In SimplifyCFG we may simplify the CFG by speculatively executing
certain stores, when they are preceded by a store to the same
location. This patch allows such speculation also when the stores are
similarly preceded by a load.
In order for this transformation to be correct we need to ensure that
the memory location is writable and the store in the new location does
not introduce a data race.
Local objects (created by an `alloca` instruction) are always
writable, so once we are past a read from a location it is valid to
also write to that same location.
Seeing just a load does not guarantee absence of a data race (unlike
if we see a store) - the load may still be part of a race, just not
causing undefined behaviour
(cf. https://llvm.org/docs/Atomics.html#optimization-outside-atomic).
In the original program, a data race might have been prevented by the
condition, but once we move the store outside the condition, we must
be sure a data race wasn't possible anyway, no matter what the
condition evaluates to.
One way to be sure that a local object is never concurrently
read/written is check that its address never escapes the function.
Hence this transformation is restricted to local, non-escaping
objects.
Reviewed By: nikic, lebedev.ri
Differential Revision: https://reviews.llvm.org/D107281
This transform has been restricted to legal types since
https://reviews.llvm.org/rG65df808f6254617b9eee931d00e95d900610b660
in 2012.
This is particularly restrictive on RISCV64 which only has i64
as a legal integer type. i32 is a very common type in code
generated from C, but we won't form a lookup table with it.
This also effects other common types like i8/i16 types on ARM,
AArch64, RISCV, etc.
This patch proposes to allow power of 2 types larger than 8 bit, if
they will fit in the largest legal integer type in DataLayout.
These types are common in C code so generally well handled in
the backends.
We could probably do this for other types like i24 and rely on
alignment and padding to allow the backend to use a single wider
load. This isn't my main concern right now and it will need more
tests.
We could also allow larger types up to some limit and let the
backend split into multiple loads, but we need to define that
limit. It's also not my main concern right now.
Reviewed By: lebedev.ri
Differential Revision: https://reviews.llvm.org/D107233
This aligns the multiple exit costing with all the other cost decisions. Note that UnrollAndJam, which is the only other caller of the original home of this code, unconditionally bails out of multiple exit loops.
The option to not preserve LCSSA is in fact not tested at all in upstream. I was tempted to just remove the code entirely, but realized I didn't need to for my actual goal.
I'm working on extending the OptimizeGlobalAddressOfMalloc to handle some more general cases. This is to add support of the ConstantExpr use of the global variables. The function allUsesOfLoadedValueWillTrapIfNull is now iterative with the added CE use of GV. Also, the recursive function valueIsOnlyUsedLocallyOrStoredToOneGlobal is changed to iterative using a worklist with the GEP case added.
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D106589
Reapply commit d675b594f4f1e1f6a195fb9a4fd02cf3de92292d that was
reverted due to buildbot failures. A simple fix has been applied to
remove an assertion.
Differential Revision: https://reviews.llvm.org/D105207
This is a second attempt to fix the EXPENSIVE_CHECKS issue that was mentioned In D91661#2875179 by @jroelofs.
(The first attempt was in D105983)
D91661 more or less completely reverted D49126 and by doing so also removed the cleanup logic of the created declarations and calls.
This patch is a replacement for D91661 (which must itself be reverted first). It replaces the custom declaration creation with the
generic version and shows the test impact. It also tracks the number of NamedValues to detect if a new prototype was added instead
of looking at the available users of a prototype.
Reviewed By: jroelofs
Differential Revision: https://reviews.llvm.org/D106147
This reverts commit 77080a1eb6061df2dcfae8ac84b85ad4d1e02031.
This change introduced issues detected with EXPENSIVE_CHECKS. Reverting to restore the
needed function cleanup. A next patch will then just improve on the name mangling.
Reapply commit 796b84d26f4d461fb50e7b4e84e15a10eaca88fc that was
reverted due to reports of crashes. A minor change now guards against
getVariableLocationOperand() returning a nullptr.
