Port https://reviews.llvm.org/D117354 from the MachO port.
If both --symbol-ordering-file and call graph profile are present, the
--symbol-ordering-file takes precedence, but the call graph profile is
still used for symbols that don't appear in the order file.
In addition, call graph profile described sections are now ordered
before other sections.
It seems that some functions (.text.unlikely.xxx) may have zero size,
which
makes some builds with enabled assertions fail. Removing the assertion
and
extending one test to fix the build.
The sorting can process such zero-sized functions so no changes there
are needed
We are brining a new algorithm for function layout (reordering) based on the
call graph (extracted from a profile data). The algorithm is an improvement of
top of a known heuristic, C^3. It tries to co-locate hot and frequently executed
together functions in the resulting ordering. Unlike C^3, it explores a larger
search space and have an objective closely tied to the performance of
instruction and i-TLB caches. Hence, the name CDS = Cache-Directed Sort.
The algorithm can be used at the linking or post-linking (e.g., BOLT) stage.
Refer to https://reviews.llvm.org/D152834 for the actual implementation of the
reordering algorithm.
This diff adds a linker option to replace the existing C^3 heuristic with CDS.
The new behavior can be turned on by passing "--use-cache-directed-sort".
(the plan is to make it default in a next diff)
**Perf-impact**
clang-10 binary (built with LTO+AutoFDO/CSSPGO): wins on top of C^3 in [0.3%..0.8%]
rocksDB-8 binary (built with LTO+CSSPGO): wins on top of C^3 in [0.8%..1.5%]
Note that function layout affects the perf the most on older machines (with
smaller instruction/iTLB caches) and when huge pages are not enabled. The impact
on newer processors with huge pages enabled is likely neutral/minor.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D152840
It is fairly easy to forget SectionBase::repl after ICF.
Let ICF rewrite a Defined symbol's `section` field to avoid references to
SectionBase::repl in subsequent passes. This slightly improves the --icf=none
performance due to less indirection (maybe for --icf={safe,all} as well if most
symbols are Defined).
With this change, there is only one reference to `repl` (--gdb-index D89751).
We can undo f4fb5fd7523f8e3c3b3966d43c0a28457b59d1d8 (`Move Repl to SectionBase.`)
but move `repl` to `InputSection` instead.
Reviewed By: ikudrin
Differential Revision: https://reviews.llvm.org/D116093
This makes it clear `ELF/**/*.cpp` files define things in the `lld::elf`
namespace and simplifies `elf::foo` to `foo`.
Reviewed By: atanasyan, grimar, ruiu
Differential Revision: https://reviews.llvm.org/D68323
llvm-svn: 373885
Before, SecToClusters[*] was used to track the belonged cluster.
During a merge (From -> Into), every element of From has to be updated.
Use a union-find set to speed up this use case.
Also, replace `std::vector<int> Sections;` with a doubly-linked
pointers: int Next, Prev;
Reviewed By: Bigcheese
Differential Revision: https://reviews.llvm.org/D46228
llvm-svn: 373708
This patch is mechanically generated by clang-llvm-rename tool that I wrote
using Clang Refactoring Engine just for creating this patch. You can see the
source code of the tool at https://reviews.llvm.org/D64123. There's no manual
post-processing; you can generate the same patch by re-running the tool against
lld's code base.
Here is the main discussion thread to change the LLVM coding style:
https://lists.llvm.org/pipermail/llvm-dev/2019-February/130083.html
In the discussion thread, I proposed we use lld as a testbed for variable
naming scheme change, and this patch does that.
I chose to rename variables so that they are in camelCase, just because that
is a minimal change to make variables to start with a lowercase letter.
Note to downstream patch maintainers: if you are maintaining a downstream lld
repo, just rebasing ahead of this commit would cause massive merge conflicts
because this patch essentially changes every line in the lld subdirectory. But
there's a remedy.
clang-llvm-rename tool is a batch tool, so you can rename variables in your
downstream repo with the tool. Given that, here is how to rebase your repo to
a commit after the mass renaming:
1. rebase to the commit just before the mass variable renaming,
2. apply the tool to your downstream repo to mass-rename variables locally, and
3. rebase again to the head.
Most changes made by the tool should be identical for a downstream repo and
for the head, so at the step 3, almost all changes should be merged and
disappear. I'd expect that there would be some lines that you need to merge by
hand, but that shouldn't be too many.
Differential Revision: https://reviews.llvm.org/D64121
llvm-svn: 365595
Make some small adjustment while touching the code: make parameters
const, use less_first(), etc.
Differential Revision: https://reviews.llvm.org/D60989
llvm-svn: 358943
Patch by Tiancong Wang.
In D36351, Call-Chain Clustering (C3) heuristic is implemented with
option --call-graph-ordering-file <file>.
This patch adds a flag --print-symbol-order=<file> to LLD, and when
specified, it prints out the symbols ordered by the heuristics to the
file. The symbols printout is helpful to those who want to understand
the heuristics and want to reproduce the ordering with
--symbol-ordering-file in later pass.
Differential Revision: https://reviews.llvm.org/D59311
llvm-svn: 357133
to reflect the new license.
We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.
Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.
llvm-svn: 351636
Looking at the current implementation and algorithm description,
it does not seem we need to keep vector with all edges for
each cluster and can just remember the best one. This is NFC change.
Differential revision: https://reviews.llvm.org/D50609
llvm-svn: 340806
It turns out we should not use the std::sort anymore.
r327219 added a new wrapper llvm::sort (D39245).
When EXPENSIVE_CHECKS is defined, it shuffles the
input container and that helps to find non-deterministic
ordering.
Patch changes code to use llvm::sort and std::stable_sort
instead of std::sort
Differential revision: https://reviews.llvm.org/D45969
llvm-svn: 330702
