The change to InstCombine in:
https://reviews.llvm.org/D29729
...exposes this missing fold in InstSimplify, so adding this
first to avoid a regression.
llvm-svn: 295573
A program may contain llvm.assume info that disagrees with other analysis.
This may be caused by UB in the program, so we must not crash because of that.
As noted in the code comments:
https://llvm.org/bugs/show_bug.cgi?id=31809
...we can do better, but this at least avoids the assert/crash in the bug report.
Differential Revision: https://reviews.llvm.org/D29395
llvm-svn: 293773
Summary:
Previously we assumed that the result of sqrt(x) always had 0 as its
sign bit. But sqrt(-0) == -0.
Reviewers: hfinkel, efriedma, sanjoy
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D28928
llvm-svn: 293115
There was an efficiency problem with how we processed @llvm.assume in
ValueTracking (and other places). The AssumptionCache tracked all of the
assumptions in a given function. In order to find assumptions relevant to
computing known bits, etc. we searched every assumption in the function. For
ValueTracking, that means that we did O(#assumes * #values) work in InstCombine
and other passes (with a constant factor that can be quite large because we'd
repeat this search at every level of recursion of the analysis).
Several of us discussed this situation at the last developers' meeting, and
this implements the discussed solution: Make the values that an assume might
affect operands of the assume itself. To avoid exposing this detail to
frontends and passes that need not worry about it, I've used the new
operand-bundle feature to add these extra call "operands" in a way that does
not affect the intrinsic's signature. I think this solution is relatively
clean. InstCombine adds these extra operands based on what ValueTracking, LVI,
etc. will need and then those passes need only search the users of the values
under consideration. This should fix the computational-complexity problem.
At this point, no passes depend on the AssumptionCache, and so I'll remove
that as a follow-up change.
Differential Revision: https://reviews.llvm.org/D27259
llvm-svn: 289755
As Eli noted in the post-commit thread for r288833, the use of
swapOperands() may not be allowed in InstSimplify, so I'm
removing those calls here pending further review.
The swap mutates the icmp, and there doesn't appear to be precedent
for instruction mutation in InstSimplify.
I didn't actually have any tests for those cases, so I'm adding
a few here.
llvm-svn: 288855
All of these (and a few more) are already handled by InstCombine,
but we shouldn't have to wait until then to simplify these because
they're cheap to deal with here in InstSimplify.
This is the 'and' sibling of the earlier 'or' patch:
https://reviews.llvm.org/rL288833
llvm-svn: 288841
All of these (and a few more) are already handled by InstCombine,
but we shouldn't have to wait until then to simplify these because
they're cheap to deal with here in InstSimplify.
llvm-svn: 288833
Summary:
Extends InstSimplify to handle both `x >=u x >> y` and `x >=u x udiv y`.
This is a folloup of rL258422 and
https://github.com/rust-lang/rust/pull/30917 where llvm failed to
optimize away the bounds checking in a binary search.
Patch by Arthur Silva!
Reviewers: sanjoy
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D25941
llvm-svn: 285228
0 - X --> X, if X is 0 or the minimum signed value
0 - X --> 0, if X is 0 or the minimum signed value and the sub is NSW
I noticed this pattern might be created in the backend after the change from D25485,
so we'll want to add a similar fold for the DAG.
The use of computeKnownBits in InstSimplify may be something to investigate if the
compile time of InstSimplify is noticeable. We could replace computeKnownBits with
specific pattern matchers or limit the recursion.
Differential Revision: https://reviews.llvm.org/D25785
llvm-svn: 284649
The constant folder didn't know how to always fold bitcasts of constant integer
vectors. In particular, it was unable to handle the case where a constant vector
had some undef elements, and the resulting (i.e. bitcasted) vector type had more
elements than the original vector type.
Example:
%cast = bitcast <2 x i64><i64 undef, i64 2> to <4 x i32>
On a little endian target, %cast could have been folded to:
<4 x i32><i32 undef, i32 undef, i32 2, i32 0>
This patch improves the folding logic by teaching how to correctly propagate
undef elements in the folded vector.
Differential Revision: https://reviews.llvm.org/D24301
llvm-svn: 281343
InstSimplify doesn't always know how to fold a bitcast of a constant vector.
In particular, the logic in InstSimplify doesn't know how to handle the case
where the constant vector in input contains some undef elements, and the
number of elements is smaller than the number of elements of the bitcast
vector type.
llvm-svn: 281332
This patch fixes a crash caused by an incorrect folding of an ordered comparison
between a packed floating point vector and a splat vector of NaN.
