DSE has some extra logic to determine the write location of library
calls like str*cpy and str*cat. This patch moves the logic to a new
MemoryLocation:getForDest variant, which takes a call and TLI.
This patch should be NFC, because no other places take advantage of the
new helper yet.
Suggested by @reames post-commit 7eec832def.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D114872
This allows for better optimization of 'stores-of-existing-values' and
possibly helps passes further down the pipeline.
Reviewed By: asbirlea
Differential Revision: https://reviews.llvm.org/D113712
Using the optimized access enables additional optimizations in cases
where the defining access is a non-aliasing store.
Alternatively we could also walk upwards and skip non-aliasing defs
here, but my experiments so far showed that this will noticeably
increase compile-time for little extra gain compared to just using the
optimized access.
Improvements of dse.NumRedundantStores on MultiSource/CINT2006/CPF2006
on X86 with -O3:
test-suite...-typeset/consumer-typeset.test 1.00 76.00 7500.0%
test-suite.../Benchmarks/Bullet/bullet.test 3.00 12.00 300.0%
test-suite...006/453.povray/453.povray.test 3.00 6.00 100.0%
test-suite...telecomm-gsm/telecomm-gsm.test 1.00 2.00 100.0%
test-suite...ediabench/gsm/toast/toast.test 1.00 2.00 100.0%
test-suite...marks/7zip/7zip-benchmark.test 1.00 2.00 100.0%
test-suite...ications/JM/lencod/lencod.test 7.00 10.00 42.9%
test-suite...6/464.h264ref/464.h264ref.test 6.00 8.00 33.3%
test-suite...ications/JM/ldecod/ldecod.test 6.00 7.00 16.7%
test-suite...006/447.dealII/447.dealII.test 33.00 33.00 0.0%
test-suite...6/471.omnetpp/471.omnetpp.test NaN 1.00 nan%
test-suite...006/450.soplex/450.soplex.test NaN 2.00 nan%
test-suite.../CINT2006/403.gcc/403.gcc.test NaN 7.00 nan%
test-suite...lications/ClamAV/clamscan.test NaN 1.00 nan%
test-suite...CI_Purple/SMG2000/smg2000.test NaN 3.00 nan%
Follow-up to D111727.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D112315
I'm not sure whether this can cause any actual non-determinism,
but at least it makes the DSE debug log non-deterministic, which
makes it harder to debug other non-determinism issues.
This patch extends the code that walks memory defs upwards to find
clobbering accesses to also try to optimize the clobbering defining
access.
We should be able to find set the optimized access of our starting def
(KillingDef), if the following holds:
1. It is the first call of getDomMemoryDef for KillingDef (so Current
== KillingDef->getDefiningAccess().
2. No potentially aliasing defs are skipped.
Then if a (partly) aliasing def is encountered, it can be used as
optimized access for KillingDef. No further optimizations can be
applied to KillingDef.
I'd appreciate a careful look, as the existing documentation is not too
clear on what is expected for optimized accesses.
The motivation for this patch is to use the optimized accesses to cover
more cases of redundant stores as follow-up to D111727.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D112313
Add OR_None code to indicate that there is no overwrite. This has no any effect for current uses but will be used in one of the next patches building support for PHI translation.
Reviewed By: fhahn
Differential Revision: https://reviews.llvm.org/D105098
The functionality of hasAnalyzableMemoryWrite() is effectively
subsumed by getLocForWriteEx(), which will return None if the
instruction is not analyzable. The implementations don't match
exactly (e.g. getLocForWriteEx() does not limit non-calls to
stores), but in conjunction with the isRemovable() check, it ends
up being the same.
This implements nearly the same logic as getLocForWriteEx(), and
is only used in one place. In that context, we should also know
that getLocForWriteEx() returns a non-None result. As such,
consolidate everything to use one function.
This patch adds support to remove stores that write the same value
as earlier memesets.
