What we want to know here is whether we're already using this value
for the loop condition, so make the query about that. We can extend
this to a more general "based-on" relationship, rather than a direct
icmp use later.
llvm-svn: 364715
The whole indvars pass works on loops in simplified form, so there
is always a unique latch. Convert the condition into an assertion
in needsLFTR (though we also assert this in later LFTR functions).
Additionally update the comment on getLoopTest() now that we are
dealing with multiple exits.
llvm-svn: 364713
Fixes https://bugs.llvm.org/show_bug.cgi?id=41998. Usually when we
have a truncated exit count we'll truncate the IV when comparing
against the limit, in which case exit count overflow in post-inc
form doesn't matter. However, for pointer IVs we don't do that, so
we have to be careful about incrementing the IV in the wide type.
I'm fixing this by removing the IVCount variable (which was
ExitCount or ExitCount+1) and replacing it with a UsePostInc flag,
and then moving the actual limit adjustment to the individual cases
(which are: pointer IV where we add to the wide type, integer IV
where we add to the narrow type, and constant integer IV where we
add to the wide type).
Differential Revision: https://reviews.llvm.org/D63686
llvm-svn: 364709
This allows later passes (in particular InstCombine) to optimize more
cases.
One that's important to us is `memcmp(p, q, constant) < 0` and memcmp(p, q, constant) > 0.
llvm-svn: 364412
Inference of nowrap flags in CVP has been disabled, because it
triggered a bug in LFTR (https://bugs.llvm.org/show_bug.cgi?id=31181).
This issue has been fixed in D60935, so we should be able to reenable
nowrap flag inference now.
Differential Revision: https://reviews.llvm.org/D62776
llvm-svn: 364228
In rL364135, I taught IndVars to fold exiting branches in loops with a zero backedge taken count (i.e. loops that only run one iteration). This extends that to eliminate the dead comparison left around.
llvm-svn: 364155
This turned out to be surprisingly effective. I was originally doing this just for completeness sake, but it seems like there are a lot of cases where SCEV's exit count reasoning is stronger than it's isKnownPredicate reasoning.
Once this is in, I'm thinking about trying to build on the same infrastructure to eliminate provably untaken checks. There may be something generally interesting here.
Differential Revision: https://reviews.llvm.org/D63618
llvm-svn: 364135
Summary:
The motivation for this was to propagate fast-math flags like nnan and
ninf on vector floating point operations to the corresponding scalar
operations to take advantage of follow-on optimizations. But I think
the same argument applies to all of our IR flags: if they apply to the
vector operation then they also apply to all the individual scalar
operations, and they might enable follow-on optimizations.
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D63593
llvm-svn: 364051
Also, add a FIXME for the unsafe transform on a unary FNeg. A unary FNeg can only be transformed to a FMul by -1.0 when the nnan flag is present. The unary FNeg project is a WIP, so the unsafe transformation is acceptable until that work is complete.
The bogus assert with introduced in D63445.
llvm-svn: 363998
Summary:
The getClobberingMemoryAccess API checks for clobbering accesses in a loop by walking the backedge. This may check if a memory access is being
clobbered by the loop in a previous iteration, depending how smart AA got over the course of the updates in MemorySSA (it does not occur when built from scratch).
If no clobbering access is found inside the loop, it will optimize to an access outside the loop. This however does not mean that access is safe to sink.
Given:
```
for i
load a[i]
store a[i]
```
The access corresponding to the load can be optimized to outside the loop, and the load can be hoisted. But it is incorrect to sink it.
In order to sink the load, we'd need to check no Def clobbers the Use in the same iteration. With this patch we currently restrict sinking to either
Defs not existing in the loop, or Defs preceding the load in the same block. An easy extension is to ensure the load (Use) post-dominates all Defs.
Caught by PR42294.
This issue also shed light on the converse problem: hoisting stores in this same scenario would be illegal. With this patch we restrict
hoisting of stores to the case when their corresponding Defs are dominating all Uses in the loop.
Reviewers: george.burgess.iv
Subscribers: jlebar, Prazek, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D63582
llvm-svn: 363982
I can't actually come up with a test case this triggers on without an out of tree change, but in theory, it's a bug in the recently added multiple exit LFTR support. The root issue is that an exiting block common to two loops can (in theory) have computable exit counts for both loops. Rewriting the exit of an inner loop in terms of the outer loops IV would cause the inner loop to either a) run forever, or b) terminate on the first iteration.
