[llvm] [PGO] Ensure non-zero entry-count after `populateCounters` (PR #112029)

[Ellis Hoag via llvm-commits]

================
@@ -0,0 +1,28 @@
+; RUN: llvm-profdata merge %S/Inputs/fix_entry_count_sampled.proftext -o %t.profdata
----------------
ellishg wrote:

I think `split-file` was introduced relatively recently and `fix_entry_count.ll` was last updated 2 years ago. More recent proftext tests do use `split-file`.

https://github.com/llvm/llvm-project/blob/78e026f845fb4d924673a9d534cc36cf7b55473c/llvm/test/Transforms/Coroutines/coro-pgo-setbranchweights.ll#L1-L6

I like to use `split-file` because otherwise we have lots of similar `.proftext` files in `Inputs/` and it is slightly inconvenient to find their uses. It also means only one file needs to be updated if we want to change the test.

https://github.com/llvm/llvm-project/pull/112029