It uses isOverwrite to check that a memset completely overwrites a later
store. The candidate store must store the same bytewise value as the
byte stored by the memset.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D112321
That's https://reviews.llvm.org/D90328 follow-up.
This change eliminates writes to variables where the value that is being written is already stored in the variable.
This achieves the goal by looping through all memory definitions in the current state and getting defining access from each of them.
When there is defining access where the write instruction is identical to the original instruction it will remove this redundant write.
For example:
void f() {
x = 1;
if foo() {
x = 1;
g();
} else {
h();
}
}
void g();
void h();
The second x=1 will be eliminated since it is rewriting 1 to x. This pass will produce this:
void f() {
x = 1;
if foo() {
g();
} else {
h();
}
}
void g();
void h();
Differential Revision: https://reviews.llvm.org/D111727
The initial MemoryAccess *Current assignment is never used, and all other uses are initialized/used within the worklist loop (and not across multiple iterations) - so move the variable internal to the loop.
Fixes scan-build unused assignment warning.
Transformation from malloc+memset to calloc is always correct and in many situations
it brings significant observable benefits in terms of execution speed and memory consumption [1][2].
Unfortunately there are cases when producing calloc cause performance drops [3].
As discussed here: https://reviews.llvm.org/D103009 it's possible to differentiate between those 2 scenarios.
If optimizer is able to prove that after malloc call it's _very_ likely to reach memset branch then after
calloc emission we shouldn't observe any performance hits. Therefore finding "null pointer check" pattern
before memset basic block sounds like good justification for performing transformation.
Also that method was already suggested by GCC folks [4]. Main reason for change is that for now
to be safe we check for post dominance relation which is way too conservative approach making transformation
"almost" disabled in practice. This patch tends to enable transformation again but with extra care.
[1] https://stackoverflow.com/questions/2688466/why-mallocmemset-is-slower-than-calloc
[2] https://vorpus.org/blog/why-does-calloc-exist/
[3] http://smalldatum.blogspot.com/2017/11/a-new-optimization-in-gcc-5x-and-mysql.html
[4] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83022
Differential Revision: https://reviews.llvm.org/D110021
As it contains a self-reference, the default copy/move ctors
would not be safe.
Move the DSEState::get() method into the ctor to make sure no move
occurs here even without NRVO.
This is a speculative fix for test failures on
llvm-clang-x86_64-expensive-checks-win.
This is a followup to D109844 (and alternative to D109907), which
integrates the new "earliest escape" tracking into AliasAnalysis.
This is done by replacing the pre-existing context-free capture
cache in AAQueryInfo with a replaceable (virtual) object with two
implementations: The SimpleCaptureInfo implements the previous
behavior (check whether object is captured at all), while
EarliestEscapeInfo implements the new behavior from DSE.
This combines the "earliest escape" analysis with the full power of
BasicAA: It subsumes the call handling from D109907, considers a
wider range of escape sources, and works with AA recursion. The
compile-time cost is slightly higher than with D109907.
Differential Revision: https://reviews.llvm.org/D110368
It is sufficient that the object has not been captured before the
load that produces the pointer we're loading. A capture after that
can not affect the already loaded pointer.
This is small part of D110368 applied separately.
This reverts the revert commit df56fc6ebb.
This version of the patch adjusts the location where the EarliestEscapes
cache is cleared when an instruction gets removed. The earliest escaping
instruction does not have to be a memory instruction.
It could be a ptrtoint instruction like in the added test
@earliest_escape_ptrtoint, which subsequently gets removed. We need to
invalidate the EarliestEscape entry referring to the ptrtoint when
deleting it.
This fixes the crash mentioned in
https://bugs.chromium.org/p/chromium/issues/detail?id=1252762#c6
At the moment, DSE only considers whether a pointer may be captured at
all in a function. This leads to cases where we fail to remove stores to
local objects because we do not check if they escape before potential
read-clobbers or after.
