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The motivating use case is to support import the function declaration
across modules to construct call graph edges for indirect calls [1]
when importing the function definition costs too much compile time
(e.g., the function is too large has no `noinline` attribute).
1. Currently, when the compiled IR module doesn't have a function
definition but its postlink combined summary contains the function
summary or a global alias summary with this function as aliasee, the
function definition will be imported from source module by IRMover. The
implementation is in FunctionImporter::importFunctions [2]
2. In order for FunctionImporter to import a declaration of a function,
both function summary and alias summary need to carry the def / decl
state. Specifically, all existing summary fields doesn't differ across
import modules, but the def / decl state of is decided by
`<ImportModule, Function>`.
This change encodes the def/decl state in `GlobalValueSummary::GVFlags`.
In the subsequent changes
1. The indexing step `computeImportForModule` [3]
will compute the set of definitions and the set of declarations for each
module, and passing on the information to bitcode writer.
2. Bitcode writer will look up the def/decl state and sets the state
when it writes out the flag value. This is demonstrated in
https://github.com/llvm/llvm-project/pull/87600
3. Function importer will read the def/decl state when reading the
combined summary to figure out two sets of global values, and IRMover
will be updated to import the declaration (aka linkGlobalValuePrototype [4])
into the destination module.
- The next change is https://github.com/llvm/llvm-project/pull/87600
[1] mentioned in rfc https://discourse.llvm.org/t/rfc-for-better-call-graph-sort-build-a-more-complete-call-graph-by-adding-more-indirect-call-edges/74029#support-cross-module-function-declaration-import-5
[2] https://github.com/llvm/llvm-project/blob/3b337242ee165554f0017b00671381ec5b1ba855/llvm/lib/Transforms/IPO/FunctionImport.cpp#L1608-L1764
[3] https://github.com/llvm/llvm-project/blob/3b337242ee165554f0017b00671381ec5b1ba855/llvm/lib/Transforms/IPO/FunctionImport.cpp#L856
[4] https://github.com/llvm/llvm-project/blob/3b337242ee165554f0017b00671381ec5b1ba855/llvm/lib/Linker/IRMover.cpp#L605
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This adds support for a HasTailCall flag on function call edges in the
ThinLTO summary. It is intended for use in aiding discovery of missing
frames from tail calls in profiled call stacks for MemProf of profiled
binaries that did not disable tail call elimination. A follow on change
will add the use of this new flag during MemProf context disambiguation.
The new flag is encoded in the bitcode along with either the hotness
flag from the profile, or the relative block frequency under the
-write-relbf-to-summary flag when there is no profile data.
Because we now will always have some additional call edge information, I
have removed the non-profile function summary record format, and we
simply encode the tail call flag along with a hotness type of none when
there is no profile information or relative block frequency. The change
of record format and name caused most of the test case changes.
I have added explicit testing of generation of the new tail call flag
into the bitcode and IR assembly format as part of the changes to
llvm/test/Bitcode/thinlto-function-summary-refgraph.ll. I have also
added round trip testing through assembly and bitcode to
llvm/test/Assembler/thinlto-summary.ll.
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Differential Revision: https://reviews.llvm.org/D115492
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Thinlink provides an opportunity to propagate function attributes across modules, enabling additional propagation opportunities.
This change propagates (currently default off, turn on with `disable-thinlto-funcattrs=1`) noRecurse and noUnwind based off of function summaries of the prevailing functions in bottom-up call-graph order. Testing on clang self-build:
1. There's a 35-40% increase in noUnwind functions due to the additional propagation opportunities.
2. Throughput is measured at 10-15% increase in thinlink time which itself is 1.5% of E2E link time.
Implementation-wise this adds the following summary function attributes:
1. noUnwind: function is noUnwind
2. mayThrow: function contains a non-call instruction that `Instruction::mayThrow` returns true on (e.g. windows SEH instructions)
3. hasUnknownCall: function contains calls that don't make it into the summary call-graph thus should not be propagated from (e.g. indirect for now, could add no-opt functions as well)
Testing:
Clang self-build passes and 2nd stage build passes check-all
ninja check-all with newly added tests passing
Reviewed By: tejohnson
Differential Revision: https://reviews.llvm.org/D36850
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Imported functions and variable get the visibility from the module supplying the
definition. However, non-imported definitions do not get the visibility from
(ELF) the most constraining visibility among all modules (Mach-O) the visibility
of the prevailing definition.
This patch
* adds visibility bits to GlobalValueSummary::GVFlags
* computes the result visibility and propagates it to all definitions
Protected/hidden can imply dso_local which can enable some optimizations (this
is stronger than GVFlags::DSOLocal because the implied dso_local can be
leveraged for ELF -shared while default visibility dso_local has to be cleared
for ELF -shared).
Note: we don't have summaries for declarations, so for ELF if a declaration has
the most constraining visibility, the result visibility may not be that one.
