This is an alternative to the continous mode that was implemented in
D68351. This mode relies on padding and the ability to mmap a file over
the existing mapping which is generally only available on POSIX systems
and isn't suitable for other platforms.
This change instead introduces the ability to relocate counters at
runtime using a level of indirection. On every counter access, we add a
bias to the counter address. This bias is stored in a symbol that's
provided by the profile runtime and is initially set to zero, meaning no
relocation. The runtime can mmap the profile into memory at abitrary
location, and set bias to the offset between the original and the new
counter location, at which point every subsequent counter access will be
to the new location, which allows updating profile directly akin to the
continous mode.
The advantage of this implementation is that doesn't require any special
OS support. The disadvantage is the extra overhead due to additional
instructions required for each counter access (overhead both in terms of
binary size and performance) plus duplication of counters (i.e. one copy
in the binary itself and another copy that's mmapped).
Differential Revision: https://reviews.llvm.org/D69740
Emit a gap region beginning where the switch body begins. This sets line
execution counts in the areas between non-overlapping cases to 0.
This also removes some special handling of the first case in a switch:
these are now treated like any other case.
This does not resolve an outstanding issue with case statement regions
that do not end when a region is terminated. But it should address
llvm.org/PR44011.
Differential Revision: https://reviews.llvm.org/D70571
Make it possible to use online profile merging ("%m" mode) with
continuous sync ("%c" mode).
To implement this, the merged profile is locked in the runtime
initialization step and either a) filled out for the first time or b)
checked for compatibility. Then, the profile can simply be mmap()'d with
MAP_SHARED set. With the mmap() in place, counter updates from every
process which uses an image are mapped onto the same set of physical
pages assigned by the filesystem cache. After the mmap() is set up, the
profile is unlocked.
Differential Revision: https://reviews.llvm.org/D69586
Add support for continuously syncing profile counter updates to a file.
The motivation for this is that programs do not always exit cleanly. On
iOS, for example, programs are usually killed via a signal from the OS.
Running atexit() handlers after catching a signal is unreliable, so some
method for progressively writing out profile data is necessary.
The approach taken here is to mmap() the `__llvm_prf_cnts` section onto
a raw profile. To do this, the linker must page-align the counter and
data sections, and the runtime must ensure that counters are mapped to a
page-aligned offset within a raw profile.
Continuous mode is (for the moment) incompatible with the online merging
mode. This limitation is lifted in https://reviews.llvm.org/D69586.
Continuous mode is also (for the moment) incompatible with value
profiling, as I'm not sure whether there is interest in this and the
implementation may be tricky.
As I have not been able to test extensively on non-Darwin platforms,
only Darwin support is included for the moment. However, continuous mode
may "just work" without modification on Linux and some UNIX-likes. AIUI
the default value for the GNU linker's `--section-alignment` flag is set
to the page size on many systems. This appears to be true for LLD as
well, as its `no_nmagic` option is on by default. Continuous mode will
not "just work" on Fuchsia or Windows, as it's not possible to mmap() a
section on these platforms. There is a proposal to add a layer of
indirection to the profile instrumentation to support these platforms.
rdar://54210980
Differential Revision: https://reviews.llvm.org/D68351
Point out that --coverage and -ftest-coverage, which is what most people
are used to, do not enable clang's frontend based coverage pass.
Suggested by Benn Bolay!
llvm-svn: 294626
Flesh out the section on interpreting coverage reports, mention the
coverage export feature, and add notes on how to build llvm with
coverage turned on.
llvm-svn: 281988
A number of warnings still remain, but these were the last of the
"unlexable code"-related ones (AFAICT).
I changed a few examples in docs/UsersManual.rst to showcase
-Wextra-tokens because it's already documented (-Wmultichar isn't), and
the sphinx C lexer apparently can't handle char literals like 'ab'. It
seemed like a better overall approach than just marking the code blocks
as none or console.
llvm-svn: 273232
Mention that the code coverage tool becomes less precise whenever
unpredictable changes in control flow occur.
Thanks to Sean Silva for pointing this out!
llvm-svn: 271902
Nico Weber