[PATCH][RFC] Add 'CHECK-<N>' directive in FileCheck

[Michael Liao]

Hi,

As the usage of 'grep' in regression tests is deprecated [1], the
attached patch proposes adding 'CHECK-<N>' to cover one usage of 'grep',
i.e. 'grep <pat> | count <N>' which check there are exactly <N>
occurrences of <pat> in the input string.

Technically, it's possible to do that *without* introducing a new
directive. For example, to verify there are exactly 2 occurrences of
'movmsk' in the input string, a test could be written like this:

; CHECK: movmsk
; CHECK: movmsk
; CHECK-NOT: movmsk

Semantically, it means it will check up to two occurrences of 'movmsk'
and check, after that, there's no occurrence of 'movmsk' till EOF. That
just means there are exactly 2 occurrences of ''movmsk''. But, when <N>
is a large number, 'CHECK-<N>' is much more convenient and explicit to
put the intention to check <N> occurrences. The aforementioned example
could be rewritten as:

; CHECK-2: movmsk
; CHECK-NOT: movmsk

The attached patches have 3 parts:
* 0001-Refactor-string-checking.patch is a code refactoring of the
current check string.
* 0002-Add-CHECK-N-support.patch adds the support of CHECK-<N>. Only one
regression in LLVM is required modifying as it have two check-prefixes,
'X86' and 'X86-64'. With the new notation, the check string prefixed
with the later will be interpreted as 64 occurrences of 'X86' when
checking the former. It's simply changed by replacing 'X86-64' with
'X64'. Document and test cases for 'CHECK-<N>' are added as well.
* 0001-Avoid-conflicting-with-CHECK-N-in-regression-tests.patch revises
clang regression tests to avoid conflicts with 'CHECK-<N>'.

Ofc, a common wise to revise 'check-prefix' may need to avoid conflicts
found so far or we revise 'CHECK-<N>' for the same purpose.

Comments?

Yours
- Michael

--
[1] http://llvm.org/docs/TestingGuide.html
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