A user program may enumerate sections named with a C identifier using
__start_* and __stop_* symbols. We cannot ICF any such sections because
that could change program semantics.
Differential Revision: https://reviews.llvm.org/D47242
llvm-svn: 333054
Note that this doesn't do the right thing in the case where there is
a linker script. We probably need to move output section assignment
before ICF to get the correct behaviour here.
Differential Revision: https://reviews.llvm.org/D47241
llvm-svn: 333052
The --keep-unique <symbol> option is taken from gold. The intention is that
<symbol> will be prevented from being folded by ICF. Although not
specifically mentioned in the documentation <symbol> only matches
global symbols, with a warning if the symbol is not found.
The implementation finds the Section defining <symbol> and removes it from
the set of sections considered for ICF.
Differential Revision: https://reviews.llvm.org/D46755
llvm-svn: 332332
Summary:
r328610 fixed a data race in the COFF linker. This change makes a
similar fix to the ELF linker.
Reviewers: ruiu, pcc, rnk
Reviewed By: ruiu
Subscribers: emaste, llvm-commits, arichardson
Differential Revision: https://reviews.llvm.org/D45192
llvm-svn: 329088
The Data member of synthetic section's is not valid and empty. The Data
member is required to be valid by ICF as it is used by ICF to determine
the equality of section contents. Therefore, exclude synthetic sections
from ICF.
Fixes bug PR36910.
Differential Revision: https://reviews.llvm.org/D44923
llvm-svn: 328624
Latest patch version now.
Original commit message:
[ELF] - Do not crash with --emit-relocs and --icf=all together.
Previously we would crash because did not mark .rel[a] sections
as dead and they tried to access parent which was not live
after ICF and therefore was null.
Differential revision: https://reviews.llvm.org/D43241
llvm-svn: 325879
GNU gold doesn't print out ICF sections for -verbose. It only shows
them for -print-icf-sections. We printed out them for -verbose because
we didn't have -print-icf-sections. Now that we have the option, there's
no reason to print out for -verbose.
Differential Revision: https://reviews.llvm.org/D43100
llvm-svn: 324755
Previously, multiple chunks of --print-icf-sections messages were interleaved
and didn't make sense. This is because forEachClass is multi-threaded.
llvm-svn: 324683
Currently ICF information is output through stderr if the "--verbose"
flag is used. This differs to Gold for example, which uses an explicit
flag to output this to stdout. This commit adds the
"--print-icf-sections" and "--no-print-icf-sections" flags and changes
the output message format for clarity and consistency with
"--print-gc-sections". These messages are still output to stderr if
using the verbose flag. However to avoid intermingled message output to
console, this will not occur when the "--print-icf-sections" flag is
used.
Existing tests have been modified to expect the new message format from
stderr.
Patch by Owen Reynolds.
Differential Revision: https://reviews.llvm.org/D42375
Reviewers: ruiu, rafael
Reviewed by:
llvm-svn: 323976
When we have --icf=safe we should be able to define --icf=all as a
shorthand for --icf=safe --ignore-function-address-equality.
For now --ignore-function-address-equality is used only to control
access to non preemptable symbols in shared libraries.
llvm-svn: 322152
An internal linker has support for merging identical data and in some
cases it can be a significant win.
This is behind an off by default flag so it has to be requested
explicitly.
llvm-svn: 320448
Now that DefinedRegular is the only remaining derived class of
Defined, we can merge the two classes.
Differential Revision: https://reviews.llvm.org/D39667
llvm-svn: 317448
Now that we have only SymbolBody as the symbol class. So, "SymbolBody"
is a bit strange name now. This is a mechanical change generated by
perl -i -pe s/SymbolBody/Symbol/g $(git grep -l SymbolBody lld/ELF lld/COFF)
nd clang-format-diff.
Differential Revision: https://reviews.llvm.org/D39459
llvm-svn: 317370
Summary:
This will allow using the functionality from other linkers. It is also
a prerequisite for sharing the error logging code.
Reviewers: ruiu
Reviewed By: ruiu
Subscribers: emaste, mgorny, llvm-commits
Differential Revision: https://reviews.llvm.org/D38822
llvm-svn: 315725
Computing section content hashes early seems like a win in terms of
performance. It increases a chance that two different sections will get
different class IDs from the beginning.
Without threads, this patch improves Chromium link time by about 0.3
seconds. With threads, by 0.1 seconds. That's less than 1% time saving
but not bad for a small patch.
llvm-svn: 314644
Relocations referring to merge sections are considered equal if they
resolve to the same offset in the same output section.
