Op0 - umax(X, Op0) --> 0 - usub.sat(X, Op1)
I'm not sure if this is really an improvement in IR because
we probably have better recognition/analysis for min/max,
but this lines up with the fold we do for the icmp+select
idiom and removes another diff from D98152.
This is similar to the previous fold in the code that was
added with:
83c2fb9f66baa6a85130https://alive2.llvm.org/ce/z/5MrVB9
umax(X, Op1) - Op1 --> usub.sat(X, Op1)
https://alive2.llvm.org/ce/z/HpcGiJ
This happens in 2 or more steps with an icmp-select idiom
instead of an intrinsic. This is another step towards
canonicalization of the min/max intrinsics. See:
D98152
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
This is a translation of the existing code to handle the intrinsics
and another step towards D98152.
https://alive2.llvm.org/ce/z/jA7eBC
This pattern is already handled by underlying folds if there are
less uses, so the minimal tests in this case have extra uses.
The larger cmyk tests show the motivation - when combined with
other folds, we invert a larger sequence and eliminate 'not' ops.
This is a re-try of 3aa009cc87 which was reverted at
9577fac0fd because it caused an infinite loop.
For the extra test case, either re-ordering the transforms
or adding the extra clause to avoid sub-of-sub is enough
to prevent the infinite compile, but I'm doing both to be
safer.
Original commit message:
The motivation was to get min/max intrinsics to parity
with cmp+select idioms, but this unlocks a few more
folds because isFreeToInvert recognizes add/sub with
constants too.
In the min/max example, we have too many extra uses
for smaller folds to improve things, but this fold
is able to eliminate uses even though we can't reduce
the number of instructions.
The motivation was to get min/max intrinsics to parity
with cmp+select idioms, but this unlocks a few more
folds because isFreeToInvert recognizes add/sub with
constants too.
In the min/max example, we have too many extra uses
for smaller folds to improve things, but this fold
is able to eliminate uses even though we can't reduce
the number of instructions.
This may overlap partially with the reassociate pass,
but it seems simple enough that we should try it here
in InstCombine to enable other folds.
This shows up as an opportunity and potential regression
if we improve a subtract fold with 'not' ops to be more
general.
This pattern is visible in unrolled and vectorized loops.
Although the backend seems to be able to reassociate to
ideal form in the examples I looked at, we might as well
do that in IR for efficiency.
As discussed in the post-commit comments for:
3cdd05e519
It seems to be safe to propagate all flags from the final fneg
except for 'nsz' to the new select:
https://alive2.llvm.org/ce/z/J_APDc
nsz has unique FMF semantics: it is not poison, it is only
"insignificant" in the calculation according to the LangRef.
We need to adjust the FMF propagation on at least
one of these transforms as discussed in:
https://llvm.org/PR49654
...so this should make it easier to intersect flags.
This is one of the folds requested in:
https://llvm.org/PR39480https://alive2.llvm.org/ce/z/NczU3V
Note - this uses the normal FMF propagation logic
(flags transfer from the final value to new/intermediate ops).
It's not clear if this matches what Alive2 implements,
so we may want to adjust one or the other.
For example:
```
int src(unsigned int a, unsigned int b)
{
return __builtin_popcount(a << 16) + __builtin_popcount(b >> 16);
}
int tgt(unsigned int a, unsigned int b)
{
return __builtin_popcount((a << 16) | (b >> 16));
}
```
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D101210
All of the code that handles general constant here (other than the more
restrictive APInt-dealing code) expects that it is an immediate,
because otherwise we won't actually fold the constants, and increase
instruction count. And it isn't obvious why we'd be okay with
increasing the number of constant expressions,
those still will have to be run..
But after 2829094a8e
this could also cause endless combine loops.
So actually properly restrict this code to immediates.
This reverts commit a547b4e26b,
relanding commit 31d219d299,
which was reverted because there was a conflicting inverse transform,
which was causing an endless combine loop, which has now been adjusted.
Original commit message:
https://alive2.llvm.org/ce/z/67w-wQ
We prefer `add`s over `sub`, and this particular xform
allows further folds to happen:
Fixes https://bugs.llvm.org/show_bug.cgi?id=49858
I.e., if any/all of the consants is an expression, don't do it.
Since those constants won't reduce into an immediate,
but would be left as an constant expression, they could cause
endless combine loops after 31d219d299
added an inverse transformation.
