This reverts commit 3f3017e because there's a failure on peel-loop-nests.ll
with LLVM_ENABLE_EXPENSIVE_CHECKS on.
Differential Revision: https://reviews.llvm.org/D70304
Summary:
Current peeling implementation bails out in case of loop nests.
The patch introduces a field in TargetTransformInfo structure that
certain targets can use to relax the constraints if it's
profitable (disabled by default).
Also additional option is added to enable peeling manually for
experimenting and testing purposes.
Reviewers: fhahn, lebedev.ri, xbolva00
Reviewed By: xbolva00
Subscribers: xbolva00, hiraditya, zzheng, llvm-commits
Differential Revision: https://reviews.llvm.org/D70304
Summary:
I believe this bisects to https://reviews.llvm.org/D44983
(`[LoopUnroll] Only peel if a predicate becomes known in the loop body.`)
While that revision did contain tests that showed arguably-subpar peeling
for [in]equality predicates that [not] happen in the middle of the loop,
it also disabled peeling for the *first* loop iteration,
because latch would be canonicalized to [in]equality comparison..
That was intentional as per https://reviews.llvm.org/D44983#1059583.
I'm not 100% sure that i'm using correct checks here,
but this fix appears to be going in the right direction..
Let me know if i'm missing some checks here..
Fixes [[ https://bugs.llvm.org/show_bug.cgi?id=43840 | PR43840 ]].
Reviewers: fhahn, mkazantsev, efriedma
Reviewed By: fhahn
Subscribers: xbolva00, hiraditya, zzheng, llvm-commits, fhahn
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D69617
Current peeling cost model can decide to peel off not all iterations
but only some of them to eliminate conditions on phi. At the same time
if any peeling happens the door for further unroll/peel optimizations on that
loop closes because the part of the code thinks that if peeling happened
it is profile based peeling and all iterations are peeled off.
To resolve this inconsistency the patch provides the flag which states whether
the full peeling basing on profile is enabled or not and peeling cost model
is able to modify this field like it does not PeelCount.
In a separate patch I will introduce an option to allow/disallow peeling basing
on profile.
To avoid infinite loop peeling the patch tracks the total number of peeled iteration
through llvm.loop.peeled.count loop metadata.
Reviewers: reames, fhahn
Reviewed By: reames
Subscribers: hiraditya, zzheng, dmgreen, llvm-commits
Differential Revision: https://reviews.llvm.org/D64972
llvm-svn: 367647
We'd like to determine the idom of exit block after peeling one iteration.
Let Exit is exit block.
Let ExitingSet - is a set of predecessors of Exit block. They are exiting blocks.
Let Latch' and ExitingSet' are copies after a peeling.
We'd like to find an idom'(Exit) - idom of Exit after peeling.
It is an evident that idom'(Exit) will be the nearest common dominator of ExitingSet and ExitingSet'.
idom(Exit) is a nearest common dominator of ExitingSet.
idom(Exit)' is a nearest common dominator of ExitingSet'.
Taking into account that we have a single Latch, Latch' will dominate Header and idom(Exit).
So the idom'(Exit) is nearest common dominator of idom(Exit)' and Latch'.
All these basic blocks are in the same loop, so what we find is
(nearest common dominator of idom(Exit) and Latch)'.
Reviewers: reames, fhahn
Reviewed By: reames
Subscribers: hiraditya, zzheng, llvm-commits
Differential Revision: https://reviews.llvm.org/D65292
llvm-svn: 367044
Current algorithm to update branch weights of latch block and its copies is
based on the assumption that number of peeling iterations is approximately equal
to trip count.
However it is not correct. According to profitability check in one case we can decide to peel
in case it helps to reduce the number of phi nodes. In this case the number of peeled iteration
can be less then estimated trip count.
This patch introduces another way to set the branch weights to peeled of branches.
Let F is a weight of the edge from latch to header.
Let E is a weight of the edge from latch to exit.
