This assumes that
a) finding the bucket containing the value is LIKELY
b) finding an empty bucket is LIKELY
c) growing the table is UNLIKELY
I also switched the a) and b) cases for SmallPtrSet as we seem to use
the set mostly more for insertion than for checking existence.
In a simple benchmark consisting of 2^21 insertions of 2^20 unique
pointers into a DenseMap or SmallPtrSet a few percent speedup on average,
but nothing statistically significant.
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DenseSet used to be implemented as DenseMap<Key, char>, which usually doubled
the memory footprint of the map. Now we use a compressed set so the second
element uses no memory at all. This required some surgery on DenseMap as
all accesses to the bucket now have to go through methods; this should
have no impact on the behavior of DenseMap though. The new default bucket
type for DenseMap is a slightly extended std::pair as we expose it through
DenseMap's iterator and don't want to break any existing users.
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Various places in LLVM assume that container size and count are unsigned
and do not use the container size_type. Therefore they break compilation
(or possibly executation) for LP64 systems where size_t is 64 bit while
unsigned is still 32 bit.
If we'll ever that many items in the container size_type could be made
size_t for a specific containers after reviweing its other uses.
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only 1/0 result like std::set. Some of the LLVM ADT already return unsigned
count(), while others still return bool count().
In continuation to r197879, this patch modifies DenseMap, DenseSet,
ScopedHashTable, ValueMap:: count() to return size_type instead of bool,
1 instead of true and 0 instead of false.
size_type is typedef-ed locally within each class to size_t.
http://reviews.llvm.org/D4018
Reviewed by dblaikie.
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Prevent a crash in the SmallDenseMap copy constructor whenever the other
map is not in small mode.
<rdar://problem/14292693>
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This problem was found and fixed by José Fonseca in March 2011 for
SmallPtrSet, committed r128566. But as far as I can tell, all other
llvm hash tables retain the same problem: the bucket count can grow
without bound while size() remains near constant by repeated
insert/erase cycles that tend to fill the container with tombstones.
Here is a demo that has been reduced to a trivial case:
int
main()
{
llvm::DenseSet<unsigned> d;
for (unsigned i = 0; i < 0xFFFFFFF; ++i)
{
d.insert(i);
d.erase(i);
}
}
While the container size() never grows above 1, the bucket count grows
like this:
nb = 64
nb = 128
nb = 256
nb = 512
nb = 1024
nb = 2048
nb = 4096
nb = 8192
nb = 16384
nb = 32768
nb = 65536
nb = 131072
nb = 262144
nb = 524288
nb = 1048576
nb = 2097152
nb = 4194304
nb = 8388608
nb = 16777216
nb = 33554432
nb = 67108864
nb = 134217728
nb = 268435456
The above program currently consumes a few GB ram. This patch brings
the memory consumption down by several orders of magnitude, and keeps
the bucket count at 64 for the above test.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193689 91177308-0d34-0410-b5e6-96231b3b80d8
lld has a hashtable with StringRef keys; it needs to iterate over the keys in
*insertion* order. This is currently implemented as std::vector<StringRef> +
DenseMap<StringRef, T>. This will probably need a proper
DenseMapInfo<StringRef> if we don't want to lose memory/performance by
migrating to a different data structure.
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for StringRef with a StringMap
The bug is that the empty key compares equal to the tombstone key.
Also added an assertion to DenseMap to catch similar bugs in future.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187866 91177308-0d34-0410-b5e6-96231b3b80d8
Use the existing move implementation of the internal DenseMap::InsertIntoBucket
method to provide a user-facing move insert method.
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With DenseMapInfo<Enum>, it is miscompiled on g++-4.4.
static inline Enum getEmptyKey() { return Enum(<arbitrary int/unsigned value>); }
isEauql(getEmptyKey(), ...)
The compiler mis-assumes the return value is not aliased to Enum.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171600 91177308-0d34-0410-b5e6-96231b3b80d8
AKA: Recompile *ALL* the source code!
