[PATCH] D48986: [FileCheck] Fix search ranges for DAG-NOT-DAG

[Joel E. Denny via Phabricator via llvm-commits]

jdenny created this revision.
jdenny added a reviewer: probinson.

A DAG-NOT-DAG is a CHECK-DAG group, X, followed by a CHECK-NOT group,
N, followed by a CHECK-DAG group, Y.  Let y be the initial directive
of Y.  This patch makes the following changes to the behavior:

1. Directives in N can no longer match within part of Y's match range just because y happens not to be the earliest match from Y.  Specifically, this patch withdraws N's search range end from y's match range start to Y's match range start.
2. y can no longer match within X's match range, where a y match produced a reordering complaint, which is thus no longer possible.  Specifically, this patch withdraws y's search range start from X's permitted range start to X's match range end, which was already the search range start for other members of Y.

Both of these changes can only increase the number of test passes: #1
constrains the ability of CHECK-NOTs to match, and #2 expands the 
ability of CHECK-DAGs to match without complaints.

This changes are based on discussions at:

  <http://lists.llvm.org/pipermail/llvm-dev/2018-May/123550.html>
  <https://reviews.llvm.org/D47106>

which conclude that:

1. These changes simplify the FileCheck conceptual model.  First, it makes search ranges for DAG-NOT-DAG more consistent with other cases.  Second, it was confusing that y was treated differently from the rest of Y.
2. These changes add theoretical use cases for DAG-NOT-DAG that had no obvious means to be expressed otherwise.  We can justify the first half of this assertion with the observation that these changes can only increase the number of test passes.
3. Reordering detection for DAG-NOT-DAG had no obvious real benefit.

We don't have evidence from real uses cases to help us debate
conclusions #2 and #3, but #1 at least seems intuitive.


Repository:
  rL LLVM

https://reviews.llvm.org/D48986

Files:
  test/FileCheck/check-dag-not-dag.txt
  test/FileCheck/check-dag-overlap.txt
  utils/FileCheck/FileCheck.cpp

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