This cleans up all LoadInst creation in LLVM to explicitly pass the
value type rather than deriving it from the pointer's element-type.
Differential Revision: https://reviews.llvm.org/D57172
llvm-svn: 352911
Summary:
MemorySSA needs updating each time an instruction is moved.
LICM and control flow hoisting re-hoists instructions, thus needing another update when re-moving those instructions.
Pending cleanup: the MSSA update is duplicated, should be moved inside moveInstructionBefore.
Reviewers: jnspaulsson
Subscribers: sanjoy, jlebar, Prazek, george.burgess.iv, llvm-commits
Differential Revision: https://reviews.llvm.org/D57176
llvm-svn: 352092
to reflect the new license.
We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.
Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.
llvm-svn: 351636
Summary:
Step 2 in using MemorySSA in LICM:
Use MemorySSA in LICM to do sinking and hoisting, all under "EnableMSSALoopDependency" flag.
Promotion is disabled.
Enable flag in LICM sink/hoist tests to test correctness of this change. Moved one test which
relied on promotion, in order to test all sinking tests.
Reviewers: sanjoy, davide, gberry, george.burgess.iv
Subscribers: llvm-commits, Prazek
Differential Revision: https://reviews.llvm.org/D40375
llvm-svn: 350879
Current strategy of dropping `InstructionPrecedenceTracking` cache is to
invalidate the entire basic block whenever we change its contents. In fact,
`InstructionPrecedenceTracking` has 2 internal strictures: `OrderedInstructions`
that is needed to be invalidated whenever the contents changes, and the map
with first special instructions in block. This second map does not need an
update if we add/remove a non-special instuction because it cannot
affect the contents of this map.
This patch changes API of `InstructionPrecedenceTracking` so that it now
accounts for reasons under which we invalidate blocks. This should lead
to much less recalculations of the map and should save us some compile time
because in practice we don't typically add/remove special instructions.
Differential Revision: https://reviews.llvm.org/D54462
Reviewed By: efriedma
llvm-svn: 350694
In some cases the order that we hoist instructions in means that when rehoisting
(which uses the same order as hoisting) we can rehoist to a block A, then a
block B, then block A again. This currently causes an assertion failure as it
expects that when changing the hoist point it only ever moves to a block that
dominates the hoist point being moved from.
Fix this by moving the re-hoist point when it doesn't dominate the dominator of
hoisted instruction, or in other words when it wouldn't dominate the uses of
the instruction being rehoisted.
Differential Revision: https://reviews.llvm.org/D55266
llvm-svn: 350408
Summary:
The remaining code paths that ControlFlowHoisting introduced that were
not disabled, increased compile time by 3x for some benchmarks.
The time is spent in DominatorTree updates.
Reviewers: john.brawn, mkazantsev
Subscribers: sanjoy, jlebar, llvm-commits
Differential Revision: https://reviews.llvm.org/D55313
llvm-svn: 348345
This commit caused a large compile-time slowdown in some cases when NDEBUG is
off due to the dominator tree verification it added. Fix this by only doing
dominator tree and loop info verification when something has been hoisted.
Differential Revision: https://reviews.llvm.org/D52827
llvm-svn: 347889
This reverts commits r347776 and r347778.
The first one, r347776, caused significant compile time regressions
for certain input files, see PR39836 for details.
llvm-svn: 347867
This commit caused failures because it failed to correctly handle cases where
we hoist a phi, then hoist a use of that phi, then have to rehoist that use. We
need to make sure that we rehoist the use to _after_ the hoisted phi, which we
do by always rehoisting to the immediate dominator instead of just rehoisting
everything to the original preheader.
An option is also added to control whether control flow is hoisted, which is
off in this commit but will be turned on in a subsequent commit.
Differential Revision: https://reviews.llvm.org/D52827
llvm-svn: 347776
The general approach taken is to make note of loop invariant branches, then when
we see something conditional on that branch, such as a phi, we create a copy of
the branch and (empty versions of) its successors and hoist using that.
This has no impact by itself that I've been able to see, as LICM typically
doesn't see such phis as they will have been converted into selects by the time
LICM is run, but once we start doing phi-to-select conversion later it will be
important.