This one went much better. No manual edits here. I spot-checked for
silliness and grep-checked for really broken edits and everything seemed
good. It all still compiles. Yell if you see something that looks goofy.
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Rationale:
1) This was the name in the comment block. ;]
2) It matches Clang's __has_feature naming convention.
3) It matches other compiler-feature-test conventions.
Sorry for the noise. =]
I've also switch the comment block to use a \brief tag and not duplicate
the name.
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This silences literally dozens of analyzer warnings on LLVM (since DenseMap
is such a commonly-used class).
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some, and allows the routine to be inlined into common callers. The
various bits that hit this code in their hotpath seem slightly lower on
the profile, but I can't really measure a performance improvement as
everything seems to still be bottlenecked on likely cache misses. =/
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Based on review discussion of r158638 with Chandler Carruth, Tobias von Koch, and Duncan Sands and a -Wmaybe-uninitialized warning from GCC.
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SmallDenseMap::swap.
First, make it parse cleanly. Yay for uninstantiated methods.
Second, make the inline-buckets case work correctly. This is way
trickier than it should be due to the uninitialized values in empty and
tombstone buckets.
Finally fix a few typos that caused construction/destruction mismatches
in the counting unittest.
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destruction and fix a bug in SmallDenseMap they caught.
This is kind of a poor-man's version of the testing that just adds the
addresses to a set on construction and removes them on destruction. We
check that double construction and double destruction don't occur.
Amusingly enough, this is enough to catch a lot of SmallDenseMap issues
because we spend a lot of time with fixed stable addresses in the inline
buffer.
The SmallDenseMap bug fix included makes grow() not double-destroy in
some cases. It also fixes a FIXME there, the code was pretty crappy. We
now don't have any wasted initialization, but we do move the entries in
inline bucket array an extra time. It's probably a better tradeoff, and
is much easier to get correct.
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implementation.
This type includes an inline bucket array which is used initially. Once
it is exceeded, an array of 64 buckets is allocated on the heap. The
bucket count grows from there as needed. Some highlights of this
implementation:
- The inline buffer is very carefully aligned, and so supports types
with alignment constraints.
- It works hard to avoid aliasing issues.
- Supports types with non-trivial constructors, destructors, copy
constructions, etc. It works reasonably hard to minimize copies and
unnecessary initialization. The most common initialization is to set
keys to the empty key, and so that should be fast if at all possible.
This class has a performance / space trade-off. It tries to optimize for
relatively small maps, and so packs the inline bucket array densely into
the object. It will be marginally slower than a normal DenseMap in a few
use patterns, so it isn't appropriate everywhere.
The unit tests for DenseMap have been generalized a bit to support
running over different map implementations in addition to different
key/value types. They've then been automatically extended to cover the
new container through the magic of GoogleTest's typed tests.
All of this is still a bit rough though. I'm going to be cleaning up
some aspects of the implementation, documenting things better, and
adding tests which include non-trivial types. As soon as I'm comfortable
with the correctness, I plan to switch existing users of SmallMap over
to this class as it is already more correct w.r.t. construction and
destruction of objects iin the map.
Thanks to Benjamin Kramer for all the reviews of this and the lead-up
patches. That said, more review on this would really be appreciated. As
I've noted a few times, I'm quite surprised how hard it is to get the
semantics for a hashtable-based map container with a small buffer
optimization correct. =]
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rather than the base class. Add a pile of boilerplate to indirect around
this.
This is pretty ugly, but it allows the super class to change the
representation of these values, which will be key for doing
a SmallDenseMap.
Suggestions on better method structuring / naming are welcome, but keep
in mind that SmallDenseMap won't have an 'unsigned' member to expose
a reference to... =/
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and a derived class that provides the allocation and growth strategy.
This is the first (and biggest) step toward building a SmallDenseMap
that actually behaves exactly the same as DenseMap, and supports all the
same types and interface points with the same semantics.
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The only missing part is insert(), which uses a pair of parameters and I haven't
figured out how to convert it to rvalue references. It's now possible to use a
DenseMap with std::unique_ptr values :)
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