An ordered comparison between a vector and a constant vector of NaN, should
always be folded into a constant vector where each element is i1 false.
Since revision 266175, SimplifyFCmpInst folds the ordered fcmp into a scalar
'false'. Later on, this would cause an assertion failure, since the value type
of the folded value doesn't match the expected value type of the uses of the
original instruction: "Assertion failed: New->getType() == getType() &&
"replaceAllUses of value with new value of different type!".
This patch fixes the issue and adds a test case to the already existing test
InstSimplify/floating-point-compares.ll.
Differential Revision: https://reviews.llvm.org/D24143
llvm-svn: 280488
...because like the corresponding code, this is just too big to keep adding to.
And the next step is to add a vector version of each of these tests to show
missed folds.
Also, auto-generate CHECK lines and add comments for the tests that correspond to
the source code.
llvm-svn: 279530
I'm removing a misplaced pair of more specific folds from InstCombine in this patch as well,
so we know where those folds are happening in InstSimplify.
llvm-svn: 277738
ConstantExpr::getWithOperands does much of the hard work that
ConstantFoldInstOperandsImpl tries to do but more completely.
This lets us fold ExtractValue/InsertValue expressions.
llvm-svn: 277100
When folding an expression, we run ConstantFoldConstantExpression on
each operand of that expression.
However, ConstantFoldConstantExpression can fail and retur nullptr.
Previously, we would bail on further refining the expression.
Instead, use the original operand and see if we can refine a later
operand.
llvm-svn: 276959
rL245171 exposed a hole in InstSimplify that manifested in a strange way in PR28466:
https://llvm.org/bugs/show_bug.cgi?id=28466
It's possible to use trunc + icmp sgt/slt in place of an and + icmp eq/ne, so we need to
recognize that pattern to eliminate selects that are choosing between some value and some
bitmasked version of that value.
Note that there is significant room for improvement (refactoring) and enhancement (more
patterns, possibly in InstCombine rather than here).
Differential Revision: https://reviews.llvm.org/D22537
llvm-svn: 276341
Treat loads which clip before the start of a global initializer the same
way we treat clipping beyond the end of the initializer: use zeros.
llvm-svn: 275345
For functions which are known to return a specific argument, pointer-comparison
folding can look through the function calls as part of its analysis.
Differential Revision: http://reviews.llvm.org/D9387
llvm-svn: 275039
This is similar to the computeKnownBits improvement in rL268479.
There's probably more we can do for vector logic instructions, but
this should let us see non-splat constant masking ops that can
become vector selects instead of and/andn/or sequences.
Differential Revision: http://reviews.llvm.org/D21610
llvm-svn: 273459
By moving this transform to InstSimplify from InstCombine, we sidestep the problem/question
raised by PR27869:
https://llvm.org/bugs/show_bug.cgi?id=27869
...where InstCombine turns an icmp+zext into a shift causing us to miss the fold.
Credit to David Majnemer for a draft patch of the changes to InstructionSimplify.cpp.
Differential Revision: http://reviews.llvm.org/D21512
llvm-svn: 273200
Similar in spirit to D20497 :
If all elements of a constant vector are known non-zero, then we can say that the
whole vector is known non-zero.
It seems like we could extend this to FP scalar/vector too, but isKnownNonZero()
says it only works for integers and pointers for now.
Differential Revision: http://reviews.llvm.org/D20544
llvm-svn: 270562
Vector GEP with mixed (vector and scalar) indices failed on the InstSimplify Pass when all indices are constants.
Differential revision http://reviews.llvm.org/D20149
llvm-svn: 269590
Do simplifications common to all shift instructions based on the amount shifted:
1. If the shift amount is known larger than the bitwidth, the result is undefined.
2. If the valid bits of the shift amount are all known to be 0, it's a shift by zero, so the shift operand is the result.
Note that we could generalize the shift-by-zero transform into a shift-by-constant if all of the valid bits in the shift
amount are known, but that would have to be done in InstCombine rather than here because it would mean we need to create
a new shift instruction.
Differential Revision: http://reviews.llvm.org/D19874
llvm-svn: 269114
This intrinsic takes two arguments, ``%ptr`` and ``%offset``. It loads
a 32-bit value from the address ``%ptr + %offset``, adds ``%ptr`` to that
value and returns it. The constant folder specifically recognizes the form of
this intrinsic and the constant initializers it may load from; if a loaded
constant initializer is known to have the form ``i32 trunc(x - %ptr)``,
the intrinsic call is folded to ``x``.