In practice, we appear to get lucky and not have the exit count computable for the outer loop, except when it's trivially zero. Given we bail on zero exit counts, we don't appear to ever trigger this. But I can't come up with a reason we *can't* compute an exit count for the outer loop on the common exiting block, so this may very well be triggering in some cases.
llvm-svn: 363964
Teach IndVarSimply's LinearFunctionTestReplace transform to handle multiple exit loops. LFTR does two key things 1) it rewrites (all) exit tests in terms of a common IV potentially eliminating one in the process and 2) it moves any offset/indexing/f(i) style logic out of the loop.
This turns out to actually be pretty easy to implement. SCEV already has all the information we need to know what the backedge taken count is for each individual exit. (We use that when computing the BE taken count for the loop as a whole.) We basically just need to iterate through the exiting blocks and apply the existing logic with the exit specific BE taken count. (The previously landed NFC makes this super obvious.)
I chose to go ahead and apply this to all loop exits instead of only latch exits as originally proposed. After reviewing other passes, the only case I could find where LFTR form was harmful was LoopPredication. I've fixed the latch case, and guards aren't LFTRed anyways. We'll have some more work to do on the way towards widenable_conditions, but that's easily deferred.
I do want to note that I added one bit after the review. When running tests, I saw a new failure (no idea why didn't see previously) which pointed out LFTR can rewrite a constant condition back to a loop varying one. This was theoretically possible with a single exit, but the zero case covered it in practice. With multiple exits, we saw this happening in practice for the eliminate-comparison.ll test case because we'd compute a ExitCount for one of the exits which was guaranteed to never actually be reached. Since LFTR ran after simplifyAndExtend, we'd immediately turn around and undo the simplication work we'd just done. The solution seemed obvious, so I didn't bother with another round of review.
Differential Revision: https://reviews.llvm.org/D62625
llvm-svn: 363883
(Recommit of r363293 which was reverted when a dependent patch was.)
As pointed out by Nikita in D62625, BackedgeTakenCount is generally used to refer to the backedge taken count of the loop. A conditional backedge taken count - one which only applies if a particular exit is taken - is called a ExitCount in SCEV code, so be consistent here.
llvm-svn: 363875
[SROA] Enhance SROA to handle `addrspacecast`ed allocas
- Fix typo in original change
- Add additional handling to ensure all return pointers are properly
casted.
Summary:
- After `addrspacecast` is allowed to be eliminated in SROA, the
adjusting of storage pointer (from `alloca) needs to handle the
potential different address spaces between the storage pointer (from
alloca) and the pointer being used.
Reviewers: arsenm
Subscribers: wdng, hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D63501
llvm-svn: 363743
Summary:
- After `addrspacecast` is allowed to be eliminated in SROA, the
adjusting of storage pointer (from `alloca) needs to handle the
potential different address spaces between the storage pointer (from
alloca) and the pointer being used.
Reviewers: arsenm
Subscribers: wdng, hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D63501
llvm-svn: 363711
This patch really contains two pieces:
Teach SCEV how to fold a phi in the header of a loop to the value on the backedge when a) the backedge is known to execute at least once, and b) the value is safe to use globally within the scope dominated by the original phi.
Teach IndVarSimplify's rewriteLoopExitValues to allow loop invariant expressions which already exist (and thus don't need new computation inserted) even in loops where we can't optimize away other uses.
Differential Revision: https://reviews.llvm.org/D63224
llvm-svn: 363619
Recommit r363289 with a bug fix for crash identified in pr42279. Issue was that a loop exit test does not have to be an icmp, leading to a null dereference crash when new logic was exercised for that case. Test case previously committed in r363601.
Original commit comment follows:
This contains fixes for two cases where we might invalidate inbounds and leave it stale in the IR (a miscompile). Case 1 is when switching to an IV with no dynamically live uses, and case 2 is when doing pre-to-post conversion on the same pointer type IV.
The basic scheme used is to prove that using the given IV (pre or post increment forms) would have to already trigger UB on the path to the test we're modifying. As such, our potential UB triggering use does not change the semantics of the original program.
As was pointed out in the review thread by Nikita, this is defending against a separate issue from the hasConcreteDef case. This is about poison, that's about undef. Unfortunately, the two are different, see Nikita's comment for a fuller explanation, he explains it well.
(Note: I'm going to address Nikita's last style comment in a separate commit just to minimize chance of subtle bugs being introduced due to typos.)
Differential Revision: https://reviews.llvm.org/D62939
llvm-svn: 363613
Summary:
Update compare normalization in SimpleValue hashing to break ties (when
the same value is being compared to itself) by switching to the swapped
predicate if it has a lower numerical value. This brings the hashing in
line with isEqual, which already recognizes the self-compares with
swapped predicates as equal.
