[llvm] [InstrProf] Support conditional counter updates (PR #102542)

[via llvm-commits]

gulfemsavrun wrote:

> > reduce the write contention by first checking whether the counter is set before overwriting it.
> 
> any result to share on runtime overhead?
As @alanzhao1 mentioned, this is motivated based on the Chromium results, and I'm interested in testing this in Fuchsia. I can provide more results when we roll this change into our toolchain.


https://github.com/llvm/llvm-project/pull/102542