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
