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
If a lifetime.end marker occurs along one path through the extraction
region, but not another, then it's still incorrect to lift the marker,
because there is some path through the extracted function which would
ordinarily not reach the marker. If the call to the extracted function
is in a loop, unrolling can cause inputs to the function to become
optimized out as undef after the first iteration.
To prevent incorrect stack slot merging in the calling function, it
should be sufficient to lift lifetime.start markers for region inputs.
I've tested this theory out by doing a stage2 check-all with randomized
splitting enabled.
This is a follow-up to r353973, and there's additional context for this
change in https://reviews.llvm.org/D57834.
rdar://47896986
Differential Revision: https://reviews.llvm.org/D58253
llvm-svn: 354159
When CodeExtractor finds liftime markers referencing inputs to the
extraction region, it lifts these markers out of the region and inserts
them around the call to the extracted function (see r350420, PR39671).
However, it should *only* lift lifetime markers that are actually
present in the extraction region. I.e., if a start marker is present in
the extraction region but a corresponding end marker isn't (or vice
versa), only the start marker (or end marker, resp.) should be lifted.
Differential Revision: https://reviews.llvm.org/D57834
llvm-svn: 353973
Summary:
When compiling with profile data, ensure the split cold function gets
cold function_entry_count metadata (just use 0 since it should be cold).
Otherwise with function sections it will not be placed in the unlikely
text section with other cold code.
Reviewers: vsk
Subscribers: sebpop, hiraditya, davidxl, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D57900
llvm-svn: 353434
Resumes that are not reachable from a cleanup landing pad are considered
to be unreachable. It’s not safe to split them out.
rdar://47808235
llvm-svn: 353242
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
While a cold invoke itself and its unwind destination can't be
extracted, code which unconditionally executes before/after the invoke
may still be profitable to extract.
With cost model changes from D57125 applied, this gives a 3.5% increase
in split text across LNT+externals on arm64 at -Os.
llvm-svn: 352160
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
CodeExtractor permits extracting a region of blocks from a function even
when values defined within the region are used outside of it.
This is typically done by creating an alloca in the original function
and reloading the alloca after a call to the extracted function.
Wrap the reload in lifetime start/end markers to promote stack coloring.
Suggested by Sergei Kachkov!
Differential Revision: https://reviews.llvm.org/D56045
llvm-svn: 351621
Prior to r348205, extracting code regions with live output values was
disabled because of a miscompilation (PR39433). Lift the restriction as
PR39433 has been addressed.
Tested on LNT+externals, on a run of check-llvm in a stage2 build, and
with a full build of iOS (with hot/cold splitting enabled).
As a drive-by, remove an errant TODO.
llvm-svn: 351492
Resuming exception unwinding is roughly as unlikely as throwing an
exception.
Tested on LNT+externals (in particular, the C++ EH regression tests
provide end-to-end test coverage), as well as with a full build of iOS.
llvm-svn: 351491
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
Lifetime markers which reference inputs to the extraction region are not
safe to extract. Example ('rhs' will be extracted):
```
entry:
+------------+
| x = alloca |
| y = alloca |
+------------+
/ \
lhs: rhs:
+-------------------+ +-------------------+
| lifetime_start(x) | | lifetime_start(x) |
| use(x) | | lifetime_start(y) |
| lifetime_end(x) | | use(x, y) |
| lifetime_start(y) | | lifetime_end(y) |
| use(y) | | lifetime_end(x) |
| lifetime_end(y) | +-------------------+
+-------------------+
```
Prior to extraction, the stack coloring pass sees that the slots for 'x'
and 'y' are in-use at the same time. After extraction, the coloring pass
infers that 'x' and 'y' are *not* in-use concurrently, because markers
from 'rhs' are no longer available to help decide otherwise.
This leads to a miscompile, because the stack slots actually are in-use
concurrently in the extracted function.
Fix this by moving lifetime start/end markers for memory regions defined
in the calling function around the call to the extracted function.
Fixes llvm.org/PR39671 (rdar://45939472).