Differential Revision: https://reviews.llvm.org/D92900
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This patch imports constant variables even when they can't be internalized
(which results in promotion). This offers some extra constant folding
opportunities.
Differential revision: https://reviews.llvm.org/D70404
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llvm-svn: 365215
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llvm-svn: 365206
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It's possible that some function can load and store the same
variable using the same constant expression:
store %Derived* @foo, %Derived** bitcast (%Base** @bar to %Derived**)
%42 = load %Derived*, %Derived** bitcast (%Base** @bar to %Derived**)
The bitcast expression was mistakenly cached while processing loads,
and never examined later when processing store. This caused @bar to
be mistakenly treated as read-only variable. See load-store-caching.ll.
llvm-svn: 365188
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This reverts r365040 (git commit 5cacb914758c7f436b47c8362100f10cef14bbc4)
Speculatively reverting, since this appears to have broken check-lld on
Linux. Partial analysis in https://crbug.com/981168.
llvm-svn: 365097
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Differential revision: https://reviews.llvm.org/D63444
llvm-svn: 365040
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Summary:
We hit undefined references building with ThinLTO when one source file
contained explicit instantiations of a template method (weak_odr) but
there were also implicit instantiations in another file (linkonce_odr),
and the latter was the prevailing copy. In this case the symbol was
marked hidden when the prevailing linkonce_odr copy was promoted to
weak_odr. It led to unsats when the resulting shared library was linked
with other code that contained a reference (expecting to be resolved due
to the explicit instantiation).
Add a CanAutoHide flag to the GV summary to allow the thin link to
identify when all copies are eligible for auto-hiding (because they were
all originally linkonce_odr global unnamed addr), and only do the
auto-hide in that case.
Most of the changes here are due to plumbing the new flag through the
bitcode and llvm assembly, and resulting test changes. I augmented the
existing auto-hide test to check for this situation.
Reviewers: pcc
Subscribers: mehdi_amini, inglorion, eraman, dexonsmith, arphaman, dang, llvm-commits, steven_wu, wmi
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D59709
llvm-svn: 360466
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Differential revision: https://reviews.llvm.org/D54754
llvm-svn: 347489
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An attempt to recommit r346584 after failure on OSX build bot.
Fixed cache key computation in ThinLTOCodeGenerator and added
test case
llvm-svn: 347033
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This reverts commit 10c84a8f35cae4a9fc421648d9608fccda3925f2.
llvm-svn: 346768
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This patch allows internalising globals if all accesses to them
(from live functions) are from non-volatile load instructions
Differential revision: https://reviews.llvm.org/D49362
llvm-svn: 346584
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Summary:
Adds assembly parsing support for the module summary index (follow on
to r333335 which added the assembly writing support).
I added support to llvm-as to invoke the index parsing, so that it can
create either a bitcode file with a Module and a per-module index, or
a combined index without a Module.
I will send follow on patches soon to do the following:
- add support to tools such as llvm-lto2 to parse the per-module indexes
from assembly instead of bitcode when testing the thin link.
- verification support.
Depends on D47844 and D47842.
Reviewers: pcc, dexonsmith, mehdi_amini
Subscribers: inglorion, eraman, steven_wu, llvm-commits
Differential Revision: https://reviews.llvm.org/D47905
llvm-svn: 335602
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Fix a few more bot failures due to r333335:
- don't match path other than file name, since the delimiter is
different for Windows
- The summary IDs in thinlto-function-summary-refgraph.ll may vary
and therefore can't be matched exactly, because the ordering depends
on the iteration order of the index map which is keyed by GUID. The GUID
for private values will depend on the path.
llvm-svn: 333338
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Don't try to match the exact GUID for private symbols, as the
hashed name includes the file path.
llvm-svn: 333337
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Summary:
Implements AsmWriter support for printing the module summary index to
assembly with the format discussed in the RFC "LLVM Assembly format for
ThinLTO Summary".
Implements just enough of the parsing support to recognize and ignore
the summary entries. As agreed in the RFC thread, this will be the
behavior when assembling the IR. A follow on change will implement
parsing/assembling of the summary entries for use by tools that
currently build the summary index from bitcode.
Reviewers: dexonsmith, pcc
Subscribers: inglorion, eraman, steven_wu, dblaikie, llvm-commits
Differential Revision: https://reviews.llvm.org/D46699
llvm-svn: 333335
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While updating clang tests for having clang set dso_local I noticed
that:
- There are *a lot* of tests to update.
- Many of the updates are redundant.
They are redundant because a GV is "obviously dso_local". This patch
starts formalizing that a bit by requiring that internal and private
GVs be dso_local too. Since they all are, we don't have to print
dso_local to the textual representation, making it a bit more compact
and easier to read.
llvm-svn: 322317
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Adds function attributes to index: ReadNone, ReadOnly, NoRecurse, NoAlias. This attributes will be used for future ThinLTO optimizations that will propagate function attributes across modules.
llvm-svn: 310061
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Differential Revision: https://reviews.llvm.org/D33973
llvm-svn: 306487
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Add a top-level STRTAB block containing a string table blob, and start storing
strings for module codes FUNCTION, GLOBALVAR, ALIAS, IFUNC and COMDAT in
the string table.
