Add new directive called CHECK-LABEL to FileCheck.

CHECK-LABEL is meant to be used in place on CHECK on lines containing identifiers or other unique labels (they need not actually be labels in the source or output language, though.) This is used to break up the input stream into separate blocks delineated by CHECK-LABEL lines, each of which is checked independently. This greatly improves the accuracy of errors and fix-it hints in many cases, and allows for FileCheck to recover from errors in one block by continuing to subsequent blocks.

Some tests will be converted to use this new directive in forthcoming patches.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186162 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 49 insertions, 0 deletions

diff --git a/docs/CommandGuide/FileCheck.rst b/docs/CommandGuide/FileCheck.rst
index 809eee0469..9d7f63cea9 100644
--- a/docs/CommandGuide/FileCheck.rst
+++ b/docs/CommandGuide/FileCheck.rst
@@ -243,6 +243,55 @@ occurrences matching ``CHECK-DAG:`` after ``CHECK-NOT:``. For example,
 
 This case will reject input strings where ``BEFORE`` occurs after ``AFTER``.
 
+The "CHECK-LABEL:" directive
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Sometimes in a file containing multiple tests divided into logical blocks, one
+or more ``CHECK:`` directives may inadvertently succeed by matching lines in a
+later block. While an error will usually eventually be generated, the check
+flagged as causing the error may not actually bear any relationship to the
+actual source of the problem.
+
+In order to produce better error messages in these cases, the "``CHECK-LABEL:``"
+directive can be used. It is treated identically to a normal ``CHECK``
+directive except that the FileCheck utility makes an additional assumption that
+a line matched by the directive cannot also be matched by any other check
+present in ``match-filename``; this is intended to be used for lines containing
+labels or other unique identifiers. Conceptually, the presence of
+``CHECK-LABEL`` divides the input stream into separate blocks, each of which is
+processed independently, preventing a ``CHECK:`` directive in one block
+matching a line in another block. For example,
+
+.. code-block:: llvm
+
+  define %struct.C* @C_ctor_base(%struct.C* %this, i32 %x) {
+  entry:
+  ; CHECK-LABEL: C_ctor_base:
+  ; CHECK: mov [[SAVETHIS:r[0-9]+]], r0
+  ; CHECK: bl A_ctor_base
+  ; CHECK: mov r0, [[SAVETHIS]]
+    %0 = bitcast %struct.C* %this to %struct.A*
+    %call = tail call %struct.A* @A_ctor_base(%struct.A* %0)
+    %1 = bitcast %struct.C* %this to %struct.B*
+    %call2 = tail call %struct.B* @B_ctor_base(%struct.B* %1, i32 %x)
+    ret %struct.C* %this
+  }
+
+  define %struct.D* @D_ctor_base(%struct.D* %this, i32 %x) {
+  entry:
+  ; CHECK-LABEL: D_ctor_base:
+
+The use of ``CHECK-LABEL:`` directives in this case ensures that the three
+``CHECK:`` directives only accept lines corresponding to the body of the
+``@C_ctor_base`` function, even if the patterns match lines found later in
+the file.
+
+There is no requirement that ``CHECK-LABEL:`` directives contain strings that
+correspond to actual syntactic labels in a source or output language: they must
+simply uniquely match a single line in the file being verified.
+
+``CHECK-LABEL:`` directives cannot contain variable definitions or uses.
+
 FileCheck Pattern Matching Syntax
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~