Doing context-sensitive escape queries in isReadClobber has been removed
a while ago in d1a1cce5b1 to save compile-time. See PR50220 for more
context.
This patch introduces a new capture tracker, which keeps track of the
'earliest' capture. An instruction A is considered earlier than instruction
B, if A dominates B. If 2 escapes do not dominate each other, the
terminator of the common dominator is chosen. If not all uses cannot be
analyzed, the earliest escape is set to the first instruction in the
function entry block.
If the query instruction dominates the earliest escape and is not in a
cycle, then pointer does not escape before the query instruction.
This patch uses this information when checking if a load of a loaded
underlying object may alias a write to a stack object. If the stack
object does not escape before the load, they do not alias.
I will share a follow-up patch to also use the information for call
instructions to fix PR50220.
In terms of compile-time, the impact is low in general,
NewPM-O3: +0.05%
NewPM-ReleaseThinLTO: +0.05%
NewPM-ReleaseLTO-g: +0.03
with the largest change being tramp3d-v4 (+0.30%)
http://llvm-compile-time-tracker.com/compare.php?from=1a3b3301d7aa9ab25a8bdf045c77298b087e3930&to=bc6c6899cae757c3480f4ad4874a76fc1eafb0be&stat=instructions
Compared to always computing the capture information on demand, we get
the following benefits from the caching:
NewPM-O3: -0.03%
NewPM-ReleaseThinLTO: -0.08%
NewPM-ReleaseLTO-g: -0.04%
The biggest speedup is tramp3d-v4 (-0.21%).
http://llvm-compile-time-tracker.com/compare.php?from=0b0c99177d1511469c633282ef67f20c851f58b1&to=bc6c6899cae757c3480f4ad4874a76fc1eafb0be&stat=instructions
Overall there is a small, but noticeable benefit from caching. I am not
entirely sure if the speedups warrant the extra complexity of caching.
The way the caching works also means that we might miss a few cases, as
it is less precise. Also, there may be a better way to cache things.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D109844
First (and biggest) change is to use "Killing/Dead" in place of "Later/Earlier" base for names in DSE. For example, [Maybe]DeadLoc - is a location killed by KillingI instruction. I believe such names are more descriptive and easy to understand than current ones.
Second, there are inconsistencies in naming where different names are used for the same thing. Fixed that too.
Third, reordered parameters of isPartialOverwrite, tryToMergePartialOverlappingStores, isOverwrite to make them consistent between each other. This greatly reduces potential mistakes.
Reviewed By: fhahn
Differential Revision: https://reviews.llvm.org/D106947
Another simple cleanups set in DSE. CheckCache is removed since 1f1145006b and in consequence KnownNoReads is useless.
Also update description of MemorySSAScanLimit which default value is 150 instead 100.
Differential Revision: https://reviews.llvm.org/D107812
With 'for' loop there is is a single place where 'Current' is adjusted. It helps to avoid copy paste and makes a bit easy to understand overall loop controll flow.
Reviewed By: fhahn
Differential Revision: https://reviews.llvm.org/D101044
For the start shortening optimization, always use a i8 type for
the GEP, as it is a raw offset calculation.
Handling of non-i8* memset/memcpy arguments requires insertion
of casts. These cases were previously miscompiled, as the offset
calculation was performed on the wrong type.
DSE will currently only remove stores in the same block unless they can
be guaranteed to be loop invariant. This expands that to any stores that
are in the same Loop, at the same loop level. This should still account
for where AA/MSSA will not handle aliasing between loops, but allow the
dead stores to be removed where they overlap in the same loop iteration.
It requires adding loop info to DSE, but that looks fairly harmless.
The test case this helps is from code like this, which can come up in
certain matrix operations:
for(i=..)
dst[i] = 0;
for(j=..)
dst[i] += src[i*n+j];
After LICM, this becomes:
for(i=..)
dst[i] = 0;
sum = 0;
for(j=..)
sum += src[i*n+j];
dst[i] = sum;
The first store is dead, and with this patch is now removed.
