We can often end up with conditional stores that cannot be speculated. They can come from fairly simple, idiomatic code:
if (c & flag1)
*a = x;
if (c & flag2)
*a = y;
...
There is no dominating or post-dominating store to a, so it is not legal to move the store unconditionally to the end of the sequence and cache the intermediate result in a register, as we would like to.
It is, however, legal to merge the stores together and do the store once:
tmp = undef;
if (c & flag1)
tmp = x;
if (c & flag2)
tmp = y;
if (c & flag1 || c & flag2)
*a = tmp;
The real power in this optimization is that it allows arbitrary length ladders such as these to be completely and trivially if-converted. The typical code I'd expect this to trigger on often uses binary-AND with constants as the condition (as in the above example), which means the ending condition can simply be truncated into a single binary-AND too: 'if (c & (flag1|flag2))'. As in the general case there are bitwise operators here, the ladder can often be optimized further too.
This optimization involves potentially increasing register pressure. Even in the simplest case, the lifetime of the first predicate is extended. This can be elided in some cases such as using binary-AND on constants, but not in the general case. Threading 'tmp' through all branches can also increase register pressure.
The optimization as in this patch is enabled by default but kept in a very conservative mode. It will only optimize if it thinks the resultant code should be if-convertable, and additionally if it can thread 'tmp' through at least one existing PHI, so it will only ever in the worst case create one more PHI and extend the lifetime of a predicate.
This doesn't trigger much in LNT, unfortunately, but it does trigger in a big way in a third party test suite.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252051 91177308-0d34-0410-b5e6-96231b3b80d8
This was breaking the modules build and is being reverted while we reach consensus on the right way to solve this layering problem. This reverts commit r251785.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252040 91177308-0d34-0410-b5e6-96231b3b80d8
Intended to make later changes simpler. Exposes
`getBundleOperandsStartIndex` and `getBundleOperandsEndIndex`, and uses
them for the computation in `getNumTotalBundleOperands`.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252037 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
The goal of this pass is to perform store-to-load forwarding across the
backedge of a loop. E.g.:
for (i)
A[i + 1] = A[i] + B[i]
=>
T = A[0]
for (i)
T = T + B[i]
A[i + 1] = T
The pass relies on loop dependence analysis via LoopAccessAnalisys to
find opportunities of loop-carried dependences with a distance of one
between a store and a load. Since it's using LoopAccessAnalysis, it was
easy to also add support for versioning away may-aliasing intervening
stores that would otherwise prevent this transformation.
This optimization is also performed by Load-PRE in GVN without the
option of multi-versioning. As was discussed with Daniel Berlin in
http://reviews.llvm.org/D9548, this is inferior to a more loop-aware
solution applied here. Hopefully, we will be able to remove some
complexity from GVN/MemorySSA as a consequence.
In the long run, we may want to extend this pass (or create a new one if
there is little overlap) to also eliminate loop-indepedent redundant
loads and store that *require* versioning due to may-aliasing
intervening stores/loads. I have some motivating cases for store
elimination. My plan right now is to wait for MemorySSA to come online
first rather than using memdep for this.
The main motiviation for this pass is the 456.hmmer loop in SPECint2006
where after distributing the original loop and vectorizing the top part,
we are left with the critical path exposed in the bottom loop. Being
able to promote the memory dependence into a register depedence (even
though the HW does perform store-to-load fowarding as well) results in a
major gain (~20%). This gain also transfers over to x86: it's
around 8-10%.
Right now the pass is off by default and can be enabled
with -enable-loop-load-elim. On the LNT testsuite, there are two
performance changes (negative number -> improvement):
1. -28% in Polybench/linear-algebra/solvers/dynprog: the length of the
critical paths is reduced
2. +2% in Polybench/stencils/adi: Unfortunately, I couldn't reproduce this
outside of LNT
The pass is scheduled after the loop vectorizer (which is after loop
distribution). The rational is to try to reuse LAA state, rather than
recomputing it. The order between LV and LLE is not critical because
normally LV does not touch scalar st->ld forwarding cases where
vectorizing would inhibit the CPU's st->ld forwarding to kick in.
LoopLoadElimination requires LAA to provide the full set of dependences
(including forward dependences). LAA is known to omit loop-independent
dependences in certain situations. The big comment before
removeDependencesFromMultipleStores explains why this should not occur
for the cases that we're interested in.