Differential Revision: https://reviews.llvm.org/D106659
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
This reapplies commit 76f3ffb2b285998f02639db8fd42fb0de8a540d0 that was
reverted due to buildbot failures.
- Update lit tests with REQUIRES condition.
- Abandon salvage attempt if SCEVUnknown::getValue() returns nullptr.
Differential Revision: https://reviews.llvm.org/D105207
This patch extends salvaging of debuginfo in the Loop Strength Reduction
(LSR) pass by translating Scalar Evaluations (SCEV) into DIExpressions.
The method is as follows:
- Cache dbg.value intrinsics that are salvageable.
- Obtain a loop Induction Variable (IV) from ScalarExpressionExpander or
the loop header.
- Translate the IV SCEV into an expression that recovers the current
loop iteration count. Combine this with the dbg.value's location
op SCEV to create a DIExpression that salvages the value.
Review by: jmorse
Differential Revision: https://reviews.llvm.org/D105207
Nowadays, simplifycfg pass already tail-merges all the ret blocks together
before doing anything, and it should not increase the count of ret's,
so this is dead code.
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 patch removes RtCheck from RuntimeCheckingPtrGroup to make it
possible to construct RuntimeCheckingPtrGroup objects without a
RuntimePointerChecking object. This should make it easier to
re-use the code to generate runtime checks, e.g. in D102834.
RtCheck was only used to access the pointer info for a given index.
Instead, the start and end expressions can be passed directly.
For code-gen, we also need to know the address space to use. This can
also be explicitly passed at construction.
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D105481
We could try harder to screen out libcalls by
function signature (and that would be a much larger
change than for sprintf alone), but that might make
the transition to type-less pointers more difficult.
https://llvm.org/PR51200
isSafeToSpeculateStore() looks for a preceding store to the same
location to make sure that introducing a new store of the same
value is safe. It currently bails on intervening mayHaveSideEffect()
instructions. However, I believe just checking mayWriteToMemory()
is sufficient there -- we just need to make sure that we know which
value was stored, we don't care if we can unwind in the meantime.
While looking into this, I started having some doubts about the
correctness of the transform with regard to thread safety. While
we don't try to hoist non-simple stores, I believe we also need
to make sure that the preceding store is simple as well. Otherwise
we could introduce a spurious non-atomic write after an atomic write
-- under our memory model this would result in a subsequent undef
atomic read, even if the second write stores the same value as the
first.
Example: https://alive2.llvm.org/ce/z/q_3YAL
Differential Revision: https://reviews.llvm.org/D106742
If the branch isn't `unpredictable`, and it is predicted to *not* branch
to the block we are considering speculatively executing,
then it seems counter-productive to execute the code that is predicted not to be executed.
Reviewed By: spatel
Differential Revision: https://reviews.llvm.org/D106650
Otherwise e.g. the FoldTwoEntryPHINode() has to do a lot of legwork
to re-deduce what is the dominant block (i.e. for which block
is this branch the terminator).
Constfold constrained variants of operations fadd, fsub, fmul, fdiv,
frem, fma and fmuladd.
The change also sets up some means to support for removal of unused
constrained intrinsics. They are declared as accessing memory to model
interaction with floating point environment, so they were not removed,
as they have side effect. Now constrained intrinsics that have
"fpexcept.ignore" as exception behavior are removed if they have no uses.
As for intrinsics that have exception behavior other than "fpexcept.ignore",
they can be removed if it is known that they do not raise floating point
exceptions. It happens when doing constant folding, attributes of such
intrinsic are changed so that the intrinsic is not claimed as accessing
memory.
Differential Revision: https://reviews.llvm.org/D102673
This function is called when some predecessor of an empty return block
ends with a conditional branch, with both successors being empty ret blocks.
Now, because of the way SimplifyCFG works, it might happen to simplify
one of the blocks in a way that makes a conditional branch
into an unconditional one, since it's destinations are now identical,
but it might not have actually simplified said conditional branch
into an unconditional one yet.