Fixes PR 42280.
Reviewers: spatel, efriedma, nikic, fhahn, uabelho
Reviewed By: nikic
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D63349
llvm-svn: 363598
Summary:
There is PHINode::getBasicBlockIndex() and PHINode::setIncomingValue()
but no function to replace incoming value for a specified BasicBlock*
predecessor.
Clearly, there are a lot of places that could use that functionality.
Reviewer: craig.topper, lebedev.ri, Meinersbur, kbarton, fhahn
Reviewed By: Meinersbur, fhahn
Subscribers: fhahn, hiraditya, zzheng, jsji, llvm-commits
Tag: LLVM
Differential Revision: https://reviews.llvm.org/D63338
llvm-svn: 363566
If an addrspacecast needed to be inserted again, this was creating a
clone of the original cast for each user. Just use the original, which
also saves losing the value name.
llvm-svn: 363562
There is a circular dependency between SROA and InferAddressSpaces
today that requires running both multiple times in order to be able to
eliminate all simple allocas and addrspacecasts. InferAddressSpaces
can't remove addrspacecasts when written to memory, and SROA helps
move pointers out of memory.
This should avoid inserting new commuting addrspacecasts with GEPs,
since there are unresolved questions about pointer wrapping between
different address spaces.
For now, don't replace volatile operations that don't match the alloca
addrspace, as it would change the address space of the access. It may
be still OK to insert an addrspacecast from the new alloca, but be
more conservative for now.
llvm-svn: 363462
As pointed out by Nikita in D62625, BackedgeTakenCount is generally used to refer to the backedge taken count of the loop. A conditional backedge taken count - one which only applies if a particular exit is taken - is called a ExitCount in SCEV code, so be consistent here.
llvm-svn: 363293
This contains fixes for two cases where we might invalidate inbounds and leave it stale in the IR (a miscompile). Case 1 is when switching to an IV with no dynamically live uses, and case 2 is when doing pre-to-post conversion on the same pointer type IV.
The basic scheme used is to prove that using the given IV (pre or post increment forms) would have to already trigger UB on the path to the test we're modifying. As such, our potential UB triggering use does not change the semantics of the original program.
As was pointed out in the review thread by Nikita, this is defending against a separate issue from the hasConcreteDef case. This is about poison, that's about undef. Unfortunately, the two are different, see Nikita's comment for a fuller explanation, he explains it well.
(Note: I'm going to address Nikita's last style comment in a separate commit just to minimize chance of subtle bugs being introduced due to typos.)
Differential Revision: https://reviews.llvm.org/D62939
llvm-svn: 363289
Summary:
The logic in EarlyCSE that looks through 'not' operations in the
predicate recognizes e.g. that `select (not (cmp sgt X, Y)), X, Y` is
equivalent to `select (cmp sgt X, Y), Y, X`. Without this change,
however, only the latter is recognized as a form of `smin X, Y`, so the
two expressions receive different hash codes. This leads to missed
optimization opportunities when the quadratic probing for the two hashes
doesn't happen to collide, and assertion failures when probing doesn't
collide on insertion but does collide on a subsequent table grow
operation.
This change inverts the order of some of the pattern matching, checking
first for the optional `not` and then for the min/max/abs patterns, so
that e.g. both expressions above are recognized as a form of `smin X, Y`.
It also adds an assertion to isEqual verifying that it implies equal
hash codes; this fires when there's a collision during insertion, not
just grow, and so will make it easier to notice if these functions fall
out of sync again. A new flag --earlycse-debug-hash is added which can
be used when changing the hash function; it forces hash collisions so
that any pair of values inserted which compare as equal but hash
differently will be caught by the isEqual assertion.
Reviewers: spatel, nikic
Reviewed By: spatel, nikic
Subscribers: lebedev.ri, arsenm, craig.topper, efriedma, hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D62644
llvm-svn: 363274
This case is slightly tricky, because loop distribution should be
allowed in some cases, and not others. As long as runtime dependency
checks don't need to be introduced, this should be OK. This is further
complicated by the fact that LoopDistribute partially ignores if LAA
says that vectorization is safe, and then does its own runtime pointer
legality checks.
Note this pass still does not handle noduplicate correctly, as this
should always be forbidden with it. I'm not going to bother trying to
fix it, as it would require more effort and I think noduplicate should
be removed.
https://reviews.llvm.org/D62607
llvm-svn: 363160
Yevgeny Rouban