[Utils] Deal with occasionally deleted functions

[jdoerfert]

Summary

When functions exist for some but not all run lines we need to be
careful when selecting the prefix. So far, a common prefix was
potentially chosen as there was never a "conflict" that would have
caused otherwise. With this patch we avoid common prefixes if they
are used by run lines that do not emit the function.

Tested as part of D68766 and the follow up that adds the Attributor test
lines to all argument promotion tests.

[jdoerfert]

The difference is when we run update_test_checks.py on the following code

; RUN: opt -S < %s | FileCheck %s --check-prefixes=ALL,FIRST
; RUN: opt -S -globalopt < %s | FileCheck %s --check-prefixes=ALL,SECOND

define internal void @f() {
  ret void
}

we will see

; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S < %s | FileCheck %s --check-prefixes=ALL,FIRST
; RUN: opt -S -globalopt < %s | FileCheck %s --check-prefixes=ALL,SECOND

define internal void @f() {
; FIRST-LABEL: define {{[^@]+}}@f(
; FIRST-NEXT:    ret void
;
  ret void
}

and not

; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S < %s | FileCheck %s --check-prefixes=ALL,FIRST
; RUN: opt -S -globalopt < %s | FileCheck %s --check-prefixes=ALL,SECOND

define internal void @f() {
; ALL-LABEL: @f(
; ALL-NEXT:    ret void
;
  ret void
}

---

ping

[lebedev.ri]

Now that i believe there's some testing infra for these utils, add/update tests for this?

[jdoerfert]

Add a regression test

[merge_guards_bot]

Unit tests: unknown.

clang-tidy: unknown.

clang-format: unknown.

Build artifacts: diff.json, console-log.txt

[lebedev.ri]

llvm/utils/UpdateTestChecks/common.py

269

I'm having a hard time figuring out whether this blacklist is per-function or global.
I.e. what happens if sometimes_deleted_function.ll has a second function,
that *does* exist for all check prefixes. Will it also only be checked in FIRST check prefix?

[jdoerfert]

Make the test more expressive

[jdoerfert]

llvm/utils/UpdateTestChecks/common.py

269

It's a *per function* blacklist. I updated the test to show that ALL is used for a function that is always present.

[lebedev.ri]

Really convoluted, but seems to be okay.

llvm/utils/UpdateTestChecks/common.py

269

Name is too generic, should maybe be prefix_blacklist.

[merge_guards_bot]

Unit tests: fail. 61156 tests passed, 1 failed and 728 were skipped.

failed: libc++.std/thread/thread_mutex/thread_mutex_requirements/thread_sharedtimedmutex_requirements/thread_sharedtimedmutex_class/try_lock.pass.cpp

clang-tidy: pass.

clang-format: pass.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml