maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

LangRef: Document the allowed metadata dropping transforms. 

Document the current practice regarding dropping metadata on modules,
functions and global variables.

Differential Revision: https://reviews.llvm.org/D29110

llvm-svn: 293101
This commit is contained in:
Peter Collingbourne 2017-01-25 21:50:14 +00:00
parent bfe02642da
commit 7b5b7c7444
1 changed files with 16 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
llvm/docs/LangRef.rst
View File

@ -3941,15 +3941,28 @@ to the ``add`` instruction using the ``!dbg`` identifier:
%indvar.next = add i64 %indvar, 1, !dbg !21
Metadata can also be attached to a function definition. Here metadata ``!22``
is attached to the ``foo`` function using the ``!dbg`` identifier:
Metadata can also be attached to a function or a global variable. Here metadata
``!22`` is attached to the ``f1`` and ``f2 functions, and the globals ``g1``
and ``g2`` using the ``!dbg`` identifier:
.. code-block:: llvm
define void @foo() !dbg !22 {
declare !dbg !22 void @f1()
define void @f2() !dbg !22 {
ret void
}
@g1 = global i32 0, !dbg !22
@g2 = external global i32, !dbg !22
A transformation is required to drop any metadata attachment that it does not
know or know it can't preserve. Currently there is an exception for metadata
attachment to globals for ``!type`` and ``!absolute_symbol`` which can't be
unconditionally dropped unless the global is itself deleted.
Metadata attached to a module using named metadata may not be dropped, with
the exception of debug metadata (named metadata with the name ``!llvm.dbg.*``).
More information about specific metadata nodes recognized by the
optimizers and code generator is found below.