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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187868 91177308-0d34-0410-b5e6-96231b3b80d8
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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172453 91177308-0d34-0410-b5e6-96231b3b80d8
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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169133 91177308-0d34-0410-b5e6-96231b3b80d8
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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168996 91177308-0d34-0410-b5e6-96231b3b80d8
This silences literally dozens of analyzer warnings on LLVM (since DenseMap
is such a commonly-used class).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164438 91177308-0d34-0410-b5e6-96231b3b80d8
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. =/
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159648 91177308-0d34-0410-b5e6-96231b3b80d8
Based on review discussion of r158638 with Chandler Carruth, Tobias von Koch, and Duncan Sands and a -Wmaybe-uninitialized warning from GCC.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158685 91177308-0d34-0410-b5e6-96231b3b80d8
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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158641 91177308-0d34-0410-b5e6-96231b3b80d8
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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158639 91177308-0d34-0410-b5e6-96231b3b80d8
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. =]
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158638 91177308-0d34-0410-b5e6-96231b3b80d8
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... =/
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158586 91177308-0d34-0410-b5e6-96231b3b80d8
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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158585 91177308-0d34-0410-b5e6-96231b3b80d8
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 :)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157539 91177308-0d34-0410-b5e6-96231b3b80d8
When the hash function uses object pointers all free entries eventually
become tombstones as they are used at least once, regardless of the size.
DenseMap cannot function with zero empty keys, so it double size to get
get ridof the tombstones.
However DenseMap never shrinks automatically unless it is cleared, so
the net result is that certain tables grow infinitely.
The solution is to make a fresh copy of the table without tombstones
instead of doubling size, by simply calling grow with the current size.
Patch by José Fonseca!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128564 91177308-0d34-0410-b5e6-96231b3b80d8
This makes lookup slightly more expensive but it's worth it, unused
DenseMaps are common in LLVM code apparently.
1% speedup on clang -O3 bzip2.c
4% speedup on clang -O3 oggenc.c (Release build of clang on i386/linux)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127088 91177308-0d34-0410-b5e6-96231b3b80d8
