[llvm] [InstCombine] simplify `icmp pred x, ~x` (PR #73990)

[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 `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/95/builds/9313

<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 :: Transforms/InstCombine/icmp-of-xor-x.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 2: /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/build/bin/opt < /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/llvm/test/Transforms/InstCombine/icmp-of-xor-x.ll -passes=instcombine -S | /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/Transforms/InstCombine/icmp-of-xor-x.ll
+ /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/build/bin/opt -passes=instcombine -S
+ /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/Transforms/InstCombine/icmp-of-xor-x.ll
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/llvm/test/Transforms/InstCombine/icmp-of-xor-x.ll:127:15: error: CHECK-NEXT: expected string not found in input
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt <2 x i8> [[X:%.*]], <i8 -1, i8 -1>
              ^
<stdin>:66:30: note: scanning from here
define <2 x i1> @src_sgt_vec(<2 x i8> %x) {
                             ^
<stdin>:67:2: note: possible intended match here
 %cmp = icmp sgt <2 x i8> %x, splat (i8 -1)
 ^
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/llvm/test/Transforms/InstCombine/icmp-of-xor-x.ll:148:15: error: CHECK-NEXT: expected string not found in input
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt <2 x i8> [[X:%.*]], <i8 -1, i8 -1>
              ^
<stdin>:76:30: note: scanning from here
define <2 x i1> @src_sge_vec(<2 x i8> %x) {
                             ^
<stdin>:77:2: note: possible intended match here
 %cmp = icmp sgt <2 x i8> %x, splat (i8 -1)
 ^
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/llvm/test/Transforms/InstCombine/icmp-of-xor-x.ll:169:15: error: CHECK-NEXT: expected string not found in input
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt <2 x i8> [[X:%.*]], <i8 -1, i8 -1>
              ^
<stdin>:86:30: note: scanning from here
define <2 x i1> @src_ult_vec(<2 x i8> %x) {
                             ^
<stdin>:87:2: note: possible intended match here
 %cmp = icmp sgt <2 x i8> %x, splat (i8 -1)
 ^
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/llvm/test/Transforms/InstCombine/icmp-of-xor-x.ll:190:15: error: CHECK-NEXT: expected string not found in input
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt <2 x i8> [[X:%.*]], <i8 -1, i8 -1>
              ^
<stdin>:96:30: note: scanning from here
define <2 x i1> @src_ule_vec(<2 x i8> %x) {
                             ^
<stdin>:97:2: note: possible intended match here
 %cmp = icmp sgt <2 x i8> %x, splat (i8 -1)
 ^
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/llvm/test/Transforms/InstCombine/icmp-of-xor-x.ll:200:15: error: CHECK-NEXT: expected string not found in input
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt <2 x i8> [[X:%.*]], <i8 -1, i8 -1>
              ^
<stdin>:101:34: note: scanning from here
define <2 x i1> @src_ule_vec_min(<2 x i8> %x) {
                                 ^
...

```

</details>

https://github.com/llvm/llvm-project/pull/73990