F/(F+E) is a probability to go to loop and E/(F+E) is a probability to go to exit.
Then, Estimated TripCount = F / E.
For I-th (counting from 0) peeled off iteration we set the the weights for
the peeled latch as (TC - I, 1). It gives us reasonable distribution,
The probability to go to exit 1/(TC-I) increases. At the same time
the estimated trip count of remaining loop reduces by I.
As a result after peeling off N iteration the weights will be
(F - N * E, E) and trip count of loop becomes
F / E - N or TC - N.
The idea is taken from the review of the patch D63918 proposed by Philip.
Reviewers: reames, mkuper, iajbar, fhahn
Reviewed By: reames
Subscribers: hiraditya, zzheng, llvm-commits
Differential Revision: https://reviews.llvm.org/D64235
llvm-svn: 366665
It is possible that loop exit has two predecessors in a loop body.
In this case after the peeling the iDom of the exit should be a clone of
iDom of original exit but no a clone of a block coming to this exit.
Reviewers: reames, fhahn
Reviewed By: reames
Subscribers: hiraditya, zzheng, llvm-commits
Differential Revision: https://reviews.llvm.org/D64618
llvm-svn: 366050
This CL enables peeling of the loop with multiple exits where
one exit should be from latch and others are basic blocks with
call to deopt.
The peeling is enabled under the flag which is false by default.
Reviewers: reames, mkuper, iajbar, fhahn
Reviewed By: reames
Subscribers: xbolva00, hiraditya, zzheng, llvm-commits
Differential Revision: https://reviews.llvm.org/D63923
llvm-svn: 366048
This patch modifies the loop peeling transformation so that
it does not expect that there is only one loop exit from latch.
It modifies only transformation. Update of branch weights remains
only for exit from latch.
The motivation is that in follow-up patch I plan to enable loop peeling for
loops with multiple exits but only if other exits then from latch one goes to
block with call to deopt.
For now this patch is NFC.
Reviewers: reames, mkuper, iajbar, fhahn
Reviewed By: reames, fhahn
Subscribers: zzheng, llvm-commits
Differential Revision: https://reviews.llvm.org/D63921
llvm-svn: 365441
Summary:
There is PHINode::getBasicBlockIndex() and PHINode::setIncomingValue()
but no function to replace incoming value for a specified BasicBlock*
predecessor.
Clearly, there are a lot of places that could use that functionality.
Reviewer: craig.topper, lebedev.ri, Meinersbur, kbarton, fhahn
Reviewed By: Meinersbur, fhahn
Subscribers: fhahn, hiraditya, zzheng, jsji, llvm-commits
Tag: LLVM
Differential Revision: https://reviews.llvm.org/D63338
llvm-svn: 363566
Summary:
Preserve MemorySSA in LoopSimplify, in the old pass manager, if the analysis is available.
Do not preserve it in the new pass manager.
Update tests.
Subscribers: nemanjai, jlebar, javed.absar, Prazek, kbarton, zzheng, jsji, llvm-commits, george.burgess.iv, chandlerc
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D60833
llvm-svn: 360270
The test case requires the peeled loop to be forgotten after peeling,
even though it does not have a parent. When called via the unroller,
SE->forgetTopmostLoop is also called, so the test case would also pass
without any SCEV invalidation, but peelLoop is exposed as utility
function. Also, in the test case, simplifyLoop will make changes,
removing the loop from SCEV, but it is better to not rely on this
behavior.
Reviewers: sanjoy, mkazantsev
Reviewed By: mkazantsev
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D58192
llvm-svn: 354031
to reflect the new license.
We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.
Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.
llvm-svn: 351636
This verification is linear in the size of the function, so it can cause
a quadratic compile-time explosion in a function with many loops to
unroll.
Differential Revision: https://reviews.llvm.org/D54732
llvm-svn: 349871
The DEBUG() macro is very generic so it might clash with other projects.
