This is a follow-up to b71edfaa4ec3c998aadb35255ce2f60bba2940b0
since I forgot the lit.local.cfg files in that one.
Reformatting is done with `black`.
If you end up having problems merging this commit because you
have made changes to a python file, the best way to handle that
is to run git checkout --ours <yourfile> and then reformat it
with black.
If you run into any problems, post to discourse about it and
we will try to help.
RFC Thread below:
https://discourse.llvm.org/t/rfc-document-and-standardize-python-code-style
Reviewed By: barannikov88, kwk
Differential Revision: https://reviews.llvm.org/D150762
This broke Chromium's PGO build, it seems because hot-cold-splitting got turned
on unintentionally. See comment on the code review for repro etc.
> This patch adds -f[no-]split-cold-code CC1 options to clang. This allows
> the splitting pass to be toggled on/off. The current method of passing
> `-mllvm -hot-cold-split=true` to clang isn't ideal as it may not compose
> correctly (say, with `-O0` or `-Oz`).
>
> To implement the -fsplit-cold-code option, an attribute is applied to
> functions to indicate that they may be considered for splitting. This
> removes some complexity from the old/new PM pipeline builders, and
> behaves as expected when LTO is enabled.
>
> Co-authored by: Saleem Abdulrasool <compnerd@compnerd.org>
> Differential Revision: https://reviews.llvm.org/D57265
> Reviewed By: Aditya Kumar, Vedant Kumar
> Reviewers: Teresa Johnson, Aditya Kumar, Fedor Sergeev, Philip Pfaffe, Vedant Kumar
This reverts commit 273c299d5d649a0222fbde03c9a41e41913751b4.
This patch adds -f[no-]split-cold-code CC1 options to clang. This allows
the splitting pass to be toggled on/off. The current method of passing
`-mllvm -hot-cold-split=true` to clang isn't ideal as it may not compose
correctly (say, with `-O0` or `-Oz`).
To implement the -fsplit-cold-code option, an attribute is applied to
functions to indicate that they may be considered for splitting. This
removes some complexity from the old/new PM pipeline builders, and
behaves as expected when LTO is enabled.
Co-authored by: Saleem Abdulrasool <compnerd@compnerd.org>
Differential Revision: https://reviews.llvm.org/D57265
Reviewed By: Aditya Kumar, Vedant Kumar
Reviewers: Teresa Johnson, Aditya Kumar, Fedor Sergeev, Philip Pfaffe, Vedant Kumar
As it's causing some bot failures (and per request from kbarton).
This reverts commit r358543/ab70da07286e618016e78247e4a24fcb84077fda.
llvm-svn: 358546
Splitting can make sanitizer errors harder to understand, as the
trapping instruction may not be in the function where the bug was
detected.
rdar://48142697
llvm-svn: 354931
The main goal of the model is to avoid *increasing* function size, as
that would eradicate any memory locality benefits from splitting. This
happens when:
- There are too many inputs or outputs to the cold region. Argument
materialization and reloads of outputs have a cost.
- The cold region has too many distinct exit blocks, causing a large
switch to be formed in the caller.
- The code size cost of the split code is less than the cost of a
set-up call.
A secondary goal is to prevent excessive overall binary size growth.
With the cost model in place, I experimented to find a splitting
threshold that works well in practice. To make warm & cold code easily
separable for analysis purposes, I moved split functions to a "cold"
section. I experimented with thresholds between [0, 4] and set the
default to the threshold which minimized geomean __text size.
Experiment data from building LNT+externals for X86 (N = 639 programs,
all sizes in bytes):
| Configuration | __text geom size | __cold geom size | TEXT geom size |
| **-Os** | 1736.3 | 0, n=0 | 10961.6 |
| -Os, thresh=0 | 1740.53 | 124.482, n=134 | 11014 |
| -Os, thresh=1 | 1734.79 | 57.8781, n=90 | 10978.6 |
| -Os, thresh=2 | ** 1733.85 ** | 65.6604, n=61 | 10977.6 |
| -Os, thresh=3 | 1733.85 | 65.3071, n=61 | 10977.6 |
| -Os, thresh=4 | 1735.08 | 67.5156, n=54 | 10965.7 |
| **-Oz** | 1554.4 | 0, n=0 | 10153 |
| -Oz, thresh=2 | ** 1552.2 ** | 65.633, n=61 | 10176 |
| **-O3** | 2563.37 | 0, n=0 | 13105.4 |
| -O3, thresh=2 | ** 2559.49 ** | 71.1072, n=61 | 13162.4 |
Picking thresh=2 reduces the geomean __text section size by 0.14% at
-Os, -Oz, and -O3 and causes ~0.2% growth in the TEXT segment. Note that
TEXT size is page-aligned, whereas section sizes are byte-aligned.
Experiment data from building LNT+externals for ARM64 (N = 558 programs,
all sizes in bytes):
| Configuration | __text geom size | __cold geom size | TEXT geom size |
| **-Os** | 1763.96 | 0, n=0 | 42934.9 |
| -Os, thresh=2 | ** 1760.9 ** | 76.6755, n=61 | 42934.9 |
Picking thresh=2 reduces the geomean __text section size by 0.17% at
-Os and causes no growth in the TEXT segment.
Measurements were done with D57082 (r352080) applied.
Differential Revision: https://reviews.llvm.org/D57125
llvm-svn: 352228
If an inherently cold function is found, mark it as cold. For now this
means applying the `cold` and `minsize` attributes.
As a drive-by, revisit and clean up the criteria for considering a
function for splitting. Add tests.
llvm-svn: 351623
This gets rid of the brittle/mysterious calls to @sink()/@sideeffect()
peppered throughout the test cases. They are no longer needed to force
splitting to occur.
llvm-svn: 351480
Using TargetTransformInfo allows the splitting pass to factor in the
code size cost of instructions as it decides whether or not outlining is
profitable.
This did not regress the overall amount of outlining seen on the handful
of internal frameworks I tested.
Thanks to Jun Bum Lim for suggesting this!
Differential Revision: https://reviews.llvm.org/D53835
llvm-svn: 346108
