There's no reason to shrink a constant or simplify
an operand in 2 steps.
This matches what we currently do for 'add' (although that
seems like it should be altered to handle the commutative
case).
This is copying the code that was added for 'add' with D130075.
(That patch removed a fallthrough in the cases, but we can
probably still share at least some code again as a follow-up
cleanup, but I didn't want to risk it here.)
The reasoning is similar to the carry propagation for 'add':
if we don't demand low bits of the subtraction and the
subtrahend (aka RHS or operand 1) is known zero in those low
bits, then there can't be any borrowing required from the
higher bits of operand 0, so the low bits don't matter.
Also, the no-wrap flags can be propagated (and I think that
should be true for add too).
Here's an attempt to prove that in Alive2:
https://alive2.llvm.org/ce/z/xqh7Pa
(can add nsw or nuw to src and tgt, and it should still pass)
Differential Revision: https://reviews.llvm.org/D136788
This was originally part of D133788. There are no visible
regressions. All of the diffs show a large unsigned constant
becoming a small negative constant. This should be better
for analysis (and slightly less compile-time) and codegen.
This patch enables a multi-use demanded bits fold (motivated by issue #57576):
https://alive2.llvm.org/ce/z/DsZakh
This mimics transforms that we already do on the single-use path.
Originally, this patch did not include the last part to form a constant, but
that can be removed independently to reduce risk. It's not clear what the
effect of either change will be when viewed end-to-end.
This is expected to be neutral or a slight win for compile-time.
See the "add-demand2" series for experimental timing results:
https://llvm-compile-time-tracker.com/?config=NewPM-O3&stat=instructions&remote=rotateright
Differential Revision: https://reviews.llvm.org/D133788
Don't demand low order bits from the LHS of an Add if:
- they are not demanded in the result, and
- they are known to be zero in the RHS, so they can't possibly
overflow and affect higher bit positions
This is intended to avoid a regression from a future patch to change
the order of canonicalization of ADD and AND.
Differential Revision: https://reviews.llvm.org/D130075
If we don't demand low bits and it is valid to pre-shift a constant:
(C2 >> X) << C1 --> (C2 << C1) >> X
https://alive2.llvm.org/ce/z/_UzTMP
This is the reverse-order shift sibling to 82040d414b ( D127122 ).
It seems likely that we would want to add this to the SDAG version of
the code too to keep it on par with IR.
If we don't demand high bits (zeros) and it is valid to pre-shift a constant:
(C2 << X) >> C1 --> (C2 >> C1) << X
https://alive2.llvm.org/ce/z/P3dWDW
There are a variety of related patterns, but I haven't found a single solution
that gets all of the motivating examples - so pulling this piece out of
D126617 along with more tests.
We should also handle the case where we shift-right followed by shift-left,
but I'll make that a follow-on patch assuming this one is ok. It seems likely
that we would want to add this to the SDAG version of the code too to keep it
on par with IR.
Differential Revision: https://reviews.llvm.org/D127122
This is a lshr equivalent to D122340 - if we don't demand any of the additional sign bits introduced by the ashr, the lshr can be treated as an ashr and we can remove the shift entirely if we only demand already known sign bits.
Another step towards PR21929
https://alive2.llvm.org/ce/z/6f3kjq
Differential Revision: https://reviews.llvm.org/D123118
We already do this for SelectionDAG, but we're missing it here.
Noticed while re-triaging PR21929
Differential Revision: https://reviews.llvm.org/D122340
This should no longer be necessary now that we canonicalize to
intrinsics. This may not be entirely NFC in practice if worklist
order gets inverted and we perform demanded bits simplification
of a select user before the select is canonicalized.
This is a follow-up suggested in D119060.
Instead of checking each of the bottom 2 bits individually,
we can check them together and handle the possibility that
we demand both together.
https://alive2.llvm.org/ce/z/C2ihC2
Differential Revision: https://reviews.llvm.org/D119139
gep(x, undef) carries the provenance of x, so we can't replace it with any
pointer like undef.
This leaves room for improvement for the poison case, but that's currently
not possible as the demanded bits API doesn't distinguish between undef &
poison bits.
Fixes#44790
Stop using APInt constructors and methods that were soft-deprecated in
D109483. This fixes all the uses I found in llvm, except for the APInt
unit tests which should still test the deprecated methods.
Differential Revision: https://reviews.llvm.org/D110807
The first two tries at this were reverted because they caused an
infinite loop in instcombine.
That should be fixed after a series of patches that ended with
removing the faulty opposing transform:
3fabd98e5b
Original commit message:
(masked) trunc (lshr X, C) --> (masked) lshr (trunc X), C
Narrowing the shift should be better for analysis and can lead
to follow-on transforms as shown.
Attempt at a general proof in Alive2:
https://alive2.llvm.org/ce/z/tRnnSF
Here are a couple of the specific tests:
https://alive2.llvm.org/ce/z/bCnTp-https://alive2.llvm.org/ce/z/TfaHnb
Differential Revision: https://reviews.llvm.org/D110170
This reverts commit bb9333c350.
This exposes another existing bug that causes an infinite loop as shown in
D110170
...so reverting while I look at another fix.
This reverts commit 2f6b07316f.
This caused several bots to hit an infinite loop at stage 2,
so it needs to be reverted while figuring out how to fix that.
This renames the primary methods for creating a zero value to `getZero`
instead of `getNullValue` and renames predicates like `isAllOnesValue`
to simply `isAllOnes`. This achieves two things:
1) This starts standardizing predicates across the LLVM codebase,
following (in this case) ConstantInt. The word "Value" doesn't
convey anything of merit, and is missing in some of the other things.
2) Calling an integer "null" doesn't make any sense. The original sin
here is mine and I've regretted it for years. This moves us to calling
it "zero" instead, which is correct!
APInt is widely used and I don't think anyone is keen to take massive source
breakage on anything so core, at least not all in one go. As such, this
doesn't actually delete any entrypoints, it "soft deprecates" them with a
comment.
Included in this patch are changes to a bunch of the codebase, but there are
more. We should normalize SelectionDAG and other APIs as well, which would
make the API change more mechanical.
Differential Revision: https://reviews.llvm.org/D109483
This is a direct translation of the select folds added with
D53033 / D53036 and another step towards canonicalization
using the intrinsics (see D98152).
This is a patch that replaces shufflevector and insertelement's placeholder value with poison.
Underlying motivation is to fix the semantics of shufflevector with undef mask to return poison instead
(D93818)
The consensus has been made in the late 2020 via mailing list as well as the thread in https://bugs.llvm.org/show_bug.cgi?id=44185 .
This patch is a simple syntactic change to the existing code, hence directly pushed as a commit.
As with other transforms in demanded bits, we must be careful not to
wrongly propagate nsw/nuw if we are reducing values leading up to the shift.
This bug was introduced with 1b24f35f84 and leads to the miscompile
shown in:
https://llvm.org/PR50341
As discussed in https://llvm.org/PR50096 , we could
convert the 'not' into a 'sub' and see the same
fold. That's because we already have another demanded
bits optimization for 'sub'.
We could add a related transform for
odd-number-of-type-bits, but that seems unlikely
to be practical.
https://alive2.llvm.org/ce/z/TWJZXr
Krzysztof Parzyszek