The problem here is the infamous one direction known safe. I was
hesitant to turn it off before b/c of the potential for regressions
without an actual bug from users hitting the problem. This is that bug ;
).
The main performance impact of having known safe in both directions is
that often times it is very difficult to find two releases without a use
in-between them since we are so conservative with determining potential
uses. The one direction known safe gets around that problem by taking
advantage of many situations where we have two retains in a row,
allowing us to avoid that problem. That being said, the one direction
known safe is unsafe. Consider the following situation:
retain(x)
retain(x)
call(x)
call(x)
release(x)
Then we know the following about the reference count of x:
// rc(x) == N (for some N).
retain(x)
// rc(x) == N+1
retain(x)
// rc(x) == N+2
call A(x)
call B(x)
// rc(x) >= 1 (since we can not release a deallocated pointer).
release(x)
// rc(x) >= 0
That is all the information that we can know statically. That means that
we know that A(x), B(x) together can release (x) at most N+1 times. Lets
say that we remove the inner retain, release pair.
// rc(x) == N (for some N).
retain(x)
// rc(x) == N+1
call A(x)
call B(x)
// rc(x) >= 1
release(x)
// rc(x) >= 0
We knew before that A(x), B(x) could release x up to N+1 times meaning
that rc(x) may be zero at the release(x). That is not safe. On the other
hand, consider the following situation where we have a must use of
release(x) that x must be kept alive for after the release(x)**. Then we
know that:
// rc(x) == N (for some N).
retain(x)
// rc(x) == N+1
retain(x)
// rc(x) == N+2
call A(x)
call B(x)
// rc(x) >= 2 (since we know that we are going to release x and that that release can not be the last use of x).
release(x)
// rc(x) >= 1 (since we can not deallocate the pointer since we have a must use after x).
…
// rc(x) >= 1
use(x)
Thus we know that statically the calls to A(x), B(x) can together only
release rc(x) N times. Thus if we remove the inner retain, release pair:
// rc(x) == N (for some N).
retain(x)
// rc(x) == N+1
call A(x)
call B(x)
// rc(x) >= 1
…
// rc(x) >= 1
use(x)
We are still safe unless in the final … there are unbalanced retains,
releases which would have caused the program to blow up anyways even
before optimization occurred. The simplest form of must use is an
additional release that has not been paired up with any retain (if we
had paired the release with a retain and removed it we would not have
the additional use). This fits nicely into the ARC framework since
basically what you do is say that given any nested releases regardless
of what is in between, the inner release is known safe. This enables us to get
back the lost performance.
<rdar://problem/19023795>
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232351 91177308-0d34-0410-b5e6-96231b3b80d8
This will be tested in the next commit (which required it). The commit
is going to update a bunch of tests at the same time.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232350 91177308-0d34-0410-b5e6-96231b3b80d8
This code was casting regions of a memory buffer to a couple of
different structs. This is wrong in a few ways:
1. It breaks aliasing rules.
2. If the buffer isn't aligned, it hits undefined behaviour.
3. It completely ignores endianness differences.
4. The structs being defined for this aren't specifying their padding
properly, so this doesn't even represent the data properly on some
platforms.
This commit is mostly NFC, except that it fixes reading coverage for
32 bit binaries as a side effect of getting rid of the mispadded
structs. I've included a test for that.
I've also baked in that we only handle little endian more explicitly,
since that was true in practice already. I'll fix this to handle
endianness properly in a followup commit.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232346 91177308-0d34-0410-b5e6-96231b3b80d8
The information gathering part of the patch stores a bit more information
than what is strictly necessary for these 2 sections. The rest will
become useful when we start emitting __apple_* type accelerator tables.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232342 91177308-0d34-0410-b5e6-96231b3b80d8
Also, after looking at the raw_svector_stream internals, increase the
size of the SmallString used with it to prevent heap allocation.
Issue found by the Asan bot.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232335 91177308-0d34-0410-b5e6-96231b3b80d8
After much bike shed discussions, we seem to agree to a few loose
but relevant guidelines on how to prepare a commit message. It also
points the attribution section to the new commit messages section
to deduplicate information.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232334 91177308-0d34-0410-b5e6-96231b3b80d8
This code comes with a lot of cruft that is meant to mimic darwin's
dsymutil behavior. A much simpler approach (described in the numerous
FIXMEs that I put in there) gives the right output for the vast
majority of cases. The extra corner cases that are handled differently
need to be investigated: they seem to correctly handle debug info that
is in the input, but that info looks suspicious in the first place.