The renaming was done as follows:
- git grep -l 'DEBUG' | xargs sed -i 's/\bDEBUG\s\?(/LLVM_DEBUG(/g'
- git diff -U0 master | ../clang/tools/clang-format/clang-format-diff.py -i -p1 -style LLVM
- Manual change to APInt
- Manually chage DOCS as regex doesn't match it.
In the transition period the DEBUG() macro is still present and aliased
to the LLVM_DEBUG() one.
Differential Revision: https://reviews.llvm.org/D43624
llvm-svn: 332240
We've been running doxygen with the autobrief option for a couple of
years now. This makes the \brief markers into our comments
redundant. Since they are a visual distraction and we don't want to
encourage more \brief markers in new code either, this patch removes
them all.
Patch produced by
for i in $(git grep -l '\\brief'); do perl -pi -e 's/\\brief //g' $i & done
Differential Revision: https://reviews.llvm.org/D46290
llvm-svn: 331272
If a predicate does not become known after peeling, peeling is unlikely
to be beneficial.
Reviewers: mcrosier, efriedma, mkazantsev, junbuml
Reviewed By: mkazantsev
Differential Revision: https://reviews.llvm.org/D44983
llvm-svn: 330250
For Hexagon, peeling loops with small runtime trip count is beneficial for our
benchmarks. We set PeelCount in HexagonTargetInfo.cpp and we use PeelCount set
by the target for computing the desired peel count.
Differential Revision: https://reviews.llvm.org/D44880
llvm-svn: 329042
For Hexagon, peeling loops with small runtime trip count is beneficial for our
benchmarks. We set PeelCount in HexagonTargetInfo.cpp and we use PeelCount set
by the target for computing the desired peel count.
Differential Revision: https://reviews.llvm.org/D44880
llvm-svn: 328854
We check `canPeel` twice: when evaluating the number of iterations to be peeled
and within the method `peelLoop` that performs peeling. This method is only
executed if the calculated peel count is positive. Thus, the check in `peelLoop` can
never fail. This patch replaces this check with an assert.
Differential Revision: https://reviews.llvm.org/D44919
Reviewed By: fhahn
llvm-svn: 328615
If the loop body contains conditions of the form IndVar < #constant, we
can remove the checks by peeling off #constant iterations.
This improves codegen for PR34364.
Reviewers: mkuper, mkazantsev, efriedma
Reviewed By: mkazantsev
Differential Revision: https://reviews.llvm.org/D43876
llvm-svn: 327671
Removes verifyDomTree, using assert(verify()) everywhere instead, and
changes verify a little to always run IsSameAsFreshTree first in order
to print good output when we find errors. Also adds verifyAnalysis for
PostDomTrees, which will allow checking of PostDomTrees it the same way
we check DomTrees and MachineDomTrees.
Differential Revision: https://reviews.llvm.org/D41298
llvm-svn: 326315
Summary:
This replaces calls to getEntryCount().hasValue() with hasProfileData
that does the same thing. This refactoring is useful to do before adding
synthetic function entry counts but also a useful cleanup IMO even
otherwise. I have used hasProfileData instead of hasRealProfileData as
David had earlier suggested since I think profile implies "real" and I
use the phrase "synthetic entry count" and not "synthetic profile count"
but I am fine calling it hasRealProfileData if you prefer.
Reviewers: davidxl, silvas
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D41461
llvm-svn: 321331
This patch is a generalization of the improvement introduced in rL296898.
Previously, we were able to peel one iteration of a loop to get rid of a Phi that becomes
an invariant on the 2nd iteration. In more general case, if a Phi becomes invariant after
N iterations, we can peel N times and turn it into invariant.
In order to do this, we for every Phi in loop's header we define the Invariant Depth value
which is calculated as follows:
Given %x = phi <Inputs from above the loop>, ..., [%y, %back.edge].
If %y is a loop invariant, then Depth(%x) = 1.
If %y is a Phi from the loop header, Depth(%x) = Depth(%y) + 1.
