Only fetch preheader once we want to actually hoist. It turns out
that calculating the preheader is expensive enough to affect
overall compile-time if you do it for every single instruction.
Addresses the compile-time regression from D143726.
We can handle logical AND/OR in the same way as arithmetic AND/OR, it only
takes us freezing `RHS2` for which we may introduce a new use which didn't
exist before dynamically.
Differential Revision: https://reviews.llvm.org/D145771
Reviewed By: nikic
We don't do this transform in InstCombine in general case for arbitrary values, because cost of
AND and 2 ICMP's isn't higher than of MIN and ICMP. However, LICM also has a notion
about the loop structure. This transform becomes profitable if `A` and `B` are loop-invariant and
`X` is not: by doing this, we can compute min outside the loop.
Differential Revision: https://reviews.llvm.org/D143726
Reviewed By: nikic
Invariant.group's are not sufficiently handled by LICM. Specifically,
if a given invariant.group loaded pointer is not overwritten between
the start of a loop, and its use in the load, it can be hoisted.
The invariant.group (on an already invariant pointer operand) ensures
the result is the same. If it is not overwritten between the start
of the loop and the load, it is therefore legal to hoist.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D144053
During scalar promotion, if there are additional potentially-aliasing
loads outside the promoted set, we can still perform a load-only
promotion. As the stores are retained, any potentially-aliasing
loads will still read the correct value.
This increases the number of load promotions in llvm-test-suite by
a factor of two:
| Old | New
licm.NumPromotionCandidates | 4448 | 6038
licm.NumLoadPromoted | 479 | 1069
licm.NumLoadStorePromoted | 1459 | 1459
Unfortunately, this does have some impact on compile-time:
http://llvm-compile-time-tracker.com/compare.php?from=57f7f0d6cf0706a88e1ecb74f3d3e8891cceabfa&to=72b811738148aab399966a0435f13b695da1c1c8&stat=instructions
In part this is because we now have less early bailouts from
promotion, but also due to second order effects (e.g. for one case
I looked at we spend more time in SLP now).
Differential Revision: https://reviews.llvm.org/D133192
We already collect all instructions that need to be promoted. The
custom isInstInList() implementation could provide incorrect
results if a new use of the original pointer was introduced as
part of promotion. This probably cannot happen with normal code,
because of the pointer capture, but it can happen with a null
pointer.
Fixes https://github.com/llvm/llvm-project/issues/59324.
D138014 restricted AST to work on immutable IR. This means it is
also safe to use a single BatchAA instance for the entire AST
lifetime, instead of only batching parts of individual queries.
The primary motivation for this is not compile-time, but rather
having a central place to control cross-iteration AA, which will
be used by D137958.
Differential Revision: https://reviews.llvm.org/D137955
The Assignment Tracking debug-info feature is outlined in this RFC:
https://discourse.llvm.org/t/
rfc-assignment-tracking-a-better-way-of-specifying-variable-locations-in-ir
Merge DIAssignID attachments on stores that are merged and sunk out of
loops. The store may be sunk into multiple exit blocks, and in this case all
the copies of the store get the same DIAssignID.
Reviewed By: jmorse
Differential Revision: https://reviews.llvm.org/D133313
The pointsToConstantMemory() method returns true only if the memory pointed to
by the memory location is globally invariant. However, the LLVM memory model
also has the semantic notion of *locally-invariant*: memory that is known to be
invariant for the life of the SSA value representing that pointer. The most
common example of this is a pointer argument that is marked readonly noalias,
which the Rust compiler frequently emits.
It'd be desirable for LLVM to treat locally-invariant memory the same way as
globally-invariant memory when it's safe to do so. This patch implements that,
by introducing the concept of a *ModRefInfo mask*. A ModRefInfo mask is a bound
on the Mod/Ref behavior of an instruction that writes to a memory location,
based on the knowledge that the memory is globally-constant memory (in which
case the mask is NoModRef) or locally-constant memory (in which case the mask
is Ref). ModRefInfo values for an instruction can be combined with the
ModRefInfo mask by simply using the & operator. Where appropriate, this patch
has modified uses of pointsToConstantMemory() to instead examine the mask.
The most notable optimization change I noticed with this patch is that now
redundant loads from readonly noalias pointers can be eliminated across calls,
even when the pointer is captured. Internally, before this patch,
AliasAnalysis was assigning Ref to reads from constant memory; now AA can
assign NoModRef, which is a tighter bound.
Differential Revision: https://reviews.llvm.org/D136659
Followup to D135962 to rename remaining uses of
FunctionModRefBehavior to MemoryEffects. Does not touch API names
yet, but also updates variables names FMRB/MRB to ME, to match the
new type name.