Reviewers: dberlin, hfinkel
Subscribers: junbuml, dberlin, mssimpso, rengolin, sanjoy, llvm-commits
Differential Revision: http://reviews.llvm.org/D13259
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252017 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
The functions use LAI and MemoryDepChecker classes so they need to be
defined after those definitions outside of the Dependence class.
Will be used by the LoopLoadElimination pass.
Reviewers: hfinkel
Subscribers: rengolin, llvm-commits
Differential Revision: http://reviews.llvm.org/D13257
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252015 91177308-0d34-0410-b5e6-96231b3b80d8
A profile of an LTO link of Chrome revealed that we were spending some
~30-50% of execution time in the function Constant::getRelocationInfo(),
which is called from TargetLoweringObjectFile::getKindForGlobal() and in turn
from TargetMachine::getNameWithPrefix().
It turns out that we only need the result of getKindForGlobal() when
targeting Mach-O, so this change moves the relevant part of the logic to
TargetLoweringObjectFileMachO.
NFCI.
Differential Revision: http://reviews.llvm.org/D14168
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252014 91177308-0d34-0410-b5e6-96231b3b80d8
Introduce DIPrinter which takes care of rendering DILineInfo and
friends. This allows LLVMSymbolizer class to return a structured data
instead of plain std::strings.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251989 91177308-0d34-0410-b5e6-96231b3b80d8
Make printDILineInfo and friends responsible for just rendering the
contents of the structures, demangling should actually be performed
earlier, when we have the information about the originating
SymbolizableModule at hand.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251981 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
When the dependence distance in zero then we have a loop-independent
dependence from the earlier to the later access.
No current client of LAA uses forward dependences so other than
potentially hitting the MaxDependences threshold earlier, this change
shouldn't affect anything right now.
This and the previous patch were tested together for compile-time
regression. None found in LNT/SPEC.
Reviewers: hfinkel
Subscribers: rengolin, llvm-commits
Differential Revision: http://reviews.llvm.org/D13255
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251973 91177308-0d34-0410-b5e6-96231b3b80d8
We now create them as they are found and use higher level APIs.
This is a step in avoiding creating unnecessary sections.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251958 91177308-0d34-0410-b5e6-96231b3b80d8
Bypassing LLVM for this has a number of benefits:
1) Laziness support becomes asm-syntax agnostic (previously lazy jitting didn't
work on Windows as the resolver block was in Darwin asm).
2) For cross-process JITs, it allows resolver blocks and trampolines to be
emitted directly in the target process, reducing cross process traffic.
3) It should be marginally faster.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251933 91177308-0d34-0410-b5e6-96231b3b80d8
When push instructions are being used to pass function arguments on
the stack, and either EH or debugging are enabled, we need to generate
.cfi_adjust_cfa_offset directives appropriately. For (synch) EH, it is
enough for the CFA offset to be correct at every call site, while
for debugging we want to be correct after every push.
Darwin does not support this well, so don't use pushes whenever it
would be required.
Differential Revision: http://reviews.llvm.org/D13767
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251904 91177308-0d34-0410-b5e6-96231b3b80d8
ScheduleDAGInstrs doesn't behave differently before or after register
allocation. It was only used in a method of MachineSchedulerBase which
behaved differently in MachineScheduler/PostMachineScheduler. Change
this to let MachineScheduler/PostMachineScheduler just pass in a
parameter to that function.
The order of the LiveIntervals* and bool RemoveKillFlags paramters have
been switched to make out-of-tree code fail instead of unintentionally
passing a value intended for the IsPostRA flag to the (previously
following and default initialized) RemoveKillFlags.
Differential Revision: http://reviews.llvm.org/D14245
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251883 91177308-0d34-0410-b5e6-96231b3b80d8
This restores commit r251837, with the new library dependence added to
llvm-link/Makefile to address bot failures.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251866 91177308-0d34-0410-b5e6-96231b3b80d8
This reverts commit r251837, due to a number of bot failures of the form:
/home/grosser/buildslave/perf-x86_64-penryn-O3-polly-fast/llvm.obj/tools/llvm-link/Release+Asserts/llvm-link.o:llvm-link.cpp:function
loadIndex(llvm::LLVMContext&, llvm::Module const*): error: undefined
reference to
'llvm::object::FunctionIndexObjectFile::create(llvm::MemoryBufferRef,
llvm::LLVMContext&, llvm::Module const*, bool)'
/home/grosser/buildslave/perf-x86_64-penryn-O3-polly-fast/llvm.obj/tools/llvm-link/Release+Asserts/llvm-link.o:llvm-link.cpp:function
loadIndex(llvm::LLVMContext&, llvm::Module const*): error: undefined
reference to 'llvm::object::FunctionIndexObjectFile::takeIndex()'
I'm not sure why these are happening - I added Object to the requred
libraries in tools/llvm-link/LLVMBuild.txt and the LLVM_LINK_COMPONENTS
in tools/llvm-link/CMakeLists.txt. Confirmed for my build that these
symbols come out of libLLVMObject.a. What am I missing?
