This extends a similar pattern from D125500 and D127754.
If we know that operand 1 (RHS) of a subtract is itself a
non-overflowing subtract from operand 0 (LHS), then the
final/outer subtract is also non-overflowing:
https://alive2.llvm.org/ce/z/Bqan8v
InstCombine uses this analysis to trigger a narrowing
optimization, so that is what the first changed test shows.
The last test models a motivating case from issue #48013.
In that example, we determine 'nuw' on the first sub from
the urem, then we determine that the 2nd sub can be narrowed,
and that leads to eliminating both subtracts.
here are still several missing subtract narrowing optimizations
demonstrated in the tests above the diffs shown here - those
should be handled in InstCombine with another set of patches.
This extends a similar pattern from D125500.
If we know that operand 1 (RHS) of a subtract is itself a
non-overflowing subtract from operand 0 (LHS), then the
final/outer subtract is also non-overflowing:
https://alive2.llvm.org/ce/z/Bqan8v
InstCombine uses this analysis to trigger a narrowing
optimization, so that is what the first changed test shows.
The last test models the motivating case from issue #48013.
In that example, we determine 'nsw' on the first sub from
the srem, then we determine that the 2nd sub can be narrowed,
and that leads to eliminating both subtracts.
This works for unsigned sub too, but I left that out to keep
the patch minimal. If this looks ok, I will follow up with
that change. There are also several missing subtract narrowing
optimizations demonstrated in the tests above the diffs shown
here - those should be handled in InstCombine with another set
of patches.
Differential Revision: https://reviews.llvm.org/D127754
I fixed some poison-safety violations on related patterns in InstCombine
and noticed that we missed adding nsw/nuw on them, so this adds clauses
to the underlying analysis for that.
We need the undef input restriction to make this safe according to Alive2:
https://alive2.llvm.org/ce/z/48g9K8
Differential Revision: https://reviews.llvm.org/D125500
Now that integer min/max intrinsics have good support in both
InstCombine and other passes, start canonicalizing SPF min/max
to intrinsic min/max.
Once this sticks, we can stop matching SPF min/max in various
places, and can remove hacks we have for preventing infinite loops
and breaking of SPF canonicalization.
Differential Revision: https://reviews.llvm.org/D98152
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 patch updates ConstantVector::getSplat to use poison instead
of undef when using insertelement/shufflevector to splat.
This follows on from D93793.
Differential Revision: https://reviews.llvm.org/D107751
This patch is an extension of D103421. It allows the InstCombiner to
generate the negated form of integer scalable-vector splats. It can
technically handle fixed-length vectors too but those are completely
covered by the preceding logic.
This enables extra combining opportunities for scalable vector types.
Reviewed By: RKSimon
Differential Revision: https://reviews.llvm.org/D103801
This patch extends the various "isXXX" functions of the `Constant` class
to include scalable-vector splats.
In several "isXXX" functions, code that was separately inspecting
`ConstantVector` and `ConstantDataVector` was unified to use
`getSplatValue`, which already includes support for said splats.
In the varous "isNotXXX" functions, code was added to check whether the
scalar splat value -- if any -- satisfies the predicate.
An extra fix for `isNotMinSignedValue` was included, as it previously
crashed when passed a scalable-vector type because it unconditionally
cast to `FixedVectorType`
These changes address numerous missed optimizations, a compiler crash
mentioned above and -- perhaps most egregiously -- an infinite loop in
InstCombine due to the compiler breaking canonical form when it failed
to pick up on a splat in a select instruction.
Test cases have been added to cover as many of these functions as
possible, though existing coverage is slim; it doesn't appear that there
are any in-tree uses of `Constant::isNegativeZeroValue`, for example.
Reviewed By: RKSimon
Differential Revision: https://reviews.llvm.org/D103421
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.
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
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.
This was the most obvious regression in
f5df5cd5586ae9cfb2d9e53704dfc76f47aff149.f5df5cd5586ae9cfb2d9e53704dfc76f47aff149
We really don't want to do this if the original/outermost subtraction
isn't a negation, and therefore doesn't go away - just sinking negation
isn't a win. We are actually appear to be missing folds so hoist it.
https://rise4fun.com/Alive/tiVe
This reverts commit ac70b37a00
which reverted commit 8aeb2fe13a
because codegen tests got broken and i needed time to investigate.
