[llvm] InstCombine: Add baseline test for fcmp-0-select combine (PR #172380)

[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/31965

<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/select-fcmp-fmul-zero-absorbing-value.ll' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 2
/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/bin/opt -S -p=instcombine < /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/Transforms/InstCombine/select-fcmp-fmul-zero-absorbing-value.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/Transforms/InstCombine/select-fcmp-fmul-zero-absorbing-value.ll
# executed command: /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/bin/opt -S -p=instcombine
# note: command had no output on stdout or stderr
# executed command: /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/Transforms/InstCombine/select-fcmp-fmul-zero-absorbing-value.ll
# .---command stderr------------
# | /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/Transforms/InstCombine/select-fcmp-fmul-zero-absorbing-value.ll:376:15: error: CHECK-NEXT: expected string not found in input
# | ; CHECK-NEXT: [[MUL_FABS_X:%.*]] = fmul float [[FABS_X]], 0x4170000000000000
# |               ^
# | <stdin>:179:52: note: scanning from here
# |  %fabs.x = call nnan float @llvm.fabs.f32(float %x)
# |                                                    ^
# | <stdin>:179:52: note: with "FABS_X" equal to "%fabs.x"
# |  %fabs.x = call nnan float @llvm.fabs.f32(float %x)
# |                                                    ^
# | <stdin>:180:21: note: possible intended match here
# |  %mul.fabs.x = fmul nnan float %fabs.x, 0x4170000000000000
# |                     ^
# | 
# | Input file: <stdin>
# | Check file: /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/Transforms/InstCombine/select-fcmp-fmul-zero-absorbing-value.ll
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |              1: ; ModuleID = '<stdin>' 
# |              2: source_filename = "<stdin>" 
# |              3:  
# |              4: define float @select_oeq_fmul_fabs_or_fabs_src(float %x) { 
# | label:5'0       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | label:5'1       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | same:6'0                                                       ^~~~~~~~~~~
# | same:6'1                                                             ^~     captured var "X"
# |              5:  %fabs.x = call float @llvm.fabs.f32(float %x) 
# | next:7'0         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | next:7'1                                                        with "X" equal to "%x"
# | next:7'2         ^~~~~~~                                        captured var "FABS_X"
# |              6:  %mul.fabs.x = fmul float %fabs.x, 0x4170000000000000 
# | next:8'0         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | next:8'1                                                               with "FABS_X" equal to "%fabs.x"
# | next:8'2         ^~~~~~~~~~~                                           captured var "MUL_FABS_X"
# |              7:  %x.is.zero = fcmp oeq float %x, 0.000000e+00 
# | next:9'0         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | next:9'1                                                       with "X" equal to "%x"
...

```

</details>

https://github.com/llvm/llvm-project/pull/172380