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251841 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
Support for necessary linkage changes and symbol renaming during
ThinLTO function importing.
Also includes llvm-link support for manually importing functions
and associated llvm-link based tests.
Note that this does not include support for intelligently importing
metadata, which is currently imported duplicate times. That support will
be in the follow-on patch, and currently is ignored by the tests.
Reviewers: dexonsmith, joker.eph, davidxl
Subscribers: tobiasvk, tejohnson, llvm-commits
Differential Revision: http://reviews.llvm.org/D13515
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251837 91177308-0d34-0410-b5e6-96231b3b80d8
Remove code that was assuming that this would never work.
Thanks to Colin LeMahie for finding and diagnosing the bug.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251818 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
SCEV Predicates represent conditions that typically cannot be derived from
static analysis, but can be used to reduce SCEV expressions to forms which are
usable for different optimizers.
ScalarEvolution now has the rewriteUsingPredicate method which can simplify a
SCEV expression using a SCEVPredicateSet. The normal workflow of a pass using
SCEVPredicates would be to hold a SCEVPredicateSet and every time assumptions
need to be made a new SCEV Predicate would be created and added to the set.
Each time after calling getSCEV, the user will call the rewriteUsingPredicate
method.
We add two types of predicates
SCEVPredicateSet - implements a set of predicates
SCEVEqualPredicate - tests for equality between two SCEV expressions
We use the SCEVEqualPredicate to re-implement stride versioning. Every time we
version a stride, we will add a SCEVEqualPredicate to the context.
Instead of adding specific stride checks, LoopVectorize now adds a more
generic SCEV check.
We only need to add support for this in the LoopVectorizer since this is the
only pass that will do stride versioning.
Reviewers: mzolotukhin, anemet, hfinkel, sanjoy
Subscribers: sanjoy, hfinkel, rengolin, jmolloy, llvm-commits
Differential Revision: http://reviews.llvm.org/D13595
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251800 91177308-0d34-0410-b5e6-96231b3b80d8
Instead of rolling our own min/max matching code (which is notoriously
hard to get completely right), use ValueTracking's instead.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251785 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
The new function sys::path::user_cache_directory tries to discover
a directory suitable for cache storage for current system user.
On Windows and Darwin it returns a path to system-specific user cache directory.
On Linux it follows XDG Base Directory Specification, what is:
- use non-empty $XDG_CACHE_HOME env var,
- use $HOME/.cache.
Reviewers: chapuni, aaron.ballman, rafael
Subscribers: rafael, aaron.ballman, llvm-commits
Differential Revision: http://reviews.llvm.org/D13801
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251784 91177308-0d34-0410-b5e6-96231b3b80d8
1. Added a set of public interfaces in InstrProfRecord
class to access (read/write) value profile data.
2. Changed IndexedProfile reader and writer code to
use the newly defined interfaces and hide implementation
details.
3. Added a couple of unittests for value profiling:
- Test new interfaces to get and set value profile data
- Test value profile data merging with various scenarios.
No functional change is expected. The new interfaces will also
make it possible to change on-disk format of value prof data
to be more compact (to be submitted).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251771 91177308-0d34-0410-b5e6-96231b3b80d8
We never need to pass end(). This will also remove some complication
once we start adding error checking.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251758 91177308-0d34-0410-b5e6-96231b3b80d8
This is a bit ugly, but has a few advantages:
* Archive is now easy to copy since there is no Archive -> Child -> Archive
loop.
* It makes it clear that we already checked for errors when finding the Child
data.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251750 91177308-0d34-0410-b5e6-96231b3b80d8
underlying memory, and will automatically release it on destruction.
Use this to tidy up the orc::IndirectStubsInfo class.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251731 91177308-0d34-0410-b5e6-96231b3b80d8
This is a really straightforward port. Also adds a test for the pass,
since it only seemed to be tested tangentially before.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251726 91177308-0d34-0410-b5e6-96231b3b80d8
