /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/CodeGen/AArch64/midpoint-int.ll | /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/bin/FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/CodeGen/AArch64/midpoint-int.ll # RUN: at line 2
+ /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/bin/llc -mtriple=aarch64-unknown-linux-gnu
+ /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/bin/FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/CodeGen/AArch64/midpoint-int.ll
/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/CodeGen/AArch64/midpoint-int.ll:304:15: error: CHECK-NEXT: expected string not found in input
; CHECK-NEXT: sxth w9, w1
              ^
<stdin>:197:10: note: scanning from here
// %bb.0:
         ^
<stdin>:200:7: note: possible intended match here
 subs w10, w9, w1, sxth
      ^
/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/CodeGen/AArch64/midpoint-int.ll:429:15: error: CHECK-NEXT: expected string not found in input
; CHECK-NEXT: sxtb w9, w1
              ^
<stdin>:279:10: note: scanning from here
// %bb.0:
         ^
<stdin>:282:7: note: possible intended match here
 subs w10, w9, w1, sxtb
      ^

Input file: <stdin>
Check file: /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/CodeGen/AArch64/midpoint-int.ll

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

Input was:
<<<<<<
             1:  .file "<stdin>" 
             2:  .text 
             3:  .globl scalar_i32_signed_reg_reg // -- Begin function scalar_i32_signed_reg_reg 
             4:  .p2align 2 
             5:  .type scalar_i32_signed_reg_reg, at function 
             6: scalar_i32_signed_reg_reg: // @scalar_i32_signed_reg_reg 
label:14'0      ^~~~~~~~~~~~~~~~~~~~~~~~~~
label:14'1      ^~~~~~~~~~~~~~~~~~~~~~~~~~
             7: // %bb.0: 
check:15        ^~~~~~~~~
             8:  subs w9, w0, w1 
next:16          ^~~~~~~~~~~~~~~
             9:  mov w8, #-1 // =0xffffffff 
next:17          ^~~~~~~~~~~~~~~~~~~~~~~~~~
            10:  cneg w9, w9, le 
next:18          ^~~~~~~~~~~~~~~
...

```

</details>

https://github.com/llvm/llvm-project/pull/151180