This shows some regressions in tests, but they are all around GEP's,
so i'm not really sure how important those are.
https://rise4fun.com/Alive/1Gn
The -reassociate pass tends to transform this kind of pattern into
something that is worse for vectorization and codegen. See PR43953:
https://bugs.llvm.org/show_bug.cgi?id=43953
Follows-up the FP version of the same transform:
rGa0ce2338a083
While we can do that, it doesn't increase instruction count,
if the old `sub` sticks around then the transform is not only
not a unlikely win, but a likely regression, since we likely
now extended live range and use count of both of the `sub` operands,
as opposed to just the result of `sub`.
As Kostya Serebryany notes in post-commit review in
https://reviews.llvm.org/D68408#1998112
this indeed can degrade final assembly,
increase register pressure, and spilling.
This isn't what we want here,
so at least for now let's guard it with an use check.
Summary:
As we have discussed previously (e.g. in D63992 / D64090 / [[ https://bugs.llvm.org/show_bug.cgi?id=42457 | PR42457 ]]), `sub` instruction
can almost be considered non-canonical. While we do convert `sub %x, C` -> `add %x, -C`,
we sparsely do that for non-constants. But we should.
Here, i propose to interpret `sub %x, %y` as `add (sub 0, %y), %x` IFF the negation can be sinked into the `%y`
This has some potential to cause endless combine loops (either around PHI's, or if there are some opposite transforms).
For former there's `-instcombine-negator-max-depth` option to mitigate it, should this expose any such issues
For latter, if there are still any such opposing folds, we'd need to remove the colliding fold.
In any case, reproducers welcomed!
Reviewers: spatel, nikic, efriedma, xbolva00
Reviewed By: spatel
Subscribers: xbolva00, mgorny, hiraditya, reames, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D68408
Followup to D72978. This moves existing negation handling in
InstCombine into freelyNegateValue(), which make it composable.
In particular, root negations of div/zext/sext/ashr/lshr/sub can
now always be performed through a shl/trunc as well.
Differential Revision: https://reviews.llvm.org/D73288
Fixes https://bugs.llvm.org/show_bug.cgi?id=44529. We already have
a combine to sink a negation through a left-shift, but it currently
only works if the shift operand is negatable without creating any
instructions. This patch introduces freelyNegateValue() as a more
powerful extension of dyn_castNegVal(), which allows negating a
value as long as this doesn't end up increasing instruction count.
Specifically, this patch adds support for negating A-B to B-A.
This mechanism could in the future be extended to handle general
negation chains that a) start at a proper 0-X negation and b) only
require one operand to be freely negatable. This would end up as a
weaker form of D68408 aimed at the most obviously profitable subset
that eliminates a negation entirely.
Differential Revision: https://reviews.llvm.org/D72978
Summary:
Currently when computing a GEP offset using the function EmitGEPOffset
for the following instruction
getelementptr inbounds i32, i32* %p, i64 %offs
we get
mul nuw i64 %offs, 4
Unfortunately we cannot assume that unsigned wrapping won't happen
here because %offs is allowed to be negative.
Making such assumptions can lead to miscompilations: see the new test
test24_neg_offs in InstCombine/icmp.ll. Without the patch InstCombine
would generate the following comparison:
icmp eq i64 %offs, 4611686018427387902; 0x3ffffffffffffffe
Whereas the correct value to compare with is -2.
This patch replaces the NUW flag with NSW in the multiplication
instructions generated by EmitGEPOffset and adjusts the test suite.
https://bugs.llvm.org/show_bug.cgi?id=42699
Reviewers: chandlerc, craig.topper, ostannard, lebedev.ri, spatel, efriedma, nlopes, aqjune
Reviewed By: lebedev.ri
Subscribers: reames, lebedev.ri, hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D68342
llvm-svn: 375089
(X | C1) + C2 --> (X | C1) ^ C1 iff (C1 == -C2)
I verified the correctness using Alive:
https://rise4fun.com/Alive/YNV
This transform enables the following transform that already exists in
instcombine:
(X | Y) ^ Y --> X & ~Y
As a result, the full expected transform is:
(X | C1) + C2 --> X & ~C1 iff (C1 == -C2)
There already exists the transform in the sub case:
(X | Y) - Y --> X & ~Y
However this does not trigger in the case where Y is constant due to an earlier
transform:
X - (-C) --> X + C
With this new add fold, both the add and sub constant cases are handled.
Patch by Chris Dawson.
Differential Revision: https://reviews.llvm.org/D61517
llvm-svn: 360185
Sanjay Patel