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author | Piotr Trojanek <trojanek@adacore.com> | 2022-10-18 09:33:38 +0200 |
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committer | Marc Poulhiès <poulhies@adacore.com> | 2022-11-07 09:36:36 +0100 |
commit | bcb3f09ec6cb9b2c6e58243d05b5a0fc33e909f1 (patch) | |
tree | 4df5daefb657713802fe88277389dedcf84e9a63 /gcc | |
parent | dc3208e698b2f424d892d3c9e5d5562ccde9e4cf (diff) | |
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ada: Tune hash function for cross-reference entries
Tune the hash function that combines entity identifiers with source
locations of where those entities are referenced. Previously the source
location was multiplied by 2 ** 7 (i.e. shifted left by 7 bits), then
added to the entity identifier, and finally divided modulo 2 ** 16 (i.e.
masked to only use the lowest 16 bits). This hash routine caused
collisions that could make some tests up to twice slower.
With a large entity number the source location was only contributing few
bits to the hash value. This large entity number might correspond to
entity like Ada.Characters.Latin_1.NUL that occurs thousands of times in
generated code.
gcc/ada/
* lib-xref.adb (Hash): Tune hash function.
Diffstat (limited to 'gcc')
-rw-r--r-- | gcc/ada/lib-xref.adb | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/gcc/ada/lib-xref.adb b/gcc/ada/lib-xref.adb index 043444c..5a1538e 100644 --- a/gcc/ada/lib-xref.adb +++ b/gcc/ada/lib-xref.adb @@ -1271,10 +1271,10 @@ package body Lib.Xref is XE : Xref_Entry renames Xrefs.Table (F); type M is mod 2**32; - H : constant M := M (XE.Key.Ent) + 2 ** 7 * M (abs XE.Key.Loc); + H : constant M := 3 * M (XE.Key.Ent) + 5 * M (abs XE.Key.Loc); -- It would be more natural to write: -- - -- H : constant M := M'Mod (XE.Key.Ent) + 2**7 * M'Mod (XE.Key.Loc); + -- H : constant M := 3 * M'Mod (XE.Key.Ent) + 5 * M'Mod (XE.Key.Loc); -- -- But we can't use M'Mod, because it prevents bootstrapping with older -- compilers. Loc can be negative, so we do "abs" before converting. |