[llvm] r213084 - ADT: Fix MapVector::erase()

[Yaron Keren]

Thanks!

Would it make sense to have erase(Key) in addition to erase(Iterator) ?

Yaron



2014-07-15 21:32 GMT+03:00 Duncan P. N. Exon Smith <dexonsmith at apple.com>:

> Author: dexonsmith
> Date: Tue Jul 15 13:32:30 2014
> New Revision: 213084
>
> URL: http://llvm.org/viewvc/llvm-project?rev=213084&view=rev
> Log:
> ADT: Fix MapVector::erase()
>
> Actually update the changed indexes in the map portion of `MapVector`
> when erasing from the middle.  Add a unit test that checks for this.
>
> Note that `MapVector::erase()` is a linear time operation (it was and
> still is).  I'll commit a new method in a moment called
> `MapVector::remove_if()` that deletes multiple entries in linear time,
> which should be slightly less painful.
>
> Modified:
>     llvm/trunk/docs/ProgrammersManual.rst
>     llvm/trunk/include/llvm/ADT/MapVector.h
>     llvm/trunk/unittests/ADT/MapVectorTest.cpp
>
> Modified: llvm/trunk/docs/ProgrammersManual.rst
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/ProgrammersManual.rst?rev=213084&r1=213083&r2=213084&view=diff
>
> ==============================================================================
> --- llvm/trunk/docs/ProgrammersManual.rst (original)
> +++ llvm/trunk/docs/ProgrammersManual.rst Tue Jul 15 13:32:30 2014
> @@ -1442,7 +1442,7 @@ iteration over maps of pointers.
>
>  It is implemented by mapping from key to an index in a vector of key,value
>  pairs.  This provides fast lookup and iteration, but has two main
> drawbacks: The
> -key is stored twice and it doesn't support removing elements.
> +key is stored twice and removing elements takes linear time.
>
>  .. _dss_inteqclasses:
>
>
> Modified: llvm/trunk/include/llvm/ADT/MapVector.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/MapVector.h?rev=213084&r1=213083&r2=213084&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/ADT/MapVector.h (original)
> +++ llvm/trunk/include/llvm/ADT/MapVector.h Tue Jul 15 13:32:30 2014
> @@ -125,12 +125,26 @@ public:
>    }
>
>    /// \brief Remove the element given by Iterator.
> +  ///
>    /// Returns an iterator to the element following the one which was
> removed,
>    /// which may be end().
> +  ///
> +  /// \note This is a deceivingly expensive operation (linear time).  It's
> +  /// usually better to use \a remove_if() if possible.
>    typename VectorType::iterator erase(typename VectorType::iterator
> Iterator) {
> -    typename MapType::iterator MapIterator = Map.find(Iterator->first);
> -    Map.erase(MapIterator);
> -    return Vector.erase(Iterator);
> +    Map.erase(Iterator->first);
> +    auto Next = Vector.erase(Iterator);
> +    if (Next == Vector.end())
> +      return Next;
> +
> +    // Update indices in the map.
> +    size_t Index = Next - Vector.begin();
> +    for (auto &I : Map) {
> +      assert(I.second != Index && "Index was already erased!");
> +      if (I.second > Index)
> +        --I.second;
> +    }
> +    return Next;
>    }
>  };
>
>
> Modified: llvm/trunk/unittests/ADT/MapVectorTest.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/ADT/MapVectorTest.cpp?rev=213084&r1=213083&r2=213084&view=diff
>
> ==============================================================================
> --- llvm/trunk/unittests/ADT/MapVectorTest.cpp (original)
> +++ llvm/trunk/unittests/ADT/MapVectorTest.cpp Tue Jul 15 13:32:30 2014
> @@ -53,3 +53,18 @@ TEST(MapVectorTest, insert_pop) {
>    EXPECT_EQ(MV[1], 2);
>    EXPECT_EQ(MV[4], 7);
>  }
> +
> +TEST(MapVectorTest, erase) {
> +  MapVector<int, int> MV;
> +
> +  MV.insert(std::make_pair(1, 2));
> +  MV.insert(std::make_pair(3, 4));
> +  MV.insert(std::make_pair(5, 6));
> +  ASSERT_EQ(MV.size(), 3u);
> +
> +  MV.erase(MV.find(1));
> +  ASSERT_EQ(MV.size(), 2u);
> +  ASSERT_EQ(MV.find(1), MV.end());
> +  ASSERT_EQ(MV[3], 4);
> +  ASSERT_EQ(MV[5], 6);
> +}
>
>
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