So, we have to check that ourselves first,
especially now that SimplifyCFG aggressively tail-merges
all ret and resume blocks.
Even if it was an unconditional branch already,
`SimplifyCFGOpt::simplifyReturn()` doesn't call `FoldReturnIntoUncondBranch()`
by default.
The logical (select) form of and/or will now be a source of problems.
We don't really account for it's inverted form, yet it exists,
and presumably we should treat it just like non-inverted form:
https://alive2.llvm.org/ce/z/BU9AXkhttps://bugs.llvm.org/show_bug.cgi?id=51149 reports a reportedly-serious
perf regression that will hopefully be mitigated by this.
This removes an abuse of ELF linker behaviors while keeping Mach-O/COFF linker
behaviors unchanged.
ELF: when module_ctor is in a comdat, this patch removes reliance on a linker
abuse (an SHT_INIT_ARRAY in a section group retains the whole group) by using
SHF_GNU_RETAIN. No linker behavior difference when module_ctor is not in a comdat.
Mach-O: module_ctor gets `N_NO_DEAD_STRIP`. No linker behavior difference
because module_ctor is already referenced by a `S_MOD_INIT_FUNC_POINTERS`
section (GC root).
PE/COFF: no-op. SanitizerCoverage already appends module_ctor to `llvm.used`.
Other sanitizers: llvm.used for local linkage is not implemented in
`TargetLoweringObjectFileCOFF::emitLinkerDirectives` (once implemented or
switched to a non-local linkage, COFF can use module_ctor in comdat (i.e.
generalize ELF-specific rL301586)).
There is no object file size difference.
Reviewed By: vitalybuka
Differential Revision: https://reviews.llvm.org/D106246
We need to make sure that the value types are the same. Otherwise
we both may not have the necessary dereferenceability implication,
nor can we directly form the desired select pattern.
Without opaque pointers this is enforced implicitly through the
pointer comparison.
When adding noalias/alias.scope metadata, we analyze the instructions
of the original callee, and then place metadata on the corresponding
inlined instructions in the caller as provided by VMap. However, this
assumes that this actually a clone of the instruction, rather than
the result of simplification. If simplification occurred, the
instruction that VMap points to may not have any relationship as far
as ModRef behavior is concerned.
Fix this by tracking simplified instructions during cloning and then
only processing instructions that have not been simplified. This is
done with an additional map form original to cloned instruction,
into which we only insert if no simplification is performed. The
mapping in VMap can then be compared to this map. If they're the
same, the instruction hasn't been simplified. (I originally wanted
to only track a set of simplified instructions, but that wouldn't
work if the instruction only gets simplified afterwards, e.g. based
on rewritten phis.)
Fixes https://bugs.llvm.org/show_bug.cgi?id=50589.
Differential Revision: https://reviews.llvm.org/D106242
This fixes the lower and upper bound calculation of a
RuntimeCheckingPtrGroup when it has more than one loop
invariant pointers. Resolves PR50686.
Reviewed By: fhahn
Differential Revision: https://reviews.llvm.org/D104148
This implements the elementtype attribute specified in D105407. It
just adds the attribute and the specified verifier rules, but
doesn't yet make use of it anywhere.
Differential Revision: https://reviews.llvm.org/D106008
`SinkCommonCodeFromPredecessors()` doesn't itself ensure that duplicate PHI nodes aren't created.
I suppose, we could teach it to do that on-the-fly (& account for the already-existing PHI nodes,
& adjust costmodel), the diff will be bigger than this.
The alternative is to schedule a new EarlyCSE pass invocation somewhere later in the pipeline.
Clearly, we don't have any EarlyCSE runs in module optimization passline, so this pattern isn't cleaned up...
That would perhaps better, but it will again have some compile time impact.
Reviewed By: RKSimon
Differential Revision: https://reviews.llvm.org/D106010