If the single-thread model is used, or the
-licm-force-thread-model-single flag is specified, skip checks
related to thread-safety. This means that store promotion for
conditionally executed stores only requires proof of
dereferenceability and writability, but not of thread-safety. For
example, this enables promotion of stores to (non-constant) globals,
as well as captured allocas.
Fixes https://github.com/llvm/llvm-project/issues/50537.
Differential Revision: https://reviews.llvm.org/D130466
Collect more statistics for scalar promotion. In particular,
keep track of how many promotion candidates there were, and
whether it is a load or a load/store promotion.
Currently, FunctionModRefBehavior tracks whether the function reads
or writes memory (ModRefInfo) and which locations it can access
(argmem, inaccessiblemem and other). This patch changes it to track
ModRef information per-location instead.
To give two examples of why this is useful:
* D117095 highlights a weakness of ModRef modelling in the presence
of operand bundles. For a memcpy call with deopt operand bundle,
we want to say that it can read any memory, but only write argument
memory. This would allow them to be treated like any other calls.
However, we currently can't express this and have to say that it
can read or write any memory.
* D127383 would ideally be modelled as a separate threadid location,
where threadid Refs outside pre-split coroutines can be ignored
(like other accesses to constant memory). The current representation
does not allow modelling this precisely.
The patch as implemented is intended to be NFC, but there are some
obvious opportunities for improvements and simplification. To fully
capitalize on this we would also want to change the way we represent
memory attributes on functions, but that's a larger change, and I
think it makes sense to separate out the FunctionModRefBehavior
refactoring.
Differential Revision: https://reviews.llvm.org/D130896
If there are non-load/store users of the promoted pointer, we
currently abort promotion. However, having such users isn't really
relevant to the transform. We already separately check that a)
there are no instructions that modref the promoted pointer and
b) that a pointer capture disables store promotion.
In the affected @test_captured_in_loop test case we have a readnone
capture of the promoted pointer, which means that load promotion
can be performed (while store promotion cannot).
Differential Revision: https://reviews.llvm.org/D133485
This used a single check to make sure that the object is both
writable and thread-local. Separate them out to make the
deficiencies in the current code more obvious.
Currently, we bail out of scalar promotion if the loop may unwind
and the memory may be visible on unwind. This is because we can't
insert stores of the promoted value on unwind edges.
However, nowadays scalar promotion also has support for only
promoting loads, while leaving stores in place. This kind of
promotion is safe even in the presence of unwinding.
Differential Revision: https://reviews.llvm.org/D133111
This code was relying on a very subtle contract: The expectation
was that for non-allocas, the unwind safety check would already
perform a capture check, so we don't need to perform it later.
This held true when this unwind safety was only handled for allocas
and noalias calls, but became incorrect when byval support was
added.
To avoid this kind of issue, just remove the dependency between the
unwind and thread-safety checks entirely. At worst, this means we
perform a redundant capture check. If this should turn out to be
problematic for compile-time, we can cache that query in a more
explicit way.
* Replace getUserCost with getInstructionCost, covering all cost kinds.
* Remove getInstructionLatency, it's not implemented by any backends, and we should fold the functionality into getUserCost (now getInstructionCost) to make it easier for targets to handle the cost kinds with their existing cost callbacks.
Original Patch by @samparker (Sam Parker)
Differential Revision: https://reviews.llvm.org/D79483
SplitBlockPredecessors currently asserts if one of the predecessor
terminators is a callbr. This limitation was originally necessary,
because just like with indirectbr, it was not possible to replace
successors of a callbr. However, this is no longer the case since
D67252. As the requirement nowadays is that callbr must reference
all blockaddrs directly in the call arguments, and these get
automatically updated when setSuccessor() is called, we no longer
need this limitation.
The only thing we need to do here is use replaceSuccessorWith()
instead of replaceUsesOfWith(), because only the former does the
necessary blockaddr updating magic.
I believe there's other similar limitations that can be removed,
e.g. related to critical edge splitting.
Differential Revision: https://reviews.llvm.org/D129205
This reverts the revert commit ad95255b9215a.
The updated version also creates a load when the store may not execute.
In those cases, we still need to introduce a load in a function where
there may not have been one before, so this doesn't completely resolve
issue #51248.
Original message:
When only a store is sunk, there is no need to create a load in the
pre-header, as the result of the load will never get used.
The dead load can can introduce UB, if the function is marked as
writeonly.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D123473
This reverts the revert commit 1ddc719680c21f3.
This version of the patch sets the initial available value to poison,
which resolves an issue with the SSAUpdater breaking LCSSA form.
When only a store is sunk, there is no need to create a load in the
pre-header, as the result of the load will never get used.
The dead load can can introduce UB, if the function is marked as
writeonly.
Fixes#51248.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D123473
This makes MemorySSA in LoopSink required, and removes the AST-based
implementation, as well as the related support code in LICM.
Differential Revision: https://reviews.llvm.org/D123288