Anyway, the current code needs to handle this, but I plan to revisit it
as soon as the big round of validation against the classic dsymutil is
over.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232333 91177308-0d34-0410-b5e6-96231b3b80d8
No need to emit a DW_LNS_advance_pc with a 0 increment. Found out while
comparing dsymutil's and LLVM's line table encoding. Not a correctenss
fix, just a small encoding size optimization.
I'm not sure how to generate a sequence that triggers this, and moreover
llvm-dwardump doesn't dump the line table program, thus the effort
involved in creating a testcase for this trivial patch seemed out of
proportion.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232332 91177308-0d34-0410-b5e6-96231b3b80d8
This simplifies code quite a bit and brings the iterators closer to
C++'s iterator concept. No functional change intended.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232319 91177308-0d34-0410-b5e6-96231b3b80d8
Use an overload instead of a default argument for `Metadata::dump()`.
The latter seems to require calling `dump(nullptr)` explicitly when
using a debugger, where as the former doesn't.
Other than utility for debugging, there's NFC here.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232315 91177308-0d34-0410-b5e6-96231b3b80d8
The C++ standard reserves all identifiers starting with an underscore
followed by an uppercase letter for the implementation for any use.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232302 91177308-0d34-0410-b5e6-96231b3b80d8
llvm-vtabledump has grown enough functionality not related to vtables
that it deserves a name which is more descriptive.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232301 91177308-0d34-0410-b5e6-96231b3b80d8
The debug map embedded by ld64 in binaries conatins function sizes.
These sizes are less precise than the ones given by the debug information
(byte granularity vs linker atom granularity), but they might cover code
that is referenced in the line table but not in the DIE tree (that might
very well be a compiler bug that I need to investigate later).
Anyway, extracting that information is necessary to be able to mimic
dsymutil's behavior exactly.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232300 91177308-0d34-0410-b5e6-96231b3b80d8
Change accessors to downcast to `MDLocalVariable` and `MDExpression`,
now that we have -verify checks in place to confirm that it's safe.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232299 91177308-0d34-0410-b5e6-96231b3b80d8
Verify that debug info intrinsic arguments are valid. (These checks
will not recurse through the full debug info graph, so they don't need
to be cordoned of in `DebugInfoVerifier`.)
With those checks in place, changing the `DbgIntrinsicInst` accessors to
downcast to `MDLocalVariable` and `MDExpression` is natural (added isa
specializations in `Metadata.h` to support this).
Added tests to `test/Verifier` for the new -verify checks, and fixed the
debug info in all the in-tree tests.
If you have out-of-tree testcases that have started to fail to -verify,
hopefully the verify checks are helpful. The most likely problem is
that the expression argument is `!{}` (instead of `!MDExpression()`).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232296 91177308-0d34-0410-b5e6-96231b3b80d8
This is already assumed to be non-null above due to a dyn_cast<>. Also
remove extraneous braces around statement.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232292 91177308-0d34-0410-b5e6-96231b3b80d8
This test for function-local metadata did strange things, and never
really sent in valid arguments for `llvm.dbg.declare` and
`llvm.dbg.value` intrinsics. Those that might have once been valid have
bitrotted.
Rewrite it to be a targeted test for function-local metadata --
unrelated to debug info, which is tested elsewhere -- and rename it to
better match other metadata-related tests.
(Note: the scope of function-local metadata changed drastically during
the metadata/value split, but I didn't properly clean up this testcase.
Most of the IR in this file, while invalid for debug info intrinsics,
used to provide coverage for various (now illegal) forms of
function-local metadata.)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232290 91177308-0d34-0410-b5e6-96231b3b80d8
Summary: This is a first step toward getting proper support for aggregate loads and stores.
Test Plan: Added unittests
Reviewers: reames, chandlerc
Reviewed By: chandlerc
Subscribers: majnemer, joker.eph, chandlerc, llvm-commits
Differential Revision: http://reviews.llvm.org/D7780
Patch by Amaury Sechet
From: Mehdi Amini <mehdi.amini@apple.com>
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232284 91177308-0d34-0410-b5e6-96231b3b80d8