Differential Revision: https://reviews.llvm.org/D55967
llvm-svn: 350420
It's currently not safe to outline landingpad instructions (see
llvm.org/PR39917). Like @llvm.eh.typeid.for, the order and content of
previous landingpad instructions in a function alters the lowering of
subsequent landingpads by renumbering type info ID's. Outlining a
landingpad therefore breaks exception handling & unwinding.
llvm-svn: 348870
The splitting pass uses its 'unlikelyExecuted' predicate to statically
decide which blocks are cold.
- Do not treat noreturn calls as if they are cold unless they are actually
marked cold. This is motivated by functions like exit() and longjmp(), which
are not beneficial to outline.
- Do not treat inline asm as an outlining barrier. In practice asm("") is
frequently used to inhibit basic block merging; enabling outlining in this case
results in substantial memory savings.
- Treat invokes of cold functions as cold.
As a drive-by, remove the 'exceptionHandlingFunctions' predicate, because it's
no longer needed. The pass can identify & outline blocks dominated by EH pads,
so there's no need to special-case __cxa_begin_catch etc.
Differential Revision: https://reviews.llvm.org/D54244
llvm-svn: 348640
Algorithm: Identify maximal cold regions and put them in a worklist. If
a candidate region overlaps with another, discard it. While the worklist
is full, remove a single-entry sub-region from the worklist and attempt
to outline it. By the non-overlap property, this should not invalidate
parts of the domtree pertaining to other outlining regions.
Testing: LNT results on X86 are clean. With test-suite + externals, llvm
outlines 134KB pre-patch, and 352KB post-patch (+ ~2.6x). The file
483.xalancbmk/src/Constants.cpp stands out as an extreme case where llvm
outlines over 100 times in some functions (mostly EH paths). There was
not a significant performance impact pre vs. post-patch.
Differential Revision: https://reviews.llvm.org/D53887
llvm-svn: 348639
Treat terminators which resume exception propagation as returning instructions
(at least, for the purposes of marking outlined functions `noreturn`). This is
to avoid inserting traps after calls to outlined functions which unwind.
rdar://46129950
llvm-svn: 348404
If a PHI node out of extracted region has multiple incoming values from it,
split this PHI on two parts. First PHI has incomings only from region and
extracts with it (they are placed to the separate basic block that added to the
list of outlined), and incoming values in original PHI are replaced by first
PHI. Similar solution is already used in CodeExtractor for PHIs in entry block
(severSplitPHINodes method). It covers PR39433 bug.
Patch by Sergei Kachkov!
Differential Revision: https://reviews.llvm.org/D55018
llvm-svn: 348205
This eliminates the outlining penalty for llvm.trap/unreachable, because
callers no longer have to emit cleanup/ret instructions after calling an
outlined `noreturn` function.
rdar://45523626
llvm-svn: 346421
The lowering for a call to eh_typeid_for changes when it's moved from
one function to another.
There are several proposals for fixing this issue in llvm.org/PR39545.
Until some solution is in place, do not allow CodeExtractor to extract
calls to eh_typeid_for, as that results in serious miscompilations.
llvm-svn: 346256
When CodeExtractor moves instructions to a new function, debug
intrinsics referring to those instructions within the parent function
become invalid.
This results in the same verifier failure which motivated r344545, about
function-local metadata being used in the wrong function.
llvm-svn: 346255
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
It can be profitable to outline single-block cold regions because they
may be large.
Allow outlining single-block regions if they have over some threshold of
non-debug, non-terminator instructions. I chose 3 as the threshold after
experimenting with several internal frameworks.
In practice, reducing the threshold further did not give much
improvement, whereas increasing it resulted in substantial regressions.
Differential Revision: https://reviews.llvm.org/D53824
llvm-svn: 345524
The current splitting algorithm works in three stages:
1) Identify cold blocks, then
2) Use forward/backward propagation to mark hot blocks, then
3) Grow a SESE region of blocks *outside* of the set of hot blocks and
start outlining.
While testing this pass on Apple internal frameworks I noticed that some
kinds of control flow (e.g. loops) are never outlined, even though they
unconditionally lead to / follow cold blocks. I noticed two other issues
related to how cold regions are identified:
- An inconsistency can arise in the internal state of the hotness
propagation stage, as a block may end up in both the ColdBlocks set
and the HotBlocks set. Further inconsistencies can arise as these sets
do not match what's in ProfileSummaryInfo.
