Summary:
Merge overflow computation for signed add,
appearing both in InstCombine and ValueTracking.
As part of the merge,
cleanup the interface for overflow checks in InstCombine.
Patch by Yoav Ben-Shalom.
Reviewers: craig.topper, majnemer
Reviewed By: craig.topper
Subscribers: takuto.ikuta, llvm-commits
Differential Revision: https://reviews.llvm.org/D32946
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@303029 91177308-0d34-0410-b5e6-96231b3b80d8
This patch adds min/max population count, leading/trailing zero/one bit counting methods.
The min methods return answers based on bits that are known without considering unknown bits. The max methods give answers taking into account the largest count that unknown bits could give.
Differential Revision: https://reviews.llvm.org/D32931
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@302925 91177308-0d34-0410-b5e6-96231b3b80d8
This patch uses KnownOnes of the input of ctlz/cttz to bound the value that can be returned from these intrinsics. This makes these intrinsics more similar to the handling for ctpop which already uses known bits to produce a similar bound.
Differential Revision: https://reviews.llvm.org/D32521
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@302444 91177308-0d34-0410-b5e6-96231b3b80d8
This introduces a new interface for computeKnownBits that returns the KnownBits object instead of requiring it to be pre-constructed and passed in by reference.
This is a much more convenient interface as it doesn't require the caller to figure out the BitWidth to pre-construct the object. It's so convenient that I believe we can use this interface to remove the special ComputeSignBit flavor of computeKnownBits.
As a step towards that idea, this patch replaces all of the internal usages of ComputeSignBit with this new interface. As you can see from the patch there were a couple places where we called ComputeSignBit which really called computeKnownBits, and then called computeKnownBits again directly. I've reduced those places to only making one call to computeKnownBits. I bet there are probably external users that do it too.
A future patch will update the external users and remove the ComputeSignBit interface. I'll also working on moving more locations to the KnownBits returning interface for computeKnownBits.
Differential Revision: https://reviews.llvm.org/D32848
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@302437 91177308-0d34-0410-b5e6-96231b3b80d8
I don't believe its possible to have non-zero values here since DataLayout became required. The APInt constructor inside of the KnownBits object will assert if this ever happens.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@302089 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
programUndefinedIfPoison makes more sense, given what the function
does; and I'm about to add a function with a name similar to
isKnownNotFullPoison (so do the rename to avoid confusion).
Reviewers: broune, majnemer, bjarke.roune
Reviewed By: broune
Subscribers: mcrosier, llvm-commits, mzolotukhin
Differential Revision: https://reviews.llvm.org/D30444
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301776 91177308-0d34-0410-b5e6-96231b3b80d8
Summary: This patch adds isNegative, isNonNegative for querying whether the sign bit is known. It also adds makeNegative and makeNonNegative for controlling the sign bit.
Reviewers: RKSimon, spatel, davide
Reviewed By: RKSimon
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D32651
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301747 91177308-0d34-0410-b5e6-96231b3b80d8
This patch introduces a new KnownBits struct that wraps the two APInt used by computeKnownBits. This allows us to treat them as more of a unit.
Initially I've just altered the signatures of computeKnownBits and InstCombine's simplifyDemandedBits to pass a KnownBits reference instead of two separate APInt references. I'll do similar to the SelectionDAG version of computeKnownBits/simplifyDemandedBits as a separate patch.
I've added a constructor that allows initializing both APInts to the same bit width with a starting value of 0. This reduces the repeated pattern of initializing both APInts. Once place default constructed the APInts so I added a default constructor for those cases.
Going forward I would like to add more methods that will work on the pairs. For example trunc, zext, and sext occur on both APInts together in several places. We should probably add a clear method that can be used to clear both pieces. Maybe a method to check for conflicting information. A method to return (Zero|One) so we don't write it out everywhere. Maybe a method for (Zero|One).isAllOnesValue() to determine if all bits are known. I'm sure there are many other methods we can come up with.
Differential Revision: https://reviews.llvm.org/D32376
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301432 91177308-0d34-0410-b5e6-96231b3b80d8
This patch uses various APInt methods to reduce temporary APInt creation.
This should be all of the unrelated cleanups that got buried in D32376(creating a KnownBits struct) as well as some pointed out by Simon during the review of that. Plus a few improvements to use counting instead of masking.
I've left out any places where we do something like (KnownZero & KnownOne) != 0 as I plan to add a helper method to KnownBits to ask that question and didn't want to thrash that code an additional time.
Differential Revision: https://reviews.llvm.org/D32495
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301338 91177308-0d34-0410-b5e6-96231b3b80d8
This is a pre-commit for a patch I'm working on to turn KnownZero/One into a struct. Once I do that the type here will be less obvious.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301324 91177308-0d34-0410-b5e6-96231b3b80d8
This is a pre-commit for a patch that I'm working on to merge KnownZero/KnownOne into a KnownBits struct which would have had to touch this line.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301323 91177308-0d34-0410-b5e6-96231b3b80d8
getSignBit is a static function that creates an APInt with only the sign bit set. getSignMask seems like a better name to convey its functionality. In fact several places use it and then store in an APInt named SignMask.
