Enabled loop interchange support for floating point reductions
if it is allowed to reorder floating point operations.
Previously when we encouter a floating point PHI node in the
outer loop exit block, we bailed out since we could not detect
floating point reductions in the early days. Now we remove this
limiation since we are able to detect floating point reductions.
Reviewed By: #loopoptwg, Meinersbur
Differential Revision: https://reviews.llvm.org/D117450
Currently loop interchange only supports loops with one inner loop
induction variable. This patch adds support for transformation with
more than one inner loop induction variables. The induction PHIs and
induction increment instructions are moved/duplicated properly to the
new outer header and the new outer latch, respectively.
Reviewed By: bmahjour
Differential Revision: https://reviews.llvm.org/D114917
This patch enables loop interchange with multiple outer loop
induction variables, and hence removes the limitation that only
a single outer loop induction variable is supported. In fact, it
turns out that the current pass already trivially supports multiple
outer indvars, which is the result of a previous patch
`https://reviews.llvm.org/D102743`. Therefore, this patch removed that
limitation and provides test cases for multiple outer indvars.
Reviewed By: bmahjour
Differential Revision: https://reviews.llvm.org/D114916
There was a limitation in legality that in the original inner loop latch,
no instruction was allowed between the induction variable increment
and the branch instruction. This is because we used to split the
inner latch at the induction variable increment instruction. Since
now we have split at the inner latch branch instruction and have
properly duplicated instructions over to the split block, we remove
this limitation.
Please refer to the test case updates to see how we now interchange
loops where instructions exist between the induction variable
increment and the branch instruction.
Reviewed By: bmahjour
Differential Revision: https://reviews.llvm.org/D115238
There was a limitation in legality that in the original inner loop latch,
no instruction was allowed between the induction variable increment
and the branch instruction. This is because we used to split the
inner latch at the induction variable increment instruction. Since
now we have split at the inner latch branch instruction and have
properly duplicated instructions over to the split block, we remove
this limitation.
Please refer to the test case updates to see how we now interchange
loops where instructions exist between the induction variable increment
and the branch instruction.
Reviewed By: bmahjour
Differential Revision: https://reviews.llvm.org/D115238
We already know that we need to check whether lcssa
phis are supported in inner loop exit block or in
outer loop exit block, and we have logic to check
them already. Presumably the inner loop latch does
not have lcssa phis and there is no code that deals
with lcssa phis in the inner loop latch. However,
that assumption is not true, when we have loops
with more than two-level nesting. This patch adds
checks for lcssa phis in the inner latch.
Reviewed By: Whitney
Differential Revision: https://reviews.llvm.org/D102300
This patch fixes pr43326 and pr48212.
Currently when we move reduction phis to the right place,
loop interchange assumes the first phi in loop headers is
an induction phi, skips the first phi and assumes the rest
of phis are candidate reduction phis to move. However, it
may not always be the case.
This patch loops over all phis in loop headers and considers
a phi node as a candidate reduction phi to move only when it
is indeed a reduction phi across outer and inner loop.
Reviewed By: Whitney
Differential Revision: https://reviews.llvm.org/D102743
This is a bugfix in the transformation phase.
If the original outer loop header branches to both the inner loop
(header) and the outer loop latch, and if there is an lcssa PHI
node outside the loop nest, then after interchange the new outer latch
will have an lcssa PHI node inserted which has two predecessors, i.e.,
the original outer header and the original outer latch. Currently
the transformation assumes it has only one predecessor (the original
outer latch) and crashes, since the inserted lcssa PHI node does
not take both predecessors as incoming BBs.
Reviewed By: Whitney
Differential Revision: https://reviews.llvm.org/D100792
This is a bug fix in legality check.
When we encounter triangular loops such as the following form:
for (int i = 0; i < m; i++)
for (int j = 0; j < i; j++), or
for (int i = 0; i < m; i++)
for (int j = 0; j*i < n; j++),
we should not perform interchange since the number of executions
of the loop body will be different before and after interchange,
resulting in incorrect results.
Reviewed By: bmahjour
Differential Revision: https://reviews.llvm.org/D101305
This is a bug fix in legality check.
