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
llvm-svn: 284818
This is to avoid inlining too many multiplication operands into a SCEV, which could
take exponential time in the worst case.
Reviewers: Sanjoy Das, Mehdi Amini, Michael Zolotukhin
Differential Revision: https://reviews.llvm.org/D25794
llvm-svn: 284784
In loops that look something like
i = n;
do {
...
} while(i++ < n+k);
where k is a constant, the maximum backedge count is k (in fact the backedge
count will be either 0 or k, depending on whether n+k wraps). More generally
for LHS < RHS if RHS-(LHS of first comparison) is a constant then the loop will
iterate either 0 or that constant number of times.
This allows for more loop unrolling with the recent upper bound loop unrolling
changes, and I'm working on a patch that will let loop unrolling additionally
make use of the loop being executed either 0 or k times (we need to retain the
loop comparison only on the first unrolled iteration).
Differential Revision: https://reviews.llvm.org/D25607
llvm-svn: 284465
Summary: The delinearization algorithm did not consider terms which had an extension without a multiply factor, i.e. a identify factor. We lose cases where size is char type where there will no multiply factor.
Reviewers: sanjoy, grosser
Subscribers: mzolotukhin, Eugene.Zelenko, llvm-commits, mssimpso, sanjoy, grosser
Differential Revision: https://reviews.llvm.org/D16492
llvm-svn: 284378
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.
llvm-svn: 284053
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
llvm-svn: 284044
This was first landed in rL283058 and subsequenlty reverted since a
change this depends on (rL283057) was buggy and had to be reverted.
llvm-svn: 283079
They've broken the sanitizer-bootstrap bots. Reverting while I investigate.
Original commit messages:
r283057: "[ConstantRange] Make getEquivalentICmp smarter"
r283058: "[SCEV] Rely on ConstantRange instead of custom logic; NFCI"
llvm-svn: 283062
Summary:
Instead of creating and destroying SCEVUnionPredicate instances (which
internally creates and destroys a DenseMap), use temporary SmallPtrSet
instances of remember the set of predicates that will get reified into a
SCEVUnionPredicate.
Reviewers: silviu.baranga, sbaranga
Subscribers: sanjoy, mcrosier, llvm-commits, mzolotukhin
Differential Revision: https://reviews.llvm.org/D25000
llvm-svn: 282606
I don't expect `PendingLoopPredicates` to have very many
elements (e.g. when -O3'ing the sqlite3 amalgamation,
`PendingLoopPredicates` has at most 3 elements). So now we use a
`SmallPtrSet` for it instead of the more heavyweight `DenseSet`.
llvm-svn: 282511
In a previous change I collapsed two different caches into one. When
doing that I noticed that ScalarEvolution's move constructor was not
moving those caches.
To keep the previous change simple, I've moved that bugfix into this
separate change.
llvm-svn: 282376
Both `loopHasNoSideEffects` and `loopHasNoAbnormalExits` involve walking
the loop and maintaining similar sorts of caches. This commit changes
SCEV to compute both the predicates via a single walk, and maintain a
single cache instead of two.
llvm-svn: 282375
This change simplifies a data structure optimization in the
`BackedgeTakenInfo` class for loops with exactly one computable exit.
I've sanity checked that this does not regress compile time performance,
using sqlite3's amalgamated build.
llvm-svn: 282365
Enhance SCEV to compute the trip count for some loops with unknown stride.
Patch by Pankaj Chawla
Differential Revision: https://reviews.llvm.org/D22377
llvm-svn: 281732
The fix for PR28705 will be committed consecutively.
In D12090, the ExprValueMap was added to reuse existing value during SCEV expansion.
However, const folding and sext/zext distribution can make the reuse still difficult.
A simplified case is: suppose we know S1 expands to V1 in ExprValueMap, and
S1 = S2 + C_a
S3 = S2 + C_b
where C_a and C_b are different SCEVConstants. Then we'd like to expand S3 as
V1 - C_a + C_b instead of expanding S2 literally. It is helpful when S2 is a
complex SCEV expr and S2 has no entry in ExprValueMap, which is usually caused
by the fact that S3 is generated from S1 after const folding.
In order to do that, we represent ExprValueMap as a mapping from SCEV to
ValueOffsetPair. We will save both S1->{V1, 0} and S2->{V1, C_a} into the
ExprValueMap when we create SCEV for V1. When S3 is expanded, it will first
expand S2 to V1 - C_a because of S2->{V1, C_a} in the map, then expand S3 to
V1 - C_a + C_b.
Differential Revision: https://reviews.llvm.org/D21313
llvm-svn: 278160
Besides a general consistently benefit, the extra layer of indirection
allows the mechanical part of https://reviews.llvm.org/D23256 that
requires touching every transformation and analysis to be factored out
cleanly.
Thanks to David for the suggestion.
llvm-svn: 278077
This change lets us prove things like
"{X,+,10} s< 5000" implies "{X+7,+,10} does not sign overflow"
It does this by replacing replacing getConstantDifference by
computeConstantDifference (which is smarter) in
isImpliedCondOperandsViaRanges.
llvm-svn: 276505
In D12090, the ExprValueMap was added to reuse existing value during SCEV expansion.
However, const folding and sext/zext distribution can make the reuse still difficult.
A simplified case is: suppose we know S1 expands to V1 in ExprValueMap, and
S1 = S2 + C_a
S3 = S2 + C_b
where C_a and C_b are different SCEVConstants. Then we'd like to expand S3 as
V1 - C_a + C_b instead of expanding S2 literally. It is helpful when S2 is a
complex SCEV expr and S2 has no entry in ExprValueMap, which is usually caused
by the fact that S3 is generated from S1 after const folding.
In order to do that, we represent ExprValueMap as a mapping from SCEV to
ValueOffsetPair. We will save both S1->{V1, 0} and S2->{V1, C_a} into the
ExprValueMap when we create SCEV for V1. When S3 is expanded, it will first
expand S2 to V1 - C_a because of S2->{V1, C_a} in the map, then expand S3 to
V1 - C_a + C_b.
Differential Revision: https://reviews.llvm.org/D21313
llvm-svn: 276136
When building SCEVs, if a function is known to return its argument, then we can
build the SCEV using the corresponding argument value.
Differential Revision: http://reviews.llvm.org/D9381
llvm-svn: 275037
Sanjoy Das