Differential Revision: https://reviews.llvm.org/D34094
llvm-svn: 305177
This creates a new library called BinaryFormat that has all of
the headers from llvm/Support containing structure and layout
definitions for various types of binary formats like dwarf, coff,
elf, etc as well as the code for identifying a file from its
magic.
Differential Revision: https://reviews.llvm.org/D33843
llvm-svn: 304864
This is the only place we use threads for ICF. The intention of this code
was to split an input vector into 256 shards and process them in parallel.
What the code was actually doing was to split an input into 257 shards,
process the first 256 shards in parallel, and the remaining one in serial.
That means this code takes ceil(256/n)+1 instead of ceil(256/n) where n
is the number of available CPU cores. The former converges to 2 while
the latter converges to 1.
This patches fixes the above issue.
llvm-svn: 303797
ARM Exception Index Table sections .ARM.exidx have an implicit dependency
on code sections via SHF_LINK_ORDER. When code sections are folded by ICF
we must mark the unique .ARM.exidx table that describes it as not live
to prevent an illegal entry in the exception table.
Note that we do not try and follow the relocations from the .ARM.exidx
section to the .ARM.extab sections to mark these as not live. Leaving
these sections is not a correctness problem. In theory these could be
removed via an application of garbage collection.
Fixes https://bugs.llvm.org/show_bug.cgi?id=32614
Differential Revision: https://reviews.llvm.org/D31932
llvm-svn: 300182
We had a few Config member functions that returns configuration values.
For example, we had is64() which returns true if the target is 64-bit.
The return values of these functions are constant and never change.
This patch is to compute them only once to make it clear that they'll
never change.
llvm-svn: 298168
Previously, LLD merged all read-only sections. So the following
program prints out "true" if -icf=all is specified.
static const int foo = 1;
static const int bar = 1;
int main() { printf("%s\n", &foo == &bar ? "true" : "false"); }
This is somewhat counter-intuitive, and it actually caused nasty issues.
One example is https://bugs.chromium.org/p/chromium/issues/detail?id=682773#c24.
This patch changes the way how it works. Now ICF merges only functions
(i.e. executable sections).
Differential Revision: https://reviews.llvm.org/D30365
llvm-svn: 296534
The list of all input sections was defined in SymbolTable class for a
historical reason. The list itself is not a template. However, because
SymbolTable class is a template, we needed to pass around ELFT to access
the list. This patch moves the list out of the class so that it doesn't
need ELFT.
llvm-svn: 296309
With the current design an InputSection is basically anything that
goes directly in a OutputSection. That includes plain input section
but also synthetic sections, so this should probably not be a
template.
llvm-svn: 295993
If two sections contained relocations to absolute symbols with the same
value we would crash when trying to access their sections. Add a check that
both symbols point to sections before accessing their sections, and treat
absolute symbols as equal if their values are equal.
Differential Revision: https://reviews.llvm.org/D28935
llvm-svn: 292578
I removed a wrong optimization for ICF in r288527. Sean Silva suggested
in a post commit review that the correct algorithm can be implemented
easily. So is this patch.
llvm-svn: 288620
This is a hack for single thread execution. We are using Color[0] and
Color[1] alternately on each iteration. This optimization is to look
at the next slot as opposted to the current slot to get recent results
early. Turns out that the assumption is wrong, because the other slots
are not always have the most recent values, but instead it may have
stale values of the previous iteration. This patch removes that
performance hack.
llvm-svn: 288527
The assertion asserted that colorable sections can never have
a reference to non-colorable sections, but that was simply wrong.
They can have references to non-colorable sections. If that's the
case, referenced sections must be the same in terms of pointer
comparison.
llvm-svn: 288511
r288228 seems to have regressed ICF performance in some cases in which
a lot of sections are actually mergeable. In r288228, I made a change
to create a Range object for each new color group. So every time we
split a group, we allocated and added a new group to a list of groups.
This patch essentially reverted r288228 with an improvement to
parallelize the original algorithm.
Now the ICF main loop is entirely allocation-free and lock-free.
Just like pre-r288228, we search for group boundaries by linear scan
instead of managing the information using Range class. r288228 was
neutral in performance-wise, and so is this patch.
I confirmed that this produces the exact same result as before
using chromium and clang as tests.
llvm-svn: 288480
Peter Collingbourne