When we check if a load is loop invariant by finding a dominating
invariant.start call, we strip bitcasts until we get to an i8* Value,
and look for an invariant.start use of the i8* Value.
We may accidentally end up at an i8 global and look at a global's uses,
which we shouldn't do in a loop pass. Although we could make this
logic work with globals, that's not currently intended.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D111098
MSSA-based LICM has been enabled by default for a few years now.
This drops the old AST-based implementation. Using loop(licm) will
result in a fatal error, the use of loop-mssa(licm) is required
(or just licm, which defaults to loop-mssa).
Note that the core canSinkOrHoistInst() logic has to retain AST
support for now, because it is shared with LoopSink.
Differential Revision: https://reviews.llvm.org/D108244
This was a diagnostic option used to demonstrate a weakness in
the AST-based LICM implementation. This problem does not exist
in the MSSA-based LICM implementation, which has been enabled
for a long time now. As such, this option is no longer relevant.
This option has been enabled by default for quite a while now.
The practical impact of removing the option is that MSSA use
cannot be disabled in default pipelines (both LPM and NPM) and
in manual LPM invocations. NPM can still choose to enable/disable
MSSA using loop vs loop-mssa.
The next step will be to require MSSA for LICM and drop the
AST-based implementation entirely.
Differential Revision: https://reviews.llvm.org/D108075
This is enabled by default. Drop explicit uses in preparation for
removing the option.
Also drop RUN lines that are now the same (typically modulo a
-verify-memoryssa option).
Currently, LNICM pass does not support sinking instructions out of loop nest.
This patch enables LNICM to sink down as many instructions to the exit block of outermost loop as possible.
Reviewed By: Whitney
Differential Revision: https://reviews.llvm.org/D107219
When hoisting/moving calls to locations, we strip unknown metadata. Such calls are usually marked `speculatable`, i.e. they are guaranteed to not cause undefined behaviour when run anywhere. So, we should strip attributes that can cause immediate undefined behaviour if those attributes are not valid in the context where the call is moved to.
This patch introduces such an API and uses it in relevant passes. See
updated tests.
Fix for PR50744.
Reviewed By: nikic, jdoerfert, lebedev.ri
Differential Revision: https://reviews.llvm.org/D104641
Proposed alternative to D105338.
This is ugly, but short-term I think it's the best way forward: first,
let's formalize the hacks into a coherent model. Then we can consider
extensions of that model (we could have different flavors of volatile
with different rules).
Differential Revision: https://reviews.llvm.org/D106309
This adjusts mayHaveSideEffect() to return true for !willReturn()
instructions. Just like other side-effects, non-willreturn calls
(aka "divergence") cannot be removed and cannot be reordered relative
to other side effects. This fixes a number of bugs where
non-willreturn calls are either incorrectly dropped or moved. In
particular, it also fixes the last open problem in
https://bugs.llvm.org/show_bug.cgi?id=50511.
I performed a cursory review of all current mayHaveSideEffect()
uses, which convinced me that these are indeed the desired default
semantics. Places that do not want to consider non-willreturn as a
sideeffect generally do not want mayHaveSideEffect() semantics at
all. I identified two such cases, which are addressed by D106591
and D106742. Finally, there is a use in SCEV for which we don't
really have an appropriate API right now -- what it wants is
basically "would this be considered forward progress". I've just
spelled out the previous semantics there.
Differential Revision: https://reviews.llvm.org/D106749
This patch adds a new pass called LNICM which is a LoopNest version of LICM and a test case to show how LNICM works.
Basically, LNICM only hoists invariants out of loop nest (not a loop) to keep/make perfect loop nest. This enables later optimizations that require perfect loop nest.
Reviewed By: Whitney
Differential Revision: https://reviews.llvm.org/D104180
There's a potential change in dereferenceability attribute semantics in the nearish future. See llvm-dev thread "RFC: Decomposing deref(N) into deref(N) + nofree" and D99100 for context.
This change simply adds appropriate attributes to tests to keep transform logic exercised under both old and new/proposed semantics. Note that for many of these cases, O3 would infer exactly these attributes on the test IR.
This change handles the idiomatic pattern of a dereferenceable object being passed to a call which can not free that memory. There's a couple other tests which need more one-off attention, they'll be handled in another change.
Reapply with fixes for clang tests.
-----
This is a simple enum attribute. Test changes are because enum
attributes are sorted before type attributes, so mustprogress is
now in a different position.
This can be seen as a follow up to commit 0ee439b705,
that changed the second argument of __powidf2, __powisf2 and
__powitf2 in compiler-rt from si_int to int. That was to align with
how those runtimes are defined in libgcc.
One thing that seem to have been missing in that patch was to make
sure that the rest of LLVM also handle that the argument now depends
on the size of int (not using the si_int machine mode for 32-bit).