LLVM provides that the calculation of such a constant initializer will
not overflow at link time under the medium code model if ``x`` is an
``unnamed_addr`` function. However, it does not provide this guarantee for
a constant initializer folded into a function body. This intrinsic can be
used to avoid the possibility of overflows when loading from such a constant.
Differential Revision: http://reviews.llvm.org/D18367
llvm-svn: 267223
No matter what value you OR in to A, the result of (or A, B) is going to be UGE A. When A and B are positive, it's SGE too. If A is negative, OR'ing a value into it can't make it positive, but can increase its value closer to -1, therefore (or A, B) is SGE A. Working through all possible combinations produces this truth table:
```
A is
+, -, +/-
F F F + B is
T F ? -
? F ? +/-
```
The related optimizations are flipping the 'slt' for 'sge' which always NOTs the result (if the result is known), and swapping the LHS and RHS while swapping the comparison predicate.
There are more idioms left to implement (aren't there always!) but I've stopped here because any more would risk becoming unreasonable for reviewers.
llvm-svn: 266939
I didn't notice any significant changes in the actual checks here;
all of these tests already used FileCheck, so a script can batch
update them in one shot.
This commit is just to show the value of automating this process:
We have uniform formatting as opposed to a mish-mash of check
structure that changes based on individual prefs and the current
fashion. This makes it simpler to update when we find a bug or
make an enhancement.
llvm-svn: 264457
The constant folding for sdiv and udiv has a big discrepancy between the
comments and the code, which looks like a typo. Currently, we're folding
X / undef pretty inconsistently:
0 / undef -> undef
C / undef -> 0
undef / undef -> 0
Whereas the comments state we do X / undef -> undef. The logic that
returns zero is actually commented as doing undef / X -> 0, despite that
the LHS isn't undef in many of the cases that hit it.
llvm-svn: 261813
Summary:
Added a test case just to make sure that isKnownNonZero() returns false
when we cannot guarantee that a ConstantExpr is a non-zero constant.
Reviewers: sanjoy, majnemer, mcrosier, nlewycky
Subscribers: nlewycky, mssimpso, mcrosier, llvm-commits
Differential Revision: http://reviews.llvm.org/D16908
llvm-svn: 260544
This commit extends the patterns recognised by InstSimplify to also handle (x >> y) <= x in the same way as (x /u y) <= x.
The missing optimisation was found investigating why LLVM did not optimise away bound checks in a binary search: https://github.com/rust-lang/rust/pull/30917
Patch by Andrea Canciani!
Differential Revision: http://reviews.llvm.org/D16402
llvm-svn: 258422
This patch removes the isOperatorNewLike predicate since it was only being used to establish a non-null return value and we have attributes specifically for that purpose with generic handling. To keep approximate the same behaviour for existing frontends, I added the various operator new like (i.e. instances of operator new) to InferFunctionAttrs. It's not really clear to me why this isn't handled in Clang, but I didn't want to break existing code and any subtle assumptions it might have.
Once this patch is in, I'm going to start separating the isAllocLike family of predicates. These appear to be being used for a mixture of things which should be more clearly separated and documented. Today, they're being used to indicate (at least) aliasing facts, CSE-ability, and default values from an allocation site.
Differential Revision: http://reviews.llvm.org/D15820
llvm-svn: 256787
Summary:
This change teaches isImpliedCondition to prove things like
(A | 15) < L ==> (A | 14) < L
if the low 4 bits of A are known to be zero.
Depends on D14391
Reviewers: majnemer, reames, hfinkel
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D14392
llvm-svn: 252673
This is a cleaned up version of a patch by John Regehr with permission. Originally found via the souper tool.
If we add an odd number to x, then bitwise-and the result with x, we know that the low bit of the result must be zero. Either it was zero in x originally, or the add cleared it in the temporary value. As a result, one of the two values anded together must have the bit cleared.
Differential Revision: http://reviews.llvm.org/D14315
llvm-svn: 252629
Summary:
Currently `isImpliedCondition` will optimize "I +_nuw C < L ==> I < L"
only if C is positive. This is an unnecessary restriction -- the
implication holds even if `C` is negative.