Differential Revision: https://reviews.llvm.org/D52827
llvm-svn: 347190
This patch relaxes overconservative checks on whether or not we could write
memory before we execute an instruction. This allows us to hoist guards out of
loops even if they are not in the header block.
Differential Revision: https://reviews.llvm.org/D50891
Reviewed By: fedor.sergeev
llvm-svn: 346643
LICM relies on variable `MustExecute` which is conservatively set to `false`
in all non-headers. It is used when we decide whether or not we want to hoist
an instruction or a guard.
For the guards, it might be too conservative to use this variable, we can
instead use a more precise logic from LoopSafetyInfo. Currently it is only NFC
because `IsMemoryNotModified` is also conservatively set to `false` for all
non-headers, and we cannot hoist guards from non-header blocks. However once we
give up using `IsMemoryNotModified` and use a smarter check instead, this will
allow us to hoist guards from all mustexecute non-header blocks.
Differential Revision: https://reviews.llvm.org/D50888
Reveiwed By: fedor.sergeev
llvm-svn: 346204
This patch makes LICM use `ICFLoopSafetyInfo` that is a smarter version
of LoopSafetyInfo that leverages power of Implicit Control Flow Tracking
to keep track of throwing instructions and give less pessimistic answers
to queries related to throws.
The ICFLoopSafetyInfo itself has been introduced in rL344601. This patch
enables it in LICM only.
Differential Revision: https://reviews.llvm.org/D50377
Reviewed By: apilipenko
llvm-svn: 346201
This patch factors out a function that makes all required updates
whenever an instruction gets erased.
Differential Revision: https://reviews.llvm.org/D54011
Reviewed By: apilipenko
llvm-svn: 345914
Moving away from UnknownSize is part of the effort to migrate us to
LocationSizes (e.g. the cleanup promised in D44748).
This doesn't entirely remove all of the uses of UnknownSize; some uses
require tweaks to assume that UnknownSize isn't just some kind of int.
This patch is intended to just be a trivial replacement for all places
where LocationSize::unknown() will Just Work.
llvm-svn: 344186
Currently we re-use cached info from sub loops or traverse them
to populate AliasSetTracker. But after that we traverse all basic blocks
from the current loop. This is redundant work.
All what we need is traversing the all basic blocks from the loop except
those which are used to get the data from the cache.
This should improve compile time only.
Reviewers: mkazantsev, reames, kariddi, anna
Reviewed By: reames
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D51715
llvm-svn: 341896
I'd made exactly this same change before, but it appears to have been accidentally reverted in another change. (I'm assuming accidental since it was without comment or test case, and in an unrelated change.)
llvm-svn: 341892
rL340921 has been reverted by rL340923 due to linkage dependency
from Transform/Utils to Analysis which is not allowed. In this patch
this has been fixed, a new utility function moved to Analysis.
Differential Revision: https://reviews.llvm.org/D51152
llvm-svn: 341014
Teach LICM to hoist stores out of loops when the store writes to a location otherwise unused in the loop, writes a value which is invariant, and is guaranteed to execute if the loop is entered.
Worth noting is that this transformation is partially overlapping with the existing promotion transformation. Reasons this is worthwhile anyway include:
* For multi-exit loops, this doesn't require duplication of the store.
* It kicks in for case where we can't prove we exit through a normal exit (i.e. we may throw), but can prove the store executes before that possible side exit.
Differential Revision: https://reviews.llvm.org/D50925
llvm-svn: 340974
We have multiple places in code where we try to identify whether or not
some instruction is a guard. This patch factors out this logic into a separate
utility function which works uniformly in all places.
Differential Revision: https://reviews.llvm.org/D51152
Reviewed By: fedor.sergeev
llvm-svn: 340921
Once the invariant_start is reached, we know that no instruction *after* it can modify the memory. So, if we can prove the location isn't read *between entry into the loop and the execution of the invariant_start*, we can execute the invariant_start before entering the loop.
Differential Revision: https://reviews.llvm.org/D51181
llvm-svn: 340617
Volatility is not an aliasing property. We used to model volatile as if it had extremely conservative aliasing implications, but that hasn't been true for several years now. So, it doesn't make sense to be in AliasSet.
