The 'and (sext (ashr X, ShiftC)), C' --> 'lshr (sext X), ShiftC'
transformation would access out of bounds bits in APInt::getLowBitsSet
if the shift count was larger than X's bit width or if it was negative.
Fixes#56424
(-(X & 1)) & Y --> (X & 1) == 0 ? 0 : Y
https://alive2.llvm.org/ce/z/rhpH3i
This is noted as a missing IR canonicalization in issue #55618.
We already managed to fix codegen to the expected form.
When the mask is a power-of-2 constant and op0 is a shifted-power-of-2
constant, test if the shift amount equals the offset bit index:
(ShiftC << X) & C --> X == (log2(C) - log2(ShiftC)) ? C : 0
(ShiftC >> X) & C --> X == (log2(ShiftC) - log2(C)) ? C : 0
This is an alternate to D127610 with a more general pattern.
We match only shift+and instead of the trailing xor, so we see a few
more tests diffs. I think we discussed this initially in D126617.
Here are proofs for shifts in both directions:
https://alive2.llvm.org/ce/z/CFrLs4
The test diffs look equal or better for IR, and this makes the
patterns more uniform in IR. The backend can partially invert this
in both cases if that is profitable. It is not trivially reversible,
however, so if we find perf regressions that are not easy to undo,
then we may want to revert this.
Differential Revision: https://reviews.llvm.org/D127801
This shows narrowing improvements on the logic tests
(transforms recently added with e247b0e5c9).
This is not a complete fix. That would require adding
folds to visitOr/visitXor. But it enables the expected
transforms for the basic patterns in the affected tests.
The 1st try ( afa192cfb6 ) was reverted because it could
cause an infinite loop with constant expressions.
A test for that and an extra condition to enable the transform
are added now. I also added code comments to better describe
the transform and the existing, related transform.
Original commit message:
https://alive2.llvm.org/ce/z/hRy3rE
As shown in D123408, we can produce this pattern when moving
casts around, and we already have a related fold for a binop
with a constant operand.
https://alive2.llvm.org/ce/z/hRy3rE
As shown in D123408, we can produce this pattern when moving
cast around, and we already have a related fold for a binop
with a constant operand.
Clang-format InstructionSimplify and convert all "FunctionName"s to
"functionName". This patch does touch a lot of files but gets done with
the cleanup of InstructionSimplify in one commit.
This is the alternative to the less invasive clang-format only patch: D126783
Reviewed By: spatel, rengolin
Differential Revision: https://reviews.llvm.org/D126889
The patch simplifies some of the patterns as below
(A | (B & C0)) | (B & C1) -> A | (B & C0|C1)
((B & C0) | A) | (B & C1) -> (B & C0|C1) | A
In some scenarios like byte reverse on half word, we can see this pattern multiple times and this conversion can optimize these patterns.
Additionally this commit fixes the issue reported with the test case.
int f(int a, int b) {
int c = ((unsigned char)(a >> 23) & 925);
if (a)
c = (a >> 23 & b) | ((unsigned char)(a >> 23) & 925) | (b >> 23 & 157);
return c;
}
The previous revision/commit did not check one-use of an intermediate value that this transform re-uses.
When that value has another use, an existing transform will try to invert the transform here.
By adding one-use checks, we avoid the infinite loops seen with the earlier commit.
Differential Revision: https://reviews.llvm.org/D124119
This reverts commit ec4adf1f6c. The commit causes
clang to hang on a certain input:
```
$ cat q.cc
int f(int a, int b) {
int c = ((unsigned char)(a >> 23) & 925);
if (a)
c = (a >> 23 & b) | ((unsigned char)(a >> 23) & 925) | (b >> 23 & 157);
return c;
}
$ time ./clang-15-10515 --target=x86_64--linux-gnu -O1 -c q.cc
^C
real 0m45.072s
user 0m0.025s
sys 0m0.099s
```
Most of the folds implemented in this function work fine with
logical operations. We only need to be careful for the cases that
work on non-constant masks, where the RHS operand shouldn't be
poison.
This is a conservative implementation that bails out of illegal
transforms, but we could also change these to insert freeze instead.
Similarly to a change recently done for fcmps, add a flag that
indicates whether the and/or is logical to foldAndOrOfICmps, and
reuse the function when folding logical and/or.
We were already calling some parts of it, but this gives us a
clearer indication of which parts may need poison-safe variants,
and would also allow to fold combinations of bitwise and logical
and/or.
This change should be close to NFC, because all folds this enables
were either already called previously, or can make use of implied
poison reasoning.
The patch simplifies some of the patterns as below
(A | (B & C0)) | (B & C1) -> A | (B & C0|C1)
((B & C0) | A) | (B & C1) -> (B & C0|C1) | A
In some scenarios like byte reverse on half word, we can see this pattern multiple times and this conversion can optimize these patterns.