Differential Revision: https://reviews.llvm.org/D32108
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300856 91177308-0d34-0410-b5e6-96231b3b80d8
This is preparation for a clang change to improve the [[nodiscard]] warning to not be ignored on methods that return a class marked [[nodiscard]] that are defined in the class itself. See D32207.
We should consider adding wrapper methods to APInt that return the overflow flag directly and discard the APInt result. This would eliminate the void casts and the need to create a bool before the call to pass to the out param.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300758 91177308-0d34-0410-b5e6-96231b3b80d8
This patch uses lshrInPlace to replace code where the object that lshr is called on is being overwritten with the result.
This adds an lshrInPlace(const APInt &) version as well.
Differential Revision: https://reviews.llvm.org/D32155
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300566 91177308-0d34-0410-b5e6-96231b3b80d8
This makes statements like KnownZero.isNegative() (which means the value we're tracking is positive) less confusing.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300457 91177308-0d34-0410-b5e6-96231b3b80d8
If we already called computeKnownBits for the RHS being a constant power of 2, we've already computed everything we can and should just stop. I think previously we would still recurse if we had determined the result was negative or had not determined the sign bit at all.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300432 91177308-0d34-0410-b5e6-96231b3b80d8
The APInt was created from an 'unsigned' and we just wanted to know how many bits the value needed to represent it. We can just use Log2_32 from MathExtras.h to get the info.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300309 91177308-0d34-0410-b5e6-96231b3b80d8
We call it unconditionally on the operands of the select. Then decide if its a min/max and call it on the min/max operands or on the select operands again. Either of those second calls will overwrite the results of the initial call so we can just delete the first call.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300256 91177308-0d34-0410-b5e6-96231b3b80d8
Previously it tried to call SimplifyInstruction which doesn't know anything about alloca so defers to constant folding which also doesn't do anything with alloca. This results in wasted cycles making calls that won't do anything. Given the frequency with which this function is called this time adds up.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300118 91177308-0d34-0410-b5e6-96231b3b80d8
SimplifyDemandedUseBits for Add/Sub already recursed down LHS and RHS for simplifying bits. If that didn't provide any simplifications we fall back to calling computeKnownBits which will recurse again. Instead just take the known bits for LHS and RHS we already have and call into a new function in ValueTracking that can calculate the known bits given the LHS/RHS bits.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298711 91177308-0d34-0410-b5e6-96231b3b80d8
The code assigned to KnownZero, but later code unconditionally assigned over it. I'm pretty sure the later code can handle the same cases and more equally well.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298190 91177308-0d34-0410-b5e6-96231b3b80d8
If it is possible for the RHS of a shift operation to be greater than or equal
to the bit-width, then the result might be undef, and we can't report any known
bits.
In some cases, this was allowing a transformation in instcombine which widened
an undef value from i1 to i32, increasing the range of values that a function
could return.
Differential revision: https://reviews.llvm.org/D30781
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297724 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
Previously we used to return a bogus result, 0, for IR like `ashr %val,
-1`.
I've also added an assert checking that `ComputeNumSignBits` at least
returns 1. That assert found an already checked in test case where we
were returning a bad result for `ashr %val, -1`.
Fixes PR32045.
Reviewers: spatel, majnemer
Reviewed By: spatel, majnemer
Subscribers: efriedma, mcrosier, llvm-commits
Differential Revision: https://reviews.llvm.org/D30311
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296273 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
Motivation: fix PR31181 without regression (the actual fix is still in
progress). However, the actual content of PR31181 is not relevant
here.
This change makes poison propagation more aggressive in the following
cases:
1. poision * Val == poison, for any Val. In particular, this changes
existing intentional and documented behavior in these two cases:
a. Val is 0
b. Val is 2^k * N
2. poison << Val == poison, for any Val
3. getelementptr is poison if any input is poison
I think all of these are justified (and are axiomatically true in the
new poison / undef model):
1a: we need poison * 0 to be poison to allow transforms like these:
A * (B + C) ==> A * B + A * C
If poison * 0 were 0 then the above transform could not be allowed
since e.g. we could have A = poison, B = 1, C = -1, making the LHS
poison * (1 + -1) = poison * 0 = 0
and the RHS
poison * 1 + poison * -1 = poison + poison = poison
1b: we need e.g. poison * 4 to be poison since we want to allow
A * 4 ==> A + A + A + A
If poison * 4 were a value with all of their bits poison except the
last four; then we'd not be able to do this transform since then if A
were poison the LHS would only be "partially" poison while the RHS
would be "full" poison.
2: Same reasoning as (1b), we'd like have the following kinds
transforms be legal:
A << 1 ==> A + A
Reviewers: majnemer, efriedma
Subscribers: mcrosier, llvm-commits
Differential Revision: https://reviews.llvm.org/D30185
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@295809 91177308-0d34-0410-b5e6-96231b3b80d8