Differntial Revision: https://reviews.llvm.org/D100464
DSE will currently only remove stores in the same block unless they can
be guaranteed to be loop invariant. This expands that to any stores that
are in the same Loop, at the same loop level. This should still account
for where AA/MSSA will not handle aliasing between loops, but allow the
dead stores to be removed where they overlap in the same loop iteration.
It requires adding loop info to DSE, but that looks fairly harmless.
The test case this helps is from code like this, which can come up in
certain matrix operations:
for(i=..)
dst[i] = 0;
for(j=..)
dst[i] += src[i*n+j];
After LICM, this becomes:
for(i=..)
dst[i] = 0;
sum = 0;
for(j=..)
sum += src[i*n+j];
dst[i] = sum;
The first store is dead, and with this patch is now removed.
Differntial Revision: https://reviews.llvm.org/D100464
Currently all AA analyses marked as preserved are stateless, not taking
into account their dependent analyses. So there's no need to mark them
as preserved, they won't be invalidated unless their analyses are.
SCEVAAResults was the one exception to this, it was treated like a
typical analysis result. Make it like the others and don't invalidate
unless SCEV is invalidated.
Reviewed By: asbirlea
Differential Revision: https://reviews.llvm.org/D102032
This moves the isOverwrite function into the DSEState so that it can
share the analyses and members from the state.
A few extra loop tests were also added to test stores in and around
multi block loops for D100464.
Solves PR11896
As noted, this can be improved futher (calloc -> malloc) in some cases. But for know, this is the first step.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D101391
Add an ability to store `Offset` between partially aliased location. Use this
storage within returned `ResultAlias` instead of caching it in `AAQueryInfo`.
Reviewed By: asbirlea
Differential Revision: https://reviews.llvm.org/D98718
The isOverwrite function is making sure to identify if two stores
are fully overlapping and ideally we would like to identify all the
instances of OW_Complete as they'll yield possibly killable stores.
The current implementation is incapable of spotting instances where
the earlier store is offsetted compared to the later store, but
still fully overlapped. The limitation seems to lie on the
computation of the base pointers with the
GetPointerBaseWithConstantOffset API that often yields different
base pointers even if the stores are guaranteed to partially overlap
(e.g. the alias analysis is returning AliasResult::PartialAlias).
The patch relies on the offsets computed and cached by BatchAAResults
(available after D93529) to determine if the offsetted overlapping
is OW_Complete.
Differential Revision: https://reviews.llvm.org/D97676
Currently DSE misses cases where the size is a non-const IR value, even
if they match. For example, this means that llvm.memcpy/llvm.memset
calls are not eliminated, even if they write the same number of bytes.
This patch extends isOverwite to try to get IR values for the number of
bytes written from the analyzed instructions. If the values match,
alias checks are performed and the result is returned.
At the moment this only covers llvm.memcpy/llvm.memset. In the future,
we may enable MemoryLocation to also track variable sizes, but this
simple approach should allow us to cover the important cases in DSE.
Reviewed By: asbirlea
Differential Revision: https://reviews.llvm.org/D98284
The MemorySSA-based implementation has been enabled without issue
for a while now, so keeping the old implementation around doesn't
seem useful anymore. This drops the MemDep-based implementation.
Differential Revision: https://reviews.llvm.org/D97877
This is an attempt to improve handling of partial overlaps in case of unaligned begin\end.
Existing implementation just bails out if it encounters such cases. Even when it doesn't I believe existing code checking alignment constraints is not quite correct. It tries to ensure alignment of the "later" start/end offset while should be preserving relative alignment between earlier and later start/end.
The idea behind the change is simple. When start/end is not aligned as we wish instead of bailing out let's adjust it as necessary to get desired alignment.
I'll update with performance results as measured by the test-suite...it's still running...
Reviewed By: fhahn
Differential Revision: https://reviews.llvm.org/D93530
Florian Hahn