[clang] [OpenMP] Restore loop variable values after loop-tranformation constructs. (PR #208533)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `openmp-s390x-linux` running on `systemz-1` while building `clang` at step 6 "test-openmp".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/88/builds/24941

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

```
Step 6 (test-openmp) failure: test (failure)
******************** TEST 'libomp :: transform/reverse/iterfor.cpp' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
/home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.build/./bin/clang++ -fopenmp   -I /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/src -I /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test -L /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/src  -fno-omit-frame-pointer -mbackchain -I /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/ompt -std=c++20 /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/transform/reverse/iterfor.cpp -o /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/transform/reverse/Output/iterfor.cpp.tmp -lm -latomic && /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/transform/reverse/Output/iterfor.cpp.tmp | tee /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/transform/reverse/Output/iterfor.cpp.tmp.out | /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.build/./bin/FileCheck /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/transform/reverse/iterfor.cpp --match-full-lines
# executed command: /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.build/./bin/clang++ -fopenmp -I /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/src -I /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test -L /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/src -fno-omit-frame-pointer -mbackchain -I /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/ompt -std=c++20 /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/transform/reverse/iterfor.cpp -o /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/transform/reverse/Output/iterfor.cpp.tmp -lm -latomic
# executed command: /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/transform/reverse/Output/iterfor.cpp.tmp
# executed command: tee /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/transform/reverse/Output/iterfor.cpp.tmp.out
# executed command: /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.build/./bin/FileCheck /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/transform/reverse/iterfor.cpp --match-full-lines
# .---command stderr------------
# | /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/transform/reverse/iterfor.cpp:160:16: error: CHECK-NEXT: is not on the line after the previous match
# | // CHECK-NEXT: [range] iterator dtor
# |                ^
# | <stdin>:25:1: note: 'next' match was here
# | [range] iterator dtor
# | ^
# | <stdin>:21:22: note: previous match ended here
# | [range] iterator dtor
# |                      ^
# | <stdin>:22:1: note: non-matching line after previous match is here
# | [range] iterator distance: 3
# | ^
# | 
# | Input file: <stdin>
# | Check file: /home/buildbot/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/transform/reverse/iterfor.cpp
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |             .
# |             .
# |             .
# |            16: [range] iterator dtor 
# |            17: [range] iterator advance: 0 += 0 
# |            18: [range] iterator move assign 
# |            19: [range] iterator deref: 0 
# |            20: v=0 
# |            21: [range] iterator dtor 
# | next:160'0                         {   search range start (exclusive)
# |            22: [range] iterator distance: 3 
# |            23: [range] iterator advance: 0 += 3 
# |            24: [range] iterator move assign 
# |            25: [range] iterator dtor 
# | next:160'1     !~~~~~~~~~~~~~~~~~~~~   error: match on wrong line
# |            26: [range] iterator dtor 
# |            27: [range] iterator dtor 
# |            28: done 
...

```

</details>

https://github.com/llvm/llvm-project/pull/208533