Summary:
When simplifying unconditional branches from empty blocks, we pre-test if the
BB belongs to a set of loop headers and keep the block to prevent passes from
destroying canonical loop structure. However, the current algorithm fails if
the destination of the branch is a loop header. Especially when such a loop's
latch block is folded into loop header it results in additional backedges and
LoopSimplify turns it into a nested loop which prevent later optimizations
from being applied (e.g., loop unrolling and loop interleaving).
This patch augments the existing algorithm by further checking if the
destination of the branch belongs to a set of loop headers and defer
eliminating it if yes to LateSimplifyCFG.
Fixes PR33605: https://bugs.llvm.org/show_bug.cgi?id=33605
Reviewers: efriedma, mcrosier, pacxx, hsung, davidxl
Reviewed By: efriedma
Subscribers: ashutosh.nema, gberry, javed.absar, llvm-commits
Differential Revision: https://reviews.llvm.org/D35411
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@308422 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
When we runtime unroll with multiple exit blocks, we also need to update the
immediate dominators of the immediate successors of the exit blocks.
Reviewers: reames, mkuper, mzolotukhin, apilipenko
Reviewed by: mzolotukhin
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D35304
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307909 91177308-0d34-0410-b5e6-96231b3b80d8
Refactored the code and separated out a function
`canSafelyUnrollMultiExitLoop` to reduce redundant checks and make it
easier to add profitability heuristics later.
Added tests to runtime unrolling to make sure that unrolling for
multi-exit loops is not done unless the option
-unroll-runtime-multi-exit is true.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307843 91177308-0d34-0410-b5e6-96231b3b80d8
The loop structure for the outer loop does not contain the epilog
preheader when we try to unroll inner loop with multiple exits and
epilog code is generated. For now, we just bail out in such cases.
Added a test case that shows the problem. Without this bailout, we would
trip on assert saying LCSSA form is incorrect for outer loop.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307676 91177308-0d34-0410-b5e6-96231b3b80d8
When unrolling under multiple exits which is under off-by-default option,
the assert that checks for VMap entry in loop exit values is too strong.
(assert if VMap entry did not exist, the value should be a
constant). However, values derived from
constants or from values outside loop, does not have a VMap entry too.
Removed the assert and added a testcase showcasing the property for
non-constant values.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307542 91177308-0d34-0410-b5e6-96231b3b80d8
With the NFC refactoring in rL307417 (git SHA 987dd01), all the logic
is in place to support multiple exit/exiting blocks when prolog
remainder is generated.
This patch removed the assert that multiple exit blocks unrolling is only
supported when epilog remainder is generated.
Also, added test runs and checks with PROLOG prefix in
runtime-loop-multiple-exits.ll test cases.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307435 91177308-0d34-0410-b5e6-96231b3b80d8
Currently, we do not support multiple exiting blocks to the
latch exit block. However, this bailout wasn't triggered when we had a
unique exit block (which is the latch exit), with multiple exiting
blocks to that unique exit.
Moved the bailout so that it's triggered in both cases and added
testcase.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307291 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
Runtime unrolling is done for loops with a single exit block and a
single exiting block (and this exiting block should be the latch block).
This patch adds logic to support unrolling in the presence of multiple exit
blocks (which also means multiple exiting blocks).
Currently this is under an off-by-default option and is supported when
epilog code is generated. Support in presence of prolog code will be in
a future patch (we just need to add more tests, and update comments).
This patch is essentially an implementation patch. I have not added any
heuristic (in terms of branches added or code size) to decide when
this should be enabled.
Reviewers: mkuper, sanjoy, reames, evstupac
Reviewed by: reames
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D33001
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306846 91177308-0d34-0410-b5e6-96231b3b80d8
The current Loop Unroll implementation works with loops having a
single latch that contains a conditional branch to a block outside
the loop (the other successor is, by defition of latch, the header).
If this precondition doesn't hold, avoid unrolling the loop as
the code is not ready to handle such circumstances.
Differential Revision: https://reviews.llvm.org/D32261
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301239 91177308-0d34-0410-b5e6-96231b3b80d8
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
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300446 91177308-0d34-0410-b5e6-96231b3b80d8
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
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300441 91177308-0d34-0410-b5e6-96231b3b80d8
Currently the default C calling convention functions are treated
the same as compute kernels. Make this explicit so the default
calling convention can be changed to a non-kernel.