We determined that the MSVC implementation of std::aligned* isn't suited
to our needs. It doesn't support 16 byte alignment or higher, and it
doesn't really guarantee 8 byte alignment. See
https://github.com/microsoft/STL/issues/1533
Also reverts "ADT: Change AlignedCharArrayUnion to an alias of std::aligned_union_t, NFC"
Also reverts "ADT: Remove AlignedCharArrayUnion, NFC" to bring back
AlignedCharArrayUnion.
This reverts commit 4d8bf870a8.
This reverts commit d10f9863a5.
This reverts commit 4b5dc150b9.
Prepare to delete `AlignedCharArrayUnion` by migrating its users over to
`std::aligned_union_t`.
I will delete `AlignedCharArrayUnion` and its tests in a follow-up
commit so that it's easier to revert in isolation in case some
downstream wants to keep using it.
Differential Revision: https://reviews.llvm.org/D92516
Update all the users of `AlignedCharArrayUnion` to stop peeking inside
(to look at `buffer`) so that a follow-up patch can replace it with an
alias to `std::aligned_union_t`.
This was reviewed as part of https://reviews.llvm.org/D92512, but I'm
splitting this bit out to commit first to reduce churn in case the
change to `AlignedCharArrayUnion` needs to be reverted for some
unexpected reason.
We need to preserve wrapping flags to allow better folds.
The cases with geps may be non-intuitive, but that appears to agree with Alive2:
https://alive2.llvm.org/ce/z/JQcqw7
We create 'nsw' ops independent from the original wrapping on the sub.
This is a retry of 324a53205. I cautiously reverted that at 6aa3fc4
because the rules about gep math were not clear. Since then, we
have added this line to LangRef for gep inbounds:
"The successive addition of offsets (without adding the base address)
does not wrap the pointer index type in a signed sense (nsw)."
See D90708 and post-commit comments on the revert patch for more details.
Handle the emission of the add in a single place, instead of three
different ones.
Don't emit an unnecessary add with zero to start with. It will get
dropped by InstCombine, but we may as well not create it in the
first place. This also means that InstCombine does not need to
specially handle this extra add.
This is conceptually NFC, but can affect worklist order etc.
There might be some demanded/known bits way to generalize this,
but I'm not seeing it right now.
This came up as a regression when I was looking at a different
demanded bits improvement.
https://rise4fun.com/Alive/5fl
Name: general
Pre: ((-1 << countTrailingZeros(C1)) & C2) == 0
%a1 = add i8 %x, C1
%a2 = and i8 %x, C2
%r = sub i8 %a1, %a2
=>
%r = and i8 %a1, ~C2
Name: test 1
%a1 = add i8 %x, 192
%a2 = and i8 %x, 10
%r = sub i8 %a1, %a2
=>
%r = and i8 %a1, -11
Name: test 2
%a1 = add i8 %x, -108
%a2 = and i8 %x, 3
%r = sub i8 %a1, %a2
=>
%r = and i8 %a1, -4
As shown in the affected test, we could increase instruction
count without this limitation. There's another test with extra
use that shows we still convert directly to a real "sext" if
possible.
There might be a better way to specify the pre-conditions,
but this is hopefully clearer than the way it was written:
https://rise4fun.com/Alive/Jhk3
Pre: C2 < 0 && isShiftedMask(C2) && (C1 == C1 & C2)
%a = and %x, C2
%r = add %a, C1
=>
%a2 = add %x, C1
%r = and %a2, C2
Pre-conditions seem to be optimal, but we don't need a use check
because we are only replacing an add with a sub.
https://rise4fun.com/Alive/hzN
Pre: (~C1 | C2 == -1) && isPowerOf2(C2+1)
%m = and i8 %x, C1
%f = xor i8 %m, C2
%r = add i8 %f, C3
=>
%r = sub i8 C2 + C3, %m
We do similar factorization folds in SimplifyUsingDistributiveLaws,
but that drops no-wrap properties. Propagating those optimally may
help solve:
https://llvm.org/PR47430
The propagation is all-or-nothing for these patterns: when all
3 incoming ops have nsw or nuw, the 2 new ops should have the
same no-wrap property:
https://alive2.llvm.org/ce/z/Dv8wsU
This also solves:
https://llvm.org/PR47584
This was supposed to be an NFC cleanup, but there's
a real logic difference (did not drop 'nsw') visible
in some tests in addition to an efficiency improvement.
This is because in the case where we have 2 GEPs,
the code was *always* swapping the operands and
negating the result. But if we have 2 GEPs, we
should *never* need swapping/negation AFAICT.
This is part of improving flags propagation noticed
with PR47430.
Sanjay Patel