This patch updates propgatesPoison to take a Use as argument and
propagatesPoison now returns true if the passed in operand causes the
user to yield poison if the operand is poison
This allows propagating poison if the condition of a select is poison.
This helps improve results for programUndefinedIfUndefOrPoison.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D111643
When creating SCEV expressions for ZExt, there's quite a bit of
reasoning done and in many places the reasoning in turn will try to
create new SCEVs for other ZExts.
This can have a huge compile-time impact. The attached test from #58402
takes an excessive amount of compile time; without the patch, the test
doesn't complete in 1500+ seconds, but with the patch it completes in 1
second.
To speed up this case, cache created ZExt expressions for given (SCEV, Ty) pairs.
Caching just ZExts is relatively straight-forward, but it might make
sense to extend it to other expressions in the future.
This has a slight positive impact on CTMark:
* O3: -0.03%
* ReleaseThinLTO: -0.03%
* ReleaseLTO-g: 0.00%
https://llvm-compile-time-tracker.com/compare.php?from=bf9de7464946c65f488fe86ea61bfdecb8c654c1&to=5ac0108553992fb3d58bc27b1518e8cf06658a32&stat=instructions:u
The patch also improves compile-time for some internal real-world workloads
where time spent in SCEV goes from ~300 seconds to ~3 seconds.
There are a few cases where computing & caching the result earlier may
return more pessimistic results, but the compile-time savings seem to
outweigh that.
Fixes#58402.
Reviewed By: mkazantsev
Differential Revision: https://reviews.llvm.org/D137505
Over the past day or so, i've took a large swing at our tests,
and reduced the number of tests that were still using the old syntax
from ~1800 to just 200.
Left to handle: (as it is seen in this patch)
* Transforms/LSR
* Transforms/CGP
* Transforms/TypePromotion
* Transforms/HardwareLoops
* Analysis/*
* some misc.
I think this is the right point to start actively refusing
to honor the old syntax, except for the old tests,
to prevent the old syntax from creeping back in.
Thus, let's add temporary default-off flag,
and if it is not passed refuse to accept old syntax.
The tests that still need porting are annotated with this flag.
Reviewed By: aeubanks
Differential Revision: https://reviews.llvm.org/D139647
If loop exits by condition like `A < B && X < Y`, and at least one of symbolic max
exit counts for these conditions is known, it can be used as estimate of symbolic
max exit count for whole branch. If both are known, then we can use their umin
as the estimate.
Differential Revision: https://reviews.llvm.org/D139403
Reviewed By: nikic
The global constant arguments could be in a different address space
than the first argument, so we have to add another overloaded argument.
This patch was originally made for CHERI LLVM (where globals can be in
address space 200), but it also appears to be useful for in-tree targets
as can be seen from the test diffs.
Differential Revision: https://reviews.llvm.org/D138722
The old code didn't bother to memoize blocks for which exact exit count is not
known. As result, in situation when exact isn't known but symbolic is known, this
info was lost. This patch fixes the situation: now we memoize when symbolic is
known (exact always implies symbolic, so this is a strict superset of what was before).
Differential Revision: https://reviews.llvm.org/D139515
Reviewed By: nikic
At the moment, getRangeRef may overflow the stack for very deeply nested
expressions.
This patch introduces a new getRangeRefIter function, which first builds
a worklist of N-ary expressions and phi nodes, followed by their
operands iteratively.
getRangeRef has been extended to also take a Depth argument and it
switches to use getRangeRefIter once the depth reaches a certain
threshold.
This ensures compile-time is not impacted in general. Note that
the iterative algorithm may lead to a slightly different evaluation
order, which could result in slightly worse ranges for cyclic phis.
https://llvm-compile-time-tracker.com/compare.php?from=23c3eb7cdf3478c9db86f6cb5115821a8f0f5f40&to=e0e09fa338e77e53242bfc846e1484350ad79773&stat=instructionsFixes#49579.
Reviewed By: mkazantsev
Differential Revision: https://reviews.llvm.org/D130728
This patch removes the bail out for signed predicates and non-positive
strides in howManyLessThans and updates computeMaxBECountForLT to return
SCEVCouldNotCompute for signed predicates with negative strides.
AFAICT bail-out was only added because computeMaxBECountForLT may not
handle negative signed strides correctly. Instead of not calling
computeMaxBECountForLT at all because we bail out earlier, we can
instead return SCEVCouldNotCompute in computeMaxBECountForLT.
The max backedge taken count will be computed as the max value of the
symbolic backedge taken count.
This improves precision in cases where we can compute symbolic backedge
taken counts and also fixes a crash.
Fixes#57818.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D135667
This removes creation of udiv/sdiv/urem/srem constant expressions,
in preparation for their removal. I've added a
ConstantExpr::isDesirableBinOp() predicate to determine whether
an expression should be created for a certain operator.
With this patch, div/rem expressions can still be created through
explicit IR/bitcode, forbidding them entirely will be the next step.
Differential Revision: https://reviews.llvm.org/D128820
Use poison instead of undef for SCEVUnkown of unreachable values.
This should be in line with the movement to replace undef with poison
when possible.
Suggested in D114650.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D128586
This reverts commit 1fbdbb559569641f6d509b569966901c8fb02b63.
All known issues surfaced by this patch should have been fixed now.
The fixes included fixing issues with SCEV expansion in LV and DA's
reliance on LCSSA phis.
Now that SimpleLoopUnswitch and other transforms no longer introduce
branch on poison, enable the -branch-on-poison-as-ub option by
default. The practical impact of this is mostly better flag
preservation in SCEV, and some freeze instructions no longer being
necessary.
Differential Revision: https://reviews.llvm.org/D125299
Also collect conditions from assume up-front in applyLoopGuards.
This allows re-using the logic to handle logical ANDs as assume
conditions.
It should should pave the road for a fix for #55645.
Fold %x umin_seq %y to %x if %x ule %y. This also subsumes the
special handling for constant operands, as if %y is constant this
folds to umin via implied poison reasoning, and if %x is constant
then either %x is not zero and it folds to umin, or it is known
zero, in which case it is ule anything.
Fold %x umin_seq %y to %x umin %y if %x cannot be zero. They only
differ in semantics for %x==0.
More generally %x *_seq %y folds to %x * %y if %x cannot be the
saturation fold (though currently we only have umin_seq).
Similar to how we convert logical and/or to bitwise and/or, we should
also convert umin_seq to umin based on implied poison reasoning. In
%x umin_seq %y, if %y being poison implies %x being poison, then we
don't need the sequential evaluation: Having %y contribute towards
the result will never make the result more poisonous. An important
corollary of this is that if %y is never poison, we also don't need
the sequential evaluation.
This avoids some of the regressions in D124910.
Differential Revision: https://reviews.llvm.org/D124921