Otherwise, Depth(%x) is infinite.
Notice that if we peel a loop, all Phis with Depth = 1 become invariants,
and all other Phis with finite depth decrease the depth by 1.
Thus, peeling N first iterations allows us to turn all Phis with Depth <= N
into invariants.
Reviewers: reames, apilipenko, mkuper, skatkov, anna, sanjoy
Reviewed By: sanjoy
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D31613
llvm-svn: 300446
When peeling loops basing on phis becoming invariants, we make a wrong loop size check.
UP.Threshold should be compared against the total numbers of instructions after the transformation,
which is equal to 2 * LoopSize in case of peeling one iteration.
We should also check that the maximum allowed number of peeled iterations is not zero.
Reviewers: sanjoy, anna, reames, mkuper
Reviewed By: mkuper
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D31753
llvm-svn: 300441
Summary:
We should check if loop size allows us to peel at least one iteration
before we do so.
Patch by Max Kazantsev!
Reviewers: sanjoy, mkuper, efriedma
Reviewed By: mkuper
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D30632
llvm-svn: 297122
Summary:
If a loop contains a Phi node which has an invariant input from back
edge, it is profitable to peel such loops (rather than unroll them) to
use the advantage that this Phi is always invariant starting from 2nd
iteration. After the 1st iteration is peeled, other optimizations can
potentially simplify calculations with this invariant.
Patch by Max Kazantsev!
Reviewers: sanjoy, apilipenko, igor-laevsky, anna, mkuper, reames
Reviewed By: mkuper
Subscribers: mkuper, mzolotukhin, llvm-commits
Differential Revision: https://reviews.llvm.org/D30161
llvm-svn: 296898
Summary:
In current implementation the loop peeling happens after trip-count based partial unrolling and may
sometimes not happen at all due to it (for example, if trip count is known, but UP.Partial = false). This
is generally bad, the more than there are some situations where peeling is profitable even if the partial
unrolling is disabled.
This patch is a NFC which reorders peeling and partial unrolling application and prepares the code for
implementation of the said optimizations.
Patch by Max Kazantsev!
Reviewers: sanjoy, anna, reames, apilipenko, igor-laevsky, mkuper
Reviewed By: mkuper
Subscribers: mkuper, llvm-commits, mzolotukhin
Differential Revision: https://reviews.llvm.org/D30243
llvm-svn: 296897
With this change dominator tree remains in sync after each step of loop
peeling.
Differential Revision: https://reviews.llvm.org/D29029
llvm-svn: 292895
Mostly straightforward changes; we just didn't do the computation before.
One sort of interesting change in LoopUnroll.cpp: we weren't handling
dominance for children of the loop latch correctly, but
foldBlockIntoPredecessor hid the problem for complete unrolling.
Currently punting on loop peeling; made some minor changes to isolate
that problem to LoopUnrollPeel.cpp.
Adds a flag -unroll-verify-domtree; it verifies the domtree immediately
after we finish updating it. This is on by default for +Asserts builds.
Differential Revision: https://reviews.llvm.org/D28073
llvm-svn: 292447
Summary:
Regardless how the loop body weight is distributed, we should preserve
total loop body weight. i.e. we should have same weight reaching the body of the loop
or its duplicates in peeled and unpeeled case.
Reviewers: mkuper, davidxl, anemet
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D28179
llvm-svn: 290833
This implements PGO-driven loop peeling.
The basic idea is that when the average dynamic trip-count of a loop is known,
based on PGO, to be low, we can expect a performance win by peeling off the
first several iterations of that loop.
Unlike unrolling based on a known trip count, or a trip count multiple, this
doesn't save us the conditional check and branch on each iteration. However,
it does allow us to simplify the straight-line code we get (constant-folding,
etc.). This is important given that we know that we will usually only hit this
code, and not the actual loop.
This is currently disabled by default.
Differential Revision: https://reviews.llvm.org/D25963
llvm-svn: 288274
Arkady Shlykov