Converted with perl -pi -e 's/define void/define amdgpu_kernel void/'
on the relevant test directories (and undoing in one place that actually
wanted a non-kernel).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298444 91177308-0d34-0410-b5e6-96231b3b80d8
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
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297122 91177308-0d34-0410-b5e6-96231b3b80d8
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
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296898 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
Extend -unroll-partial-threshold to 200 for runtime-loop3.ll test
as epilogue unroll initially add 1 more IV to the loop.
From: Evgeny Stupachenko <evstupac@gmail.com>
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296803 91177308-0d34-0410-b5e6-96231b3b80d8
Exit loop analysis early if suitable private access found.
Do not account for GEPs which are invariant to loop induction variable.
Do not account for Allocas which are too big to fit into register file anyway.
Add option for tuning: -amdgpu-unroll-threshold-private.
Differential Revision: https://reviews.llvm.org/D29473
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293991 91177308-0d34-0410-b5e6-96231b3b80d8
factory functions for the two modes the loop unroller is actually used
in in-tree: simplified full-unrolling and the entire thing including
partial unrolling.
I've also wired these up to nice names so you can express both of these
being in a pipeline easily. This is a precursor to actually enabling
these parts of the O2 pipeline.
Differential Revision: https://reviews.llvm.org/D28897
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293136 91177308-0d34-0410-b5e6-96231b3b80d8
Even when we don't create a remainder loop (that is, when we unroll by 2), we
may duplicate nested loops into the remainder. This is complicated by the fact
the remainder may itself be either inserted into an outer loop, or at the top
level. In the latter case, we may need to create new top-level loops.
Differential Revision: https://reviews.llvm.org/D29156
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loops.
We do this by reconstructing the newly added loops after the unroll
completes to avoid threading pass manager details through all the mess
of the unrolling infrastructure.
I've enabled some extra assertions in the LPM to try and catch issues
here and enabled a bunch of unroller tests to try and make sure this is
sane.
Currently, I'm manually running loop-simplify when needed. That should
go away once it is folded into the LPM infrastructure.
Differential Revision: https://reviews.llvm.org/D28848
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293011 91177308-0d34-0410-b5e6-96231b3b80d8
Running non-LCSSA-preserving LoopSimplify followed by LCSSA on (roughly) the
same loop is incorrect, since LoopSimplify may break LCSSA arbitrarily higher
in the loop nest. Instead, run LCSSA first, and then run LCSSA-preserving
LoopSimplify on the result.
This fixes PR31718.
Differential Revision: https://reviews.llvm.org/D29055
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292854 91177308-0d34-0410-b5e6-96231b3b80d8
Summary: Partial unrolling should have separate threshold with full unrolling.
Reviewers: efriedma, mzolotukhin
Reviewed By: efriedma, mzolotukhin
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D28831
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292293 91177308-0d34-0410-b5e6-96231b3b80d8
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
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290833 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
The current loop complete unroll algorithm checks if unrolling complete will reduce the runtime by a certain percentage. If yes, it will apply a fixed boosting factor to the threshold (by discounting cost). The problem for this approach is that the threshold abruptly. This patch makes the boosting factor a function of runtime reduction percentage, capped by a fixed threshold. In this way, the threshold changes continuously.
The patch also simplified the code by reducing one parameter in UP.
The patch only affects code-gen of two speccpu2006 benchmark:
445.gobmk binary size decreases 0.08%, no performance change.
464.h264ref binary size increases 0.24%, no performance change.
Reviewers: mzolotukhin, chandlerc
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D26989
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290737 91177308-0d34-0410-b5e6-96231b3b80d8
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
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@288274 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
For flat loop, even if it is hot, it is not a good idea to unroll in runtime, thus we set a lower partial unroll threshold.
For hot loop, we set a higher unroll threshold and allows expensive tripcount computation to allow more aggressive unrolling.
Reviewers: davidxl, mzolotukhin
Subscribers: sanjoy, mehdi_amini, llvm-commits
Differential Revision: https://reviews.llvm.org/D26527
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@287186 91177308-0d34-0410-b5e6-96231b3b80d8
When we have a loop with a known upper bound on the number of iterations, and
furthermore know that either the number of iterations will be either exactly
that upper bound or zero, then we can fully unroll up to that upper bound
keeping only the first loop test to check for the zero iteration case.
Most of the work here is in plumbing this 'max-or-zero' information from the
part of scalar evolution where it's detected through to loop unrolling. I've
also gone for the safe default of 'false' everywhere but howManyLessThans which
could probably be improved.