When we encounter triangular loops such as the following form:
for (int i = 0; i < m; i++)
for (int j = 0; j < i; j++), or
for (int i = 0; i < m; i++)
for (int j = 0; j*i < n; j++),
we should not perform interchange since the number of executions of the loop body
will be different before and after interchange, resulting in incorrect results.
Reviewed By: bmahjour
Differential Revision: https://reviews.llvm.org/D101305
Patch by Artem Radzikhovskyy!
Allow delinearization of fixed sized arrays if we can prove that the GEP indices do not overflow the array dimensions. The checks applied are similar to the ones that are used for delinearization of parametric size arrays. Make sure that the GEP indices are non-negative and that they are smaller than the range of that dimension.
Changes Summary:
- Updated the LIT tests with more exact values, as we are able to delinearize and apply more exact tests
- profitability.ll - now able to delinearize in all cases, no need to use -da-disable-delinearization-checks flag and run the test twice
- loop-interchange-optimization-remarks.ll - in one of the cases we are able to delinearize without using -da-disable-delinearization-checks
- SimpleSIVNoValidityCheckFixedSize.ll - removed unnecessary "-da-disable-delinearization-checks" flag. Now can get the exact answer without it.
- SimpleSIVNoValidityCheckFixedSize.ll and PreliminaryNoValidityCheckFixedSize.ll - made negative tests more explicit, in order to demonstrate the need for "-da-disable-delinearization-checks" flag
Differential Revision: https://reviews.llvm.org/D101486
After loop interchange, the (old) outer loop header should not jump to
the `LoopExit`. Note that the old outer loop becomes the new inner loop
after interchange. If we branched to `LoopExit` then after interchange
we would jump directly from the (new) inner loop header to `LoopExit`
without executing the rest of outer loop.
This patch modifies adjustLoopBranches() such that the old outer
loop header (which becomes the new inner loop header) jumps to the
old inner loop latch which becomes the new outer loop latch after
interchange.
Reviewed By: bmahjour
Differential Revision: https://reviews.llvm.org/D98475
After loop interchange, the (old) outer loop header should not jump to
`LoopExit`. Note that the old outer loop becomes the new inner loop
after interchange. If we branched to `LoopExit` then after interchange
we would jump directly from the (new) inner loop header to `LoopExit`
without executing the rest of (new) outer loop.
This patch modifies adjustLoopBranches() such that the old outer
loop header (which becomes the new inner loop header) jumps to the
old inner loop latch which becomes the new outer loop latch after
interchange.
Reviewed By: bmahjour
Differential Revision: https://reviews.llvm.org/D98475
This is yet another attempt to fix tightlyNested().
Add checks in tightlyNested() for the inner loop exit block,
such that 1) if there is control-flow divergence in between the inner
loop exit block and the outer loop latch, or 2) if the inner loop exit
block contains unsafe instructions, tightlyNested() returns false.
The reasoning behind is that after interchange, the original inner loop
exit block, which was part of the outer loop, would be put into the new
inner loop, and will be executed different number of times before and
after interchange. Thus it should be dealt with appropriately.
Reviewed By: Whitney
Differential Revision: https://reviews.llvm.org/D98263
The check `tightlyNested()` in `LoopInterchange` is similar to the one in `LoopNest`.
In fact, the former misses some cases where loop-interchange is not feasible and results in incorrect behaviour.
Replacing it with the much robust version provided by `LoopNest` reduces code duplications and fixes https://bugs.llvm.org/show_bug.cgi?id=48113.
`LoopInterchange` has a weaker definition of tightly or perfectly nesting-ness than the one implemented in `LoopNest::arePerfectlyNested()`.
Therefore, `tightlyNested()` is instead implemented with `LoopNest::checkLoopsStructure` and additional checks for unsafe instructions.
Reviewed By: Whitney
Differential Revision: https://reviews.llvm.org/D97290
This is the preliminary patch of converting `LoopInterchange` pass to a loop-nest pass and has no intended functional change.
Changes that are not loop-nest related are split to D96650.
Reviewed By: Whitney
Differential Revision: https://reviews.llvm.org/D96644
This is a split patch of D96644.
Explicitly pass both `InnerLoop` and `OuterLoop` to function `processLoop` to remove the need to swap elements in loop list and allow making loop list an `ArrayRef`.
Also, fix inconsistent spellings of `OuterLoopId` and `Inner Loop Id` in debug log.