It also turns out the code is entirely a noop. Outside of the AST code to update it, there was only one user: load store promotion in LICM. L/S promotion doesn't need the check since it walks all the users of the address anyway. It already checks each load or store via !isUnordered which causes us to bail for volatile accesses. (Look at the lines immediately following the two remove asserts.)
There is the possibility of some small compile time impact here, but the only case which will get noticeably slower is a loop with a large number of loads and stores to the same address where only the last one we inspect is volatile. This is sufficiently rare it's not worth optimizing for..
llvm-svn: 340312
This patch teaches LICM to hoist guards from the loop if they are guaranteed to execute and
if there are no side effects that could prevent that.
Differential Revision: https://reviews.llvm.org/D50501
Reviewed By: reames
llvm-svn: 340256
Summary:
Currently, in LICM, we use the alias set tracker to identify if the
instruction (we're interested in hoisting) aliases with instruction that
modifies that memory location.
This patch adds an LICM alias analysis diagnostic tool that checks the
mod ref info of the instruction we are interested in hoisting/sinking,
with every instruction in the loop. Because of O(N^2) complexity this
is now only a diagnostic tool to show the limitation we have with the
alias set tracker and is OFF by default.
Test cases show the difference with the diagnostic analysis tool, where
we're able to hoist out loads and readonly + argmemonly calls from the
loop, where the alias set tracker analysis is not able to hoist these
instructions out.
Reviewers: reames, mkazantsev, fedor.sergeev, hfinkel
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D50854
llvm-svn: 340026
Main value is just simplifying code. I'll further simply the argument handling case in a bit, but that involved a slightly orthogonal change so I went with the mildy ugly intermediate for this patch.
Note that the isSized check in the old LICM code was not carried across. It turns out that check was dead. a) no test exercised it, and b) langref and verifier had been updated to disallow unsized types used in loads.
llvm-svn: 339930
If we have an assume which is known to execute and whose operand is invariant, we can lift that into the pre-header. So long as we don't change which paths the assume executes on, this is a legal transformation. It's likely to be a useful canonicalization as other transforms only look for dominating assumes.
Differential Revision: https://reviews.llvm.org/D50364
llvm-svn: 339481
The motivating case is an otherwise dead loop with a fence in it. At the moment, this goes all the way through the optimizer and we end up emitting an entirely pointless loop on x86. This case may seem a bit contrived, but we've seen it in real code as the result of otherwise reasonable lowering strategies combined w/thread local memory optimizations (such as escape analysis).
To handle this simple case, we can teach LICM to hoist must execute fences when there is no other memory operation within the loop.
Differential Revision: https://reviews.llvm.org/D50489
llvm-svn: 339378
This one requires a bit of explaination. It's not every day you simply delete code to implement an optimization. :)
The transform in question is sinking an instruction from a loop to the uses in loop exiting blocks. We know (from LCSSA) that all of the uses outside the loop must be phi nodes, and after predecessor splitting, we know all phi users must have a single operand. Since the use must be strictly dominated by the def, we know from the definition of dominance/ssa that the exit block must execute along a (non-strict) subset of paths which reach the def. As a result, duplicating a potentially faulting instruction can not *introduce* a fault that didn't previously exist in the program.
The full story is that this patch builds on "rL338671: [LICM] Factor out fault legality from canHoistOrSinkInst [NFC]" which pulled this logic out of a common helper routine. As best I can tell, this check was originally added to the helper function for hoisting legality, later an incorrect fastpath for loads/calls was added, and then the bug was fixed by duplicating the fault safety check in the hoist path. This left the redundant check in the common code to pessimize sinking for no reason. I split it out in an NFC, and am not removing the unneccessary check. I wanted there to be something easy to revert in case I missed something.
Reviewed by: Anna Thomas (in person)
llvm-svn: 338794
This method has three callers, each of which wanted distinct handling:
1) Sinking into a loop is moving an instruction known to execute before a loop into the loop. We don't need to worry about introducing a fault at all in this case.
2) Hoisting from a loop into a preheader already duplicated the check in the caller.
3) Sinking from the loop into an exit block was the only true user of the code within the routine. For the moment, this has just been lifted into the caller, but up next is examining the logic more carefully. Whitelisting of loads and calls - while consistent with the previous code - is rather suspicious. Either way, a behavior change is worthy of it's own patch.
llvm-svn: 338671
James Y Knight