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Differential D106304

[LangRef] Clarify support for multiple metadata attachments with same id
ClosedPublic

Authored by tejohnson on Jul 19 2021, 12:54 PM.

Details

Reviewers
dexonsmith
Commits
rG54c8902f0236: [LangRef] Clarify support for multiple metadata attachments with same id
Summary

As discussed on D105251, currently the compiler does not support
multiple metadata attachments on instructions having the same
identifier, whereas it does for global objects. Note this in the
Language Reference manual for clarity.

See D105251 for discussions of history behind this divergence, and the
complexities and possible approaches of adding this support to
instructions in the future.

Diff Detail

Unit TestsFailed

TimeTest
2,870 msx64 debian > libarcher.barrier::barrier.c
2,650 msx64 debian > libarcher.critical::critical.c
2,810 msx64 debian > libarcher.critical::lock-nested.c
2,550 msx64 debian > libarcher.critical::lock.c
2,700 msx64 debian > libarcher.parallel::parallel-simple.c
View Full Test Results (19 Failed)

Event Timeline

tejohnson created this revision.Jul 19 2021, 12:54 PM
Herald added a subscriber: jdoerfert. · View Herald TranscriptJul 19 2021, 12:54 PM
tejohnson requested review of this revision.Jul 19 2021, 12:54 PM
Herald added a project: Restricted Project. · View Herald TranscriptJul 19 2021, 12:54 PM
tejohnson mentioned this in D105251: [IR] Allow multiple instruction metadata attachments with same type.Jul 19 2021, 12:54 PM
dexonsmith accepted this revision.Jul 19 2021, 1:08 PM

LGTM; thanks!

This revision is now accepted and ready to land.Jul 19 2021, 1:08 PM
This revision was landed with ongoing or failed builds.Jul 19 2021, 1:19 PM
Closed by commit rG54c8902f0236: [LangRef] Clarify support for multiple metadata attachments with same id (authored by tejohnson). · Explain Why
This revision was automatically updated to reflect the committed changes.
tejohnson added a commit: rG54c8902f0236: [LangRef] Clarify support for multiple metadata attachments with same id.
Harbormaster completed remote builds in B114929: Diff 359886.Jul 19 2021, 1:47 PM

Revision Contents

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Diff 359886

llvm/docs/LangRef.rst

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will use the one that corresponds to the line of the asm that the error will use the one that corresponds to the line of the asm that the error
occurs on. occurs on.
.. _metadata: .. _metadata:
Metadata Metadata
======== ========
LLVM IR allows metadata to be attached to instructions in the program LLVM IR allows metadata to be attached to instructions and global objects in the
that can convey extra information about the code to the optimizers and program that can convey extra information about the code to the optimizers and
code generator. One example application of metadata is source-level code generator. One example application of metadata is source-level
debug information. There are two metadata primitives: strings and nodes. debug information. There are two metadata primitives: strings and nodes.
Metadata does not have a type, and is not a value. If referenced from a Metadata does not have a type, and is not a value. If referenced from a
``call`` instruction, it uses the ``metadata`` type. ``call`` instruction, it uses the ``metadata`` type.
All metadata are identified in syntax by an exclamation point ('``!``'). All metadata are identified in syntax by an exclamation point ('``!``').
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Metadata can be attached to an instruction. Here metadata ``!21`` is attached Metadata can be attached to an instruction. Here metadata ``!21`` is attached
to the ``add`` instruction using the ``!dbg`` identifier: to the ``add`` instruction using the ``!dbg`` identifier:
.. code-block:: llvm .. code-block:: llvm
%indvar.next = add i64 %indvar, 1, !dbg !21 %indvar.next = add i64 %indvar, 1, !dbg !21
Instructions may not have multiple metadata attachments with the same
identifier.
Metadata can also be attached to a function or a global variable. Here metadata 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`` ``!22`` is attached to the ``f1`` and ``f2`` functions, and the globals ``g1``
and ``g2`` using the ``!dbg`` identifier: and ``g2`` using the ``!dbg`` identifier:
.. code-block:: llvm .. code-block:: llvm
declare !dbg !22 void @f1() declare !dbg !22 void @f1()
define void @f2() !dbg !22 { define void @f2() !dbg !22 {
ret void ret void
} }
@g1 = global i32 0, !dbg !22 @g1 = global i32 0, !dbg !22
@g2 = external global i32, !dbg !22 @g2 = external global i32, !dbg !22
Unlike instructions, global objects (functions and global variables) may have
multiple metadata attachments with the same identifier.
A transformation is required to drop any metadata attachment that it does not 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 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 attachment to globals for ``!type`` and ``!absolute_symbol`` which can't be
unconditionally dropped unless the global is itself deleted. unconditionally dropped unless the global is itself deleted.
Metadata attached to a module using named metadata may not be dropped, with 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.*``). the exception of debug metadata (named metadata with the name ``!llvm.dbg.*``).
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