Reviewed By: fhahn
Differential Revision: https://reviews.llvm.org/D96650
In LoopInterchange, `findInnerReductionPhi()` looks for reduction
variables, which cannot be constants. Update it to return early in that
case.
This also addresses a blocker for removing use-lists from ConstantData,
whose users could be spread across arbitrary modules in the same
LLVMContext.
Differential Revision: https://reviews.llvm.org/D94712
... so just ensure that we pass DomTreeUpdater it into it.
Fixes DomTree preservation for a large number of tests,
all of which are marked as such so that they do not regress.
Instructions defined in the original inner loop preheader may depend on
values defined in the outer loop header, but the inner loop header will
become the entry block in the loop nest. Move the instructions from the
preheader to the outer loop header, so we do not break dominance. We
also have to check for unsafe instructions in the preheader. If there
are no unsafe instructions, all instructions should be movable.
Currently we move all instructions except the terminator and rely on
LICM to hoist out invariant instructions later.
Fixes PR45743
Values defined in the outer loop header could be used in the inner loop
latch. In that case, we need to create LCSSA phis for them, because after
interchanging they will be defined in the new inner loop and used in the
new outer loop.
Summary:
Currently the dependence analysis in LLVM is unable to compute accurate
dependence vectors for multi-dimensional fixed size arrays.
This is mainly because the delinearization algorithm in scalar evolution
relies on parametric terms to be present in the access functions. In the
case of fixed size arrays such parametric terms are not present, but we
can use the indexes from GEP instructions to recover the subscripts for
each dimension of the arrays. This patch adds this ability under the
existing option `-da-disable-delinearization-checks`.
Authored By: bmahjour
Reviewer: Meinersbur, sebpop, fhahn, dmgreen, grosser, etiotto, bollu
Reviewed By: Meinersbur
Subscribers: hiraditya, arphaman, Whitney, ppc-slack, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D72178
The PHI node checks for inner loop exits are too permissive currently.
As indicated by an existing comment, we should only allow LCSSA PHI
nodes that are part of reductions or are only used outside of the loop
nest. We ensure this by checking the users of the LCSSA PHIs.
Specifically, it is not safe to use an exiting value from the inner loop in the latch of the outer
loop.
It also moves the inner loop exit check before the outer loop exit
check.
Fixes PR43473.
Reviewers: efriedma, mcrosier
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D68144
Currently the assertion in updateSuccessor is overly strict in some
cases and overly relaxed in other cases. For branches to the inner and
outer loop preheader it is too strict, because they can either be
unconditional branches or conditional branches with duplicate targets.
Both cases are fine and we can allow updating multiple successors.
On the other hand, we have to at least update one successor. This patch
adds such an assertion.
Currently we have limited support for outer loops with multiple basic
blocks after the inner loop exit. But the current checks for creating
PHIs for loop exit values only assumes the header and latches of the
outer loop. It is better to just skip incoming values defined in the
original inner loops. Those are handled earlier.
Reviewers: efriedma, mcrosier
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D70059
Currently we only rely on the induction increment to come before the
condition to ensure the required instructions get moved to the new
latch.
This patch duplicates and moves the required instructions to the
newly created latch. We move the condition to the end of the new block,
then process its operands. We stop at operands that are defined
outside the loop, or are the induction PHI.
We duplicate the instructions and update the uses in the moved
instructions, to ensure other users remain intact. See the added
test2 for such an example.
Reviewers: efriedma, mcrosier
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D67367
llvm-svn: 371595
The code to preserve LCSSA PHIs currently only properly supports
reduction PHIs and PHIs for values defined outside the latches.
This patch improves the LCSSA PHI handling to cover PHIs for values
defined in the latches.
Fixes PR41725.
Reviewers: efriedma, mcrosier, davide, jdoerfert
Reviewed By: jdoerfert
Differential Revision: https://reviews.llvm.org/D61576
llvm-svn: 361743
As it's causing some bot failures (and per request from kbarton).
This reverts commit r358543/ab70da07286e618016e78247e4a24fcb84077fda.
llvm-svn: 358546
This patch adds logic to detect reductions across the inner and outer
loop by following the incoming values of PHI nodes in the outer loop. If
the incoming values take part in a reduction in the inner loop or come
from outside the outer loop, we found a reduction spanning across inner
and outer loop.
