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Add warning about CHECK-DAG with variable definition

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192479 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Renato Golin 2013-10-11 18:50:22 +00:00
parent 47cbe033f6
commit f02062f889
1 changed files with 37 additions and 9 deletions
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docs/CommandGuide/FileCheck.rst
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@ -216,6 +216,19 @@ in the natural order:
Bar b;
// CHECK-DAG: @_ZTV3Bar =
``CHECK-NOT:`` directives could be mixed with ``CHECK-DAG:`` directives to
exclude strings between the surrounding ``CHECK-DAG:`` directives. As a result,
the surrounding ``CHECK-DAG:`` directives cannot be reordered, i.e. all
occurrences matching ``CHECK-DAG:`` before ``CHECK-NOT:`` must not fall behind
occurrences matching ``CHECK-DAG:`` after ``CHECK-NOT:``. For example,
.. code-block:: llvm
; CHECK-DAG: BEFORE
; CHECK-NOT: NOT
; CHECK-DAG: AFTER
This case will reject input strings where ``BEFORE`` occurs after ``AFTER``.
With captured variables, ``CHECK-DAG:`` is able to match valid topological
orderings of a DAG with edges from the definition of a variable to its use.
@ -230,19 +243,34 @@ sequences from the instruction scheduler. For example,
In this case, any order of that two ``add`` instructions will be allowed.
``CHECK-NOT:`` directives could be mixed with ``CHECK-DAG:`` directives to
exclude strings between the surrounding ``CHECK-DAG:`` directives. As a result,
the surrounding ``CHECK-DAG:`` directives cannot be reordered, i.e. all
occurrences matching ``CHECK-DAG:`` before ``CHECK-NOT:`` must not fall behind
occurrences matching ``CHECK-DAG:`` after ``CHECK-NOT:``. For example,
If you are defining `and` using variables in the same ``CHECK-DAG:`` block,
be aware that the definition rule can match `after` its use.
So, for instance, the code below will pass:
.. code-block:: llvm
; CHECK-DAG: BEFORE
; CHECK-NOT: NOT
; CHECK-DAG: AFTER
; CHECK-DAG: vmov.32 [[REG2:d[0-9]+]][0]
; CHECK-DAG: vmov.32 [[REG2]][1]
vmov.32 d0[1]
vmov.32 d0[0]
This case will reject input strings where ``BEFORE`` occurs after ``AFTER``.
While this other code, will not:
.. code-block:: llvm
; CHECK-DAG: vmov.32 [[REG2:d[0-9]+]][0]
; CHECK-DAG: vmov.32 [[REG2]][1]
vmov.32 d1[1]
vmov.32 d0[0]
While this can be very useful, it's also dangerous, because in the case of
register sequence, you must have a strong order (read before write, copy before
use, etc). If the definition your test is looking for doesn't match (because
of a bug in the compiler), it may match further away from the use, and mask
real bugs away.
In those cases, to enforce the order, use a non-DAG directive between DAG-blocks.
The "CHECK-LABEL:" directive
~~~~~~~~~~~~~~~~~~~~~~~~~~~~