Differential Revision: https://reviews.llvm.org/D124119
D113035 enhanced the matching of bitwise selects from vector types. This
change unfortunately introduced crashes as it tries to cast scalable
vector types to integers.
Reviewed By: spatel
Differential Revision: https://reviews.llvm.org/D124997
This is an edge-case where we don't convert to bitwise and/or based
on implies poison reasoning, so explicitly try to perform the fold
in logical form. The transform itself is poison-safe, as both icmps
are based on the same value and any nowrap flags are discarded as
part of the fold (https://alive2.llvm.org/ce/z/aCwC8b for the used
example).
This fold handles a special subset of foldAndOrOfICmpsUsingRanges(),
use the more generic implementation instead.
The result can differ if a representation using a range comparison
is possible, in which case that is preferred over masking. There is
a canonicalization opportunity here.
This is the de Morgan conjugated variant of the existing fold for
ors. Implement this by switching the range code to always work
on ors and perform invert operands at the start and end. This makes
reasoning easier and makes the extension more obviosuly correct.
We can express this fold more naturally when working on the constant
range implementation. This change is not entirely NFC, because the
code now also handles cases that don't match the precise pattern
this previously looked for, e.g. we can omit an add on one of the
ranges.
Folds are supposed to always be added in conjugated pairs for and
and or. Merge the two functions to make folds for which this is
currently not the case more obvious.
1d90e53044 switch this code to store
the predicates and operands in variables, but retained a
swapOperands() call here. Thus the commuted cases were no longer
folded. Additionally, as the change was not reported, the next
InstCombine iteration would not pick it up either.
These two are equivalent,
and i *think* the `and` form is more-ish canonical.
General proof: https://alive2.llvm.org/ce/z/RrF5s6
If constant on the (outer) `xor` is an `undef`,
the whole lane is dead: https://alive2.llvm.org/ce/z/mu4Sh2
However, if the constant on the (inner) `or` is an `undef`,
we must sanitize it first: https://alive2.llvm.org/ce/z/MHYJL7
I guess, producing a zero `and`-mask is optimal in that case.
alive-tv is happy about the entirety of `xor-of-or.ll`.
If we have a logical and/or in select form and the true/false operand
is an fcmp with poison generating FMF, we won't be able to fold it
to an and/or instruction. This prevents us from optimizing the case
where it is a logical operation of two fcmps with identical operands.
This patch adds explicit checks for this case that doesn't rely on
converting to and/or to do the optimization. It reuses the existing
foldLogicOfFCmps, but adds a new flag to disable the other combine
that is inside that function.
FMF flags from the two FCmps are intersected using the logic added in
D121243. The FIXME has been updated to indicate that we can only use
a union for the non-select form.
This allows us to optimize cases like this from compare-fp-3.c in the
gcc torture suite with fast math.
void
test1 (float x, float y)
{
if ((x==y) && (x!=y))
link_error0();
}
Reviewed By: spatel
Differential Revision: https://reviews.llvm.org/D121323
This patch intersects the fast math flags from the two fcmps instead
of dropping them.
I poked at this a bunch with Alive2 for nnan and ninf flags and it seemed
to check out. With the other flags it told me "Couldn't prove the
correctness of the transformation". Not sure if I should just preserve
nnan and ninf?
Reviewed By: spatel, lebedev.ri
Differential Revision: https://reviews.llvm.org/D121243
The similar getICmpCode and getPredForICmpCode are already there.
This moves FP for consistency.
I think InstCombine is currently the only user of both.
Reviewed By: RKSimon
Differential Revision: https://reviews.llvm.org/D120754
Instead of passing an InstCmpInt * and a bool just pass the predicate
from the caller.
I'm considering moving the similar FCmp functions from InstCombine
over here and this makes the interface consistent with what is used
for FCmp.
Reviewed By: RKSimon
Differential Revision: https://reviews.llvm.org/D120609
While this might be marginally more precise, we generally don't
bother with this in InstCombine, and let the IRBuilder assign the
debug location. I don't see why this one fold, out of the thousands
done in InstCombine, should be treated specially.
This is an alternate version of D115914 that handles/tests all binary opcodes.
I suspect that we don't see these patterns too often because -simplifycfg
would convert the minimal cases into selects rather than leave them in phi form
(note: instcombine has logic holes for combining the select patterns too though,
so that's another potential patch).
We only create a new binop in a predecessor that unconditionally branches to
the final block.
https://alive2.llvm.org/ce/z/C57M2Fhttps://alive2.llvm.org/ce/z/WHwAoU (not safe to speculate an sdiv for example)
https://alive2.llvm.org/ce/z/rdVUvW (but it is ok on this path)
Differential Revision: https://reviews.llvm.org/D117110
Chenbing Zheng