When using __builtin_powi for a target with 16-bit int clang crashed.
And when emitting libcalls to those rtlib functions, typically when
lowering @llvm.powi), the backend would always prepare the exponent
argument as an i32 which caused miscompiles when the rtlib was
compiled with 16-bit int.
The solution used here is to use an overloaded type for the second
argument in @llvm.powi. This way clang can use the "correct" type
when lowering __builtin_powi, and then later when emitting the libcall
it is assumed that the type used in @llvm.powi matches the rtlib
function.
One thing that needed some extra attention was that when vectorizing
calls several passes did not support that several arguments could
be overloaded in the intrinsics. This patch allows overload of a
scalar operand by adding hasVectorInstrinsicOverloadedScalarOpd, with
an entry for powi.
Differential Revision: https://reviews.llvm.org/D99439
The MaybePromotable set keeps track of loads/stores for which
promotion was not attempted yet. Normally, any load/stores that
are promoted in the current iteration will be removed from this
set, because they naturally MustAlias with the promoted value.
However, if the source program has UB with metadata claiming that
a store is NoAlias, while it is actually MustAlias, and multiple
different pointers are promoted in the same iteration, it can
happen that a store is removed that is still in the MaybePromotable
set, causing a use-after-free.
While this could be fixed by explicitly invalidating values in
MaybePromotable in the LoopPromoter, I'm going with the more
radical option of dropping the set entirely here and check all
load/stores on each promotion iteration. As promotion, and especially
repeated promotion, are quite rare, this doesn't seem to have any
impact on compile-time.
Fixes https://bugs.llvm.org/show_bug.cgi?id=50367.
This appears to miscompile google benchmark's GetCacheSizesFromKVFS()
when compiling with -fstrict-vtable-pointers.
Runnable reproducer: https://godbolt.org/z/f9ovKqTzb
The "f.fail()" crashes with BUS error, it is compiled into testb,
and the adress it is testing is non-sensical.
This reverts commit 4c89bcadf6.
During store promotion, we check whether the pointer was captured
to exclude potential reads from other threads. However, we're only
interested in captures before or inside the loop. Check this using
PointerMayBeCapturedBefore against the loop header.
Differential Revision: https://reviews.llvm.org/D100706
This patch clarifies the semantics of the nofree function attribute to make clear that it provides an "as if" semantic. That is, a nofree function is guaranteed not to free memory which existed before the call, but might allocate and then deallocate that same memory within the lifetime of the callee.
This is the result of the discussion on llvm-dev under the thread "Ambiguity in the nofree function attribute".
The most important part of this change is the LangRef wording. The rest is minor comment changes to emphasize the new semantics where code was accidentally consistent, and fix one place which wasn't consistent. That one place is currently narrowly used as it is primarily part of the ongoing (and not yet enabled) deref-at-point semantics work.
Differential Revision: https://reviews.llvm.org/D100141
This reverts commit ab98f2c712 and 98eea392cd.
It includes a fix for the clang test which triggered the revert. I failed to notice this one because there was another AMDGPU llvm test with a similiar name and the exact same text in the error message. Odd. Since only one build bot reported the clang test, I didn't notice that one.
Breaks check-clang, see comments on D100400
Also revert follow-up "[NFC] Move a recently added utility into a location to enable reuse"
This reverts commit 3ce61fb6d6.
This reverts commit 61a85da882.
We have some cases today where attributes can be inferred from another on access, but the result is not explicitly materialized in IR. This change is a step towards changing that.
Why? Two main reasons:
* Human clarity. It's really confusing trying to figure out why a transform is triggering when the IR doesn't appear to have the required attributes.
* This avoids the need to special case declarations in e.g. functionattrs. Since we can assume the attribute is present, we can work directly from attributes (and only attributes) without also needing to query accessors on Function to avoid missing cases due to unannotated (but infered on use) declarations. (This piece will appear must easier to follow once D100226 also lands.)
Differential Revision: https://reviews.llvm.org/D100400
Previously loading the vtable used in calling a virtual method in a loop
was not hoisted out of the loop. This fixes that.
canSinkOrHoistInst() itself doesn't check that the load operands are
loop invariant, callers also check that separately.
Reviewed By: rnk
Differential Revision: https://reviews.llvm.org/D99784
Hookup TLI when inferring object size from allocation calls. This allows the analysis to prove dereferenceability for known allocation functions (such as malloc/new/etc) in addition to those marked explicitly with the allocsize attribute.
This is a follow up to 0129cd5 now that the bug fixed by e2c6621e6 is resolved.
As noted in the test, this relies on being able to prove that there is no free between allocation and context (e.g. hoist location). At the moment, this is handled conservatively. I'm working strengthening out ability to reason about no-free regions separately.
