|
83 | 83 | -- [Note: Using INLINABLE] |
84 | 84 | -- ~~~~~~~~~~~~~~~~~~~~~~~ |
85 | 85 | -- It is crucial to the performance that the functions specialize on the Ord |
86 | | --- type when possible. GHC 7.0 and higher does this by itself when it sees th |
| 86 | +-- type when possible. GHC 7.0 and higher does this by itself when it sees the |
87 | 87 | -- unfolding of a function -- that is why all public functions are marked |
88 | 88 | -- INLINABLE (that exposes the unfolding). |
89 | 89 |
|
|
116 | 116 | -- floats out of its enclosing function and then it heap-allocates the |
117 | 117 | -- dictionary and the argument. Maybe it floats out too late and strictness |
118 | 118 | -- analyzer cannot see that these could be passed on stack. |
119 | | --- |
| 119 | + |
120 | 120 |
|
121 | 121 | -- [Note: Order of constructors] |
122 | 122 | -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
127 | 127 | -- On GHC 7.0, reordering constructors from Tip | Bin to Bin | Tip |
128 | 128 | -- improves the benchmark by up to 10% on x86. |
129 | 129 |
|
| 130 | + |
| 131 | +-- [Note: Matching on Leafy Nodes] |
| 132 | +-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| 133 | +-- In a balanced tree, at least two-thirds of Tip constructors are siblings |
| 134 | +-- of another Tip constructor. The parents of these cases can be quickly |
| 135 | +-- identified as the size value packed into their Bin constructors will equal |
| 136 | +-- 1. By specializing recursive functions which visit the whole tree to |
| 137 | +-- recognize this scenario, we can elide unnecessary function calls that would |
| 138 | +-- go on to match these Tip constructors but otherwise perform no useful work. |
| 139 | +-- This optimization can lead to performance improvements of approximately |
| 140 | +-- 30% to 35% for foldMap and foldl', and around 20% for mapMaybe. |
| 141 | +-- |
| 142 | +-- Alternatives, like matching on the Tip constructors directly, or also |
| 143 | +-- trying to optimise cases where only one side a Tip are slower in practice. |
| 144 | + |
| 145 | + |
130 | 146 | module Data.Map.Internal ( |
131 | 147 | -- * Map type |
132 | 148 | Map(..) -- instance Eq,Show,Read |
|
0 commit comments