This change allows us to share names between globals and comdats as well
as between modules, and improves the efficiency of loading bitcode files by
no longer using a bit encoding for symbol names. Once we start writing the
irsymtab to the bitcode file we will also be able to share strings between
it and the module.
On my machine, link time for Chromium for Linux with ThinLTO decreases by
about 7% for no-op incremental builds or about 1% for full builds. Total
bitcode file size decreases by about 3%.
As discussed on llvm-dev:
http://lists.llvm.org/pipermail/llvm-dev/2017-April/111732.html
Differential Revision: https://reviews.llvm.org/D31838
llvm-svn: 300464
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Summary:
This patch improves thinlto importer
by importing 3x larger functions that are called from hot block.
I compared performance with the trunk on spec, and there
were about 2% on povray and 3.33% on milc. These results seems
to be consistant and match the results Teresa got with her simple
heuristic. Some benchmarks got slower but I think they are just
noisy (mcf, xalancbmki, omnetpp)- running the benchmarks again with
more iterations to confirm. Geomean of all benchmarks including the noisy ones
were about +0.02%.
I see much better improvement on google branch with Easwaran patch
for pgo callsite inlining (the inliner actually inline those big functions)
Over all I see +0.5% improvement, and I get +8.65% on povray.
So I guess we will see much bigger change when Easwaran patch will land
(it depends on new pass manager), but it is still worth putting this to trunk
before it.
Implementation details changes:
- Removed CallsiteCount.
- ProfileCount got replaced by Hotness
- hot-import-multiplier is set to 3.0 for now,
didn't have time to tune it up, but I see that we get most of the interesting
functions with 3, so there is no much performance difference with higher, and
binary size doesn't grow as much as with 10.0.
Reviewers: eraman, mehdi_amini, tejohnson
Subscribers: mehdi_amini, llvm-commits
Differential Revision: https://reviews.llvm.org/D24638
llvm-svn: 282437
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Right now it only contains the LinkageType, but will be extended
with "hasSection", "isOptSize", "hasInlineAssembly", etc.
Differential Revision: http://reviews.llvm.org/D19404
From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 267319
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Summary:
Let keep llvm-as "dumb": it converts textual IR to bitcode. This
commit removes the dependency from llvm-as to libLLVMAnalysis.
We'll add back summary in llvm-as if we get to a textual
representation for it at some point. In the meantime, opt seems
like a better place for that.
Reviewers: tejohnson
Subscribers: joker.eph, llvm-commits
Differential Revision: http://reviews.llvm.org/D19032
From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 266131
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(Resubmitting after fixing missing file issue)
With the changes in r263275, there are now more than just functions in
the summary. Completed the renaming of data structures (started in
r263275) to reflect the wider scope. In particular, changed the
FunctionIndex* data structures to ModuleIndex*, and renamed related
variables and comments. Also renamed the files to reflect the changes.
A companion clang patch will immediately succeed this patch to reflect
this renaming.
llvm-svn: 263513
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This reverts commit r263490. Missed a file.
llvm-svn: 263493
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With the changes in r263275, there are now more than just functions in
the summary. Completed the renaming of data structures (started in
r263275) to reflect the wider scope. In particular, changed the
FunctionIndex* data structures to ModuleIndex*, and renamed related
variables and comments. Also renamed the files to reflect the changes.
A companion clang patch will immediately succeed this patch to reflect
this renaming.
llvm-svn: 263490
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Summary:
This patch adds support for including a full reference graph including
call graph edges and other GV references in the summary.
The reference graph edges can be used to make importing decisions
without materializing any source modules, can be used in the plugin
to make file staging decisions for distributed build systems, and is
expected to have other uses.
The call graph edges are recorded in each function summary in the
bitcode via a list of <CalleeValueIds, StaticCount> tuples when no PGO
data exists, or <CalleeValueId, StaticCount, ProfileCount> pairs when
there is PGO, where the ValueId can be mapped to the function GUID via
the ValueSymbolTable. In the function index in memory, the call graph
edges reference the target via the CalleeGUID instead of the
CalleeValueId.
The reference graph edges are recorded in each summary record with a
list of referenced value IDs, which can be mapped to value GUID via the
ValueSymbolTable.
Addtionally, a new summary record type is added to record references
from global variable initializers. A number of bitcode records and data
structures have been renamed to reflect the newly expanded scope of the
summary beyond functions. More cleanup will follow.
Reviewers: joker.eph, davidxl
Subscribers: joker.eph, llvm-commits
Differential Revision: http://reviews.llvm.org/D17212
llvm-svn: 263275
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