- It isn't necessary to limit outlining to single-exit regions.
This patch teaches the splitting algorithm to identify maximal cold
regions and outline them. A maximal cold region is defined as the set of
blocks post-dominated by a cold sink block, or dominated by that sink
block. This approach can successfully outline loops in the cold path. As
a side benefit, it maintains less internal state than the current
approach.
Due to a limitation in CodeExtractor, blocks within the maximal cold
region which aren't dominated by a single entry point (a so-called "max
ancestor") are filtered out.
Results:
- X86 (LNT + -Os + externals): 134KB of TEXT were outlined compared to
47KB pre-patch, or a ~3x improvement. Did not see a performance impact
across two runs.
- AArch64 (LNT + -Os + externals + Apple-internal benchmarks): 149KB
of TEXT were outlined. Ditto re: performance impact.
- Outlining results improve marginally in the internal frameworks I
tested.
Follow-ups:
- Outline more than once per function, outline large single basic
blocks, & try to remove unconditional branches in outlined functions.
Differential Revision: https://reviews.llvm.org/D53627
llvm-svn: 345209
Summary:
The current default of appending "_"+entry block label to the new
extracted cold function breaks demangling. Change the deliminator from
"_" to "." to enable demangling. Because the header block label will
be empty for release compile code, use "extracted" after the "." when
the label is empty.
Additionally, add a mechanism for the client to pass in an alternate
suffix applied after the ".", and have the hot cold split pass use
"cold."+Count, where the Count is currently 1 but can be used to
uniquely number multiple cold functions split out from the same function
with D53588.
Reviewers: sebpop, hiraditya
Subscribers: llvm-commits, erik.pilkington
Differential Revision: https://reviews.llvm.org/D53534
llvm-svn: 345178
Outlined code is cold by assumption, so it makes sense to optimize it
for minimal code size rather than performance.
After r344869 moved the splitting pass to the end of the IR pipeline,
this does not result in much of a code size reduction. This is probably
because a comparatively small number backend transforms make use of the
MinSize hint.
Running LNT on x86_64, I see that 33/1020 binaries shrink for a total of
919 bytes of TEXT reduction. I didn't measure a significant performance
impact.
Differential Revision: https://reviews.llvm.org/D53518
llvm-svn: 345072
Summary:
r344558 added some CHECK statements to split-cold-2.ll, but didn't add
any invocations of FileCheck. Add those here.
Reviewers: sebpop
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D53505
llvm-svn: 344928
Make the code of blockEndsInUnreachable to match the function
blockEndsInUnreachable in CodeGen/BranchFolding.cpp. I also have
added a note to make sure the code of this function will not be
modified unless the back-end version is also modified.
An early return before outlining has been added to avoid
outlining the full function body when the first block in the
function is marked cold.
The static analysis of cold code has been amended to avoid
marking the whole function as cold by back-propagation
because the back-propagation would mark blocks with return
statements as cold.
The patch adds debug statements to help discover these problems.
Differential Revision: https://reviews.llvm.org/D52904
llvm-svn: 344558
Variable updates within the outlined function are invisible to
debuggers. This could be improved by defining a DISubprogram for the
new function. For the moment, simply erase the debug intrinsics instead.
This fixes verifier failures about function-local metadata being used in
the wrong function, seen while testing the hot/cold splitting pass.
rdar://45142482
Differential Revision: https://reviews.llvm.org/D53267
llvm-svn: 344545
Modified the testcases to use both pass managers
Use single commandline flag for both pass managers.
Differential Revision: https://reviews.llvm.org/D52708
Reviewers: sebpop, tejohnson, brzycki, SirishP
Reviewed By: tejohnson, brzycki
llvm-svn: 343662
The test used to fail with an invalid phi node: the two predecessors were outlined
and the SSA representation was left invalid. The patch adds the exit block to the
cold region.
llvm-svn: 342277
Find cold blocks based on profile information (or optionally with static analysis).
Forward propagate profile information to all cold-blocks.
Outline a cold region.
Set calling conv and prof hint for the callsite of the outlined function.
Worked in collaboration with: Sebastian Pop <s.pop@samsung.com>
Differential Revision: https://reviews.llvm.org/D50658
llvm-svn: 341669
Eric Christopher