With this change, ~10% more loops are interchanged in the LLVM
test-suite + SPEC2006.
Fixes https://bugs.llvm.org/show_bug.cgi?id=30472
Reviewers: mcrosier, efriedma, karthikthecool, davide, hfinkel, dmgreen
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D43245
llvm-svn: 346438
Inner-loop only reductions require additional checks to make sure they
form a load-phi-store cycle across inner and outer loop. Otherwise the
reduction value is not properly preserved. This patch disables
interchanging such loops for now, as it causes miscompiles in some
cases and it seems to apply only for a tiny amount of loops. Across the
test-suite, SPEC2000 and SPEC2006, 61 instead of 62 loops are
interchange with inner loop reduction support disabled. With
-loop-interchange-threshold=-1000, 3256 instead of 3267.
See the discussion and history of D53027 for an outline of how such legality
checks could look like.
Reviewers: efriedma, mcrosier, davide
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D53027
llvm-svn: 345877
This patch extends LoopInterchange to move LCSSA to the right place
after interchanging. This is required for LoopInterchange to become a
function pass.
An alternative to the manual moving of the PHIs, we could also re-form
the LCSSA phis for a set of interchanged loops, but that's more
expensive.
Reviewers: efriedma, mcrosier, davide
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D52154
llvm-svn: 343132
As preparation for LoopInterchange becoming a loop pass, it needs to
preserve ScalarEvolution. Even though interchanging should not change
the trip count of the loop, it modifies loop entry, latch and exit
blocks.
I added -verify-scev to some loop interchange tests, but the verification does
not catch problems caused by missing invalidation of SE in loop interchange, as
the trip counts themselves do not change. So there might be potential to
make the SE verification covering more stuff in the future.
Reviewers: mkazantsev, efriedma, karthikthecool
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D52026
llvm-svn: 342209
This enables da-delinearize in Dependence Analysis for delinearizing array
accesses into multiple dimensions. This can help to increase the power of
Dependence analysis on multi-dimensional arrays and prevent having to fall
back to the slower and less accurate MIV tests. It adds static checks on the
bounds of the arrays to ensure that one dimension doesn't overflow into
another, and brings our code in line with our tests.
Differential Revision: https://reviews.llvm.org/D45872
llvm-svn: 335217
In order to set breakpoints on labels and list source code around
labels, we need collect debug information for labels, i.e., label
name, the function label belong, line number in the file, and the
address label located. In order to keep these information in LLVM
IR and to allow backend to generate debug information correctly.
We create a new kind of metadata for labels, DILabel. The format
of DILabel is
!DILabel(scope: !1, name: "foo", file: !2, line: 3)
We hope to keep debug information as much as possible even the
code is optimized. So, we create a new kind of intrinsic for label
metadata to avoid the metadata is eliminated with basic block.
The intrinsic will keep existing if we keep it from optimized out.
The format of the intrinsic is
llvm.dbg.label(metadata !1)
It has only one argument, that is the DILabel metadata. The
intrinsic will follow the label immediately. Backend could get the
label metadata through the intrinsic's parameter.
We also create DIBuilder API for labels to be used by Frontend.
Frontend could use createLabel() to allocate DILabel objects, and use
insertLabel() to insert llvm.dbg.label intrinsic in LLVM IR.
Differential Revision: https://reviews.llvm.org/D45024
Patch by Hsiangkai Wang.
llvm-svn: 331841
We currently support LCSSA PHI nodes in the outer loop exit, if their
incoming values do not come from the outer loop latch or if the
outer loop latch has a single predecessor. In that case, the outer loop latch
will be executed only if the inner loop gets executed. If we have multiple
predecessors for the outer loop latch, it may be executed even if the inner
loop does not get executed.
This is a first step to support the case described in
https://bugs.llvm.org/show_bug.cgi?id=30472
Reviewers: efriedma, karthikthecool, mcrosier
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D43237
llvm-svn: 331037
This also means we have to check if the latch is the exiting block now,
as `transform` expects the latches to be the exiting blocks too.
https://bugs.llvm.org/show_bug.cgi?id=36586
Reviewers: efriedma, davide, karthikthecool
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D45279
llvm-svn: 330806
Congzhe Cao