Reviewers: reames, majnemer
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D14369
llvm-svn: 252332
Summary:
This change adds a framework for adding more smarts to
`isImpliedCondition` around inequalities. Informally,
`isImpliedCondition` will now try to prove "A < B ==> C < D" by proving
"C <= A && B <= D", since then it follows "C <= A < B <= D".
While this change is in principle NFC, I could not think of a way to not
handle cases like "i +_nsw 1 < L ==> i < L +_nsw 1" (that ValueTracking
did not handle before) while keeping the change understandable. I've
added tests for these cases.
Reviewers: reames, majnemer, hfinkel
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D14368
llvm-svn: 252331
Follow on to http://reviews.llvm.org/D13074, implementing something pointed out by Sanjoy. His truth table from his comment on that bug summarizes things well:
LHS | RHS | LHS >=s RHS | LHS implies RHS
0 | 0 | 1 (0 >= 0) | 1
0 | 1 | 1 (0 >= -1) | 1
1 | 0 | 0 (-1 >= 0) | 0
1 | 1 | 1 (-1 >= -1) | 1
The key point is that an "i1 1" is the value "-1", not "1".
Differential Revision: http://reviews.llvm.org/D13756
llvm-svn: 251597
First, the motivation: LLVM currently does not realize that:
((2072 >> (L == 0)) >> 7) & 1 == 0
where L is some arbitrary value. Whether you right-shift 2072 by 7 or by 8, the
lowest-order bit is always zero. There are obviously several ways to go about
fixing this, but the generic solution pursued in this patch is to teach
computeKnownBits something about shifts by a non-constant amount. Previously,
we would give up completely on these. Instead, in cases where we know something
about the low-order bits of the shift-amount operand, we can combine (and
together) the associated restrictions for all shift amounts consistent with
that knowledge. As a further generalization, I refactored all of the logic for
all three kinds of shifts to have this capability. This works well in the above
case, for example, because the dynamic shift amount can only be 0 or 1, and
thus we can say a lot about the known bits of the result.
This brings us to the second part of this change: Even when we know all of the
bits of a value via computeKnownBits, nothing used to constant-fold the result.
This introduces the necessary code into InstCombine and InstSimplify. I've
added it into both because:
1. InstCombine won't automatically pick up the associated logic in
InstSimplify (InstCombine uses InstSimplify, but not via the API that
passes in the original instruction).
2. Putting the logic in InstCombine allows the resulting simplifications to become
part of the iterative worklist
3. Putting the logic in InstSimplify allows the resulting simplifications to be
used by everywhere else that calls SimplifyInstruction (inlining, unrolling,
and many others).
And this requires a small change to our definition of an ephemeral value so
that we don't break the rest case from r246696 (where the icmp feeding the
@llvm.assume, is also feeding a br). Under the old definition, the icmp would
not be considered ephemeral (because it is used by the br), but this causes the
assume to remove itself (in addition to simplifying the branch structure), and
it seems more-useful to prevent that from happening.
llvm-svn: 251146
This is a cleaned up patch from the one written by John Regehr based on the findings of the Souper superoptimizer.
When writing tests, I was surprised to find that instsimplify apparently doesn't know how to collapse bit test sequences based purely on known bits. This required me to split my tests across both instsimplify and instcombine.
Differential Revision: http://reviews.llvm.org/D13250
llvm-svn: 249453
As mentioned in the bug, I'd missed the presence of a getScalarType in the caller of the new implies method. As a result, when we ended up with a implication over two vectors, we'd trip an assert and crash.
Differential Revision: http://reviews.llvm.org/D13441
llvm-svn: 249442
This was split off of http://reviews.llvm.org/D13040 to make it easier to test the correctness of the implication logic. For the moment, this only handles a single easy case which shows up when eliminating and combining range checks. In the (near) future, I plan to extend this for other cases which show up in range checks, but I wanted to make those changes incrementally once the framework was in place.
At the moment, the implication logic will be used by three places. One in InstSimplify (this review) and two in SimplifyCFG (http://reviews.llvm.org/D13040 & http://reviews.llvm.org/D13070). Can anyone think of other locations this style of reasoning would make sense?
Differential Revision: http://reviews.llvm.org/D13074
llvm-svn: 248719
- Move tests only exercising instsimplify to instsimplify's apint-or.ll
- Actually test the CHECK lines in instsimplify's apint-or.ll
- Merge the remaining tests in apint-or1.ll and apint-or2.ll, use FileCheck
llvm-svn: 247045
Sanjay Patel