[llvm] Reland [NFC] Move DroppedVariableStats to its own file and redesign it to be extensible. (PR #117042)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-ppc64-aix` running on `aix-ppc64` while building `llvm` at step 3 "clean-build-dir".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/64/builds/1612

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

```
Step 3 (clean-build-dir) failure: Delete failed. (failure) (timed out)
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'Profile-powerpc :: ContinuousSyncMode/online-merging.c' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 6: rm -rf /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir && mkdir -p /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir && cd /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir
+ rm -rf /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir
+ mkdir -p /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir
+ cd /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir
RUN: at line 9: echo "void dso1(void) {}" > dso1.c
+ echo 'void dso1(void) {}'
RUN: at line 10: echo "void dso2(void) {}" > dso2.c
+ echo 'void dso2(void) {}'
RUN: at line 11: /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/./bin/clang   -m32   -fprofile-generate -mllvm -runtime-counter-relocation -shared -o /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/dso1.dylib dso1.c -fprofile-update=atomic
+ /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/./bin/clang -m32 -fprofile-generate -mllvm -runtime-counter-relocation -shared -o /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/dso1.dylib dso1.c -fprofile-update=atomic
RUN: at line 12: /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/./bin/clang   -m32   -fprofile-generate -mllvm -runtime-counter-relocation -shared -o /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/dso2.dylib dso2.c -fprofile-update=atomic
+ /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/./bin/clang -m32 -fprofile-generate -mllvm -runtime-counter-relocation -shared -o /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/dso2.dylib dso2.c -fprofile-update=atomic
RUN: at line 13: /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/./bin/clang   -m32   -fprofile-generate -mllvm -runtime-counter-relocation -o main.exe /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/llvm-project/compiler-rt/test/profile/ContinuousSyncMode/online-merging.c /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/dso1.dylib /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/dso2.dylib -fprofile-update=atomic
+ /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/./bin/clang -m32 -fprofile-generate -mllvm -runtime-counter-relocation -o main.exe /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/llvm-project/compiler-rt/test/profile/ContinuousSyncMode/online-merging.c /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/dso1.dylib /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/dso2.dylib -fprofile-update=atomic
RUN: at line 18: env LLVM_PROFILE_FILE="/home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/profdir/%m%c.profraw"  /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/main.exe nospawn
+ env LLVM_PROFILE_FILE=/home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/profdir/%m%c.profraw /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/main.exe nospawn
RUN: at line 19: llvm-profdata merge -o /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.profdata /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/profdir
+ llvm-profdata merge -o /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.profdata /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/profdir
RUN: at line 20: llvm-profdata show --counts --all-functions /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.profdata | FileCheck /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/llvm-project/compiler-rt/test/profile/ContinuousSyncMode/online-merging.c -check-prefix=ROUND1
+ llvm-profdata show --counts --all-functions /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.profdata
+ FileCheck /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/llvm-project/compiler-rt/test/profile/ContinuousSyncMode/online-merging.c -check-prefix=ROUND1
RUN: at line 42: env LLVM_PROFILE_FILE="/home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/profdir/%m%c.profraw"  /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/main.exe spawn 'LLVM_PROFILE_FILE=/home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/profdir/%m%c.profraw'
+ env LLVM_PROFILE_FILE=/home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/profdir/%m%c.profraw /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/main.exe spawn LLVM_PROFILE_FILE=/home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/profdir/%m%c.profraw
RUN: at line 43: llvm-profdata merge -o /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.profdata /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/profdir
+ llvm-profdata merge -o /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.profdata /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.dir/profdir
RUN: at line 44: llvm-profdata show --counts --all-functions /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.profdata | FileCheck /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/llvm-project/compiler-rt/test/profile/ContinuousSyncMode/online-merging.c -check-prefix=ROUND2
+ llvm-profdata show --counts --all-functions /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/build/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc/ContinuousSyncMode/Output/online-merging.c.tmp.profdata
+ FileCheck /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/llvm-project/compiler-rt/test/profile/ContinuousSyncMode/online-merging.c -check-prefix=ROUND2
/home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/llvm-project/compiler-rt/test/profile/ContinuousSyncMode/online-merging.c:54:16: error: ROUND2-DAG: expected string not found in input
// ROUND2-DAG: Block counts: [97]
               ^
<stdin>:9:20: note: scanning from here
 Block counts: [97]
                   ^
<stdin>:13:2: note: possible intended match here
 Block counts: [96]
 ^

Input file: <stdin>
Check file: /home/powerllvm/powerllvm_env/aix-ppc64/clang-ppc64-aix/llvm-project/compiler-rt/test/profile/ContinuousSyncMode/online-merging.c

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

Input was:
<<<<<<
...

```

</details>

https://github.com/llvm/llvm-project/pull/117042