Differential Revision: https://reviews.llvm.org/D99737
Support deriving dereferenceability facts from allocation sites with known object sizes while correctly accounting for any possibly frees between allocation and use site. (At the moment, we're conservative and only allowing it in functions where we know we can't free.)
This is part of the work on deref-at-point semantics. I'm making the change unconditional as the miscompile in this case is way too easy to trip by accident, and the optimization was only recently added (by me).
There will be a follow up patch wiring through TLI since that should now be doable without introducing widespread miscompiles.
Differential Revision: https://reviews.llvm.org/D95815
MCJIT served well as the default JIT engine in lli for a long time, but the code is getting old and maintenance efforts don't seem to be in sight. In the meantime Orc became mature enough to fill that gap. The newly added greddy mode is very similar to the execution model of MCJIT. It should work as a drop-in replacement for common JIT tasks.
Reviewed By: lhames
Differential Revision: https://reviews.llvm.org/D98931
MCJIT served well as the default JIT engine in lli for a long time, but the code is getting old and maintenance efforts don't seem to be in sight. In the meantime Orc became mature enough to fill that gap. The newly added greddy mode is very similar to the execution model of MCJIT. It should work as a drop-in replacement for common JIT tasks.
Reviewed By: lhames
Differential Revision: https://reviews.llvm.org/D98931
It is not legal to form a phi node with token type. The generic LCSSA construction code handles this correctly - by not forming LCSSA for such cases - but the adhoc fixup implementation in LICM did not.
This was noticed in the context of PR49607, but can be demonstrated on ToT with the tweaked test case. This is not specific to gc.relocate btw, it also applies to usage of the preallocated family of intrinsics as well.
Differential Revision: https://reviews.llvm.org/D98728
As readnone function they become movable and LICM can hoist them
out of a loop. As a result in LCSSA form phi node of type token
is created. No one is ready that GCRelocate first operand is phi node
but expects to be token.
GVN test were also updated, it seems it does not do what is expected.
Test for LICM is also added.
This reverts commit f352463ade.
Relative to the previous implementation, this always uses
aliasesUnknownInst() instead of aliasesPointer() to correctly
handle atomics. The added test case was previously miscompiled.
-----
Even when MemorySSA-based LICM is used, an AST is still populated
for scalar promotion. As the AST has quadratic complexity, a lot
of time is spent in this step despite the existing access count
limit. This patch optimizes the identification of promotable stores.
The idea here is pretty simple: We're only interested in must-alias
mod sets of loop invariant pointers. As such, only populate the AST
with loop-invariant loads and stores (anything else is definitely
not promotable) and then discard any sets which alias with any of
the remaining, definitely non-promotable accesses.
If we promoted something, check whether this has made some other
accesses loop invariant and thus possible promotion candidates.
This is much faster in practice, because we need to perform AA
queries for O(NumPromotable^2 + NumPromotable*NumNonPromotable)
instead of O(NumTotal^2), and NumPromotable tends to be small.
Additionally, promotable accesses have loop invariant pointers,
for which AA is cheaper.
This has a signicant positive compile-time impact. We save ~1.8%
geomean on CTMark at O3, with 6% on lencod in particular and 25%
on individual files.
Conceptually, this change is NFC, but may not be so in practice,
because the AST is only an approximation, and can produce
different results depending on the order in which accesses are
added. However, there is at least no impact on the number of promotions
(licm.NumPromoted) in test-suite O3 configuration with this change.
Differential Revision: https://reviews.llvm.org/D89264
See pr46990(https://bugs.llvm.org/show_bug.cgi?id=46990). LICM should not sink store instructions to loop exit blocks which cross coro.suspend intrinsics. This breaks semantic of coro.suspend intrinsic which return to caller directly. Also this leads to use-after-free if the coroutine is freed before control returns to the caller in multithread environment.
This patch disable promotion by check whether loop contains coro.suspend intrinsics.
This is a resubmit of D86190.
Disabling LICM for loops with coroutine suspension is a better option not only for correctness purpose but also for performance purpose.
In most cases LICM sinks memory operations. In the case of coroutine, sinking memory operation out of the loop does not improve performance since coroutien needs to get data from the frame anyway. In fact LICM would hurt coroutine performance since it adds more entries to the frame.
Differential Revision: https://reviews.llvm.org/D96928
The main point of committing this early is to have a negative test in tree. Nothing fails in the current tests if we implement this (currently unsound) optimization.
This patch marks some library functions as willreturn. On the first pass, I
excluded most functions that interact with streams/the filesystem.
Along with willreturn, it also adds nounwind to a set of math functions.
There probably are a few additional attributes we can add for those, but
that should be done separately.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D94684