Differential Revision: https://reviews.llvm.org/D25682
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284818 91177308-0d34-0410-b5e6-96231b3b80d8
Reappy r284044 after revert in r284051. Krzysztof fixed the error in r284049.
The original summary:
This patch tries to fully unroll loops having break statement like this
for (int i = 0; i < 8; i++) {
if (a[i] == value) {
found = true;
break;
}
}
GCC can fully unroll such loops, but currently LLVM cannot because LLVM only
supports loops having exact constant trip counts.
The upper bound of the trip count can be obtained from calling
ScalarEvolution::getMaxBackedgeTakenCount(). Part of the patch is the
refactoring work in SCEV to prevent duplicating code.
The feature of using the upper bound is enabled under the same circumstance
when runtime unrolling is enabled since both are used to unroll loops without
knowing the exact constant trip count.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284053 91177308-0d34-0410-b5e6-96231b3b80d8
This patch tries to fully unroll loops having break statement like this
for (int i = 0; i < 8; i++) {
if (a[i] == value) {
found = true;
break;
}
}
GCC can fully unroll such loops, but currently LLVM cannot because LLVM only
supports loops having exact constant trip counts.
The upper bound of the trip count can be obtained from calling
ScalarEvolution::getMaxBackedgeTakenCount(). Part of the patch is the
refactoring work in SCEV to prevent duplicating code.
The feature of using the upper bound is enabled under the same circumstance
when runtime unrolling is enabled since both are used to unroll loops without
knowing the exact constant trip count.
Differential Revision: https://reviews.llvm.org/D24790
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284044 91177308-0d34-0410-b5e6-96231b3b80d8
Summary: Debug info should *not* affect optimization decisions. This patch updates loop unroller cost model to make it not affected by debug info.
Reviewers: davidxl, mzolotukhin
Subscribers: haicheng, llvm-commits, mzolotukhin
Differential Revision: https://reviews.llvm.org/D25098
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@282894 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
When cloning blocks for prologue/epilogue we need to replicate the loop
structure from the original loop. It wasn't a problem for the innermost
loops, but it led to an incorrect loop info when we unrolled a loop with
a child loop - in this case created prologue-loop had a child loop, but
loop info didn't reflect that.
This fixes PR28888.
Reviewers: chandlerc, sanjoy, hfinkel
Subscribers: llvm-commits, silvas
Differential Revision: https://reviews.llvm.org/D24203
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280901 91177308-0d34-0410-b5e6-96231b3b80d8
As agreed in post-commit review of r265388, I'm switching the flag to
its original value until the 90% runtime performance regression on
SingleSource/Benchmarks/Stanford/Bubblesort is addressed.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@277524 91177308-0d34-0410-b5e6-96231b3b80d8
LoopUnroll is a loop pass, so the analysis of OptimizationRemarkEmitter
is added to the common function analysis passes that loop passes
depend on.
The BFI and indirectly BPI used in this pass is computed lazily so no
overhead should be observed unless -pass-remarks-with-hotness is used.
This is how the patch affects the O3 pipeline:
Dominator Tree Construction
Natural Loop Information
Canonicalize natural loops
Loop-Closed SSA Form Pass
Basic Alias Analysis (stateless AA impl)
Function Alias Analysis Results
Scalar Evolution Analysis
+ Lazy Branch Probability Analysis
+ Lazy Block Frequency Analysis
+ Optimization Remark Emitter
Loop Pass Manager
Rotate Loops
Loop Invariant Code Motion
Unswitch loops
Simplify the CFG
Dominator Tree Construction
Basic Alias Analysis (stateless AA impl)
Function Alias Analysis Results
Combine redundant instructions
Natural Loop Information
Canonicalize natural loops
Loop-Closed SSA Form Pass
Scalar Evolution Analysis
+ Lazy Branch Probability Analysis
+ Lazy Block Frequency Analysis
+ Optimization Remark Emitter
Loop Pass Manager
Induction Variable Simplification
Recognize loop idioms
Delete dead loops
Unroll loops
...
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@277203 91177308-0d34-0410-b5e6-96231b3b80d8
We just set PreserveLCSSA to always true since we don't have an
analogous method `mustPreserveAnalysisID(LCSSA)`.
Also port LoopInfo verifier pass to test LoopUnrollPass.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@276063 91177308-0d34-0410-b5e6-96231b3b80d8
Balaram Makam