[Issue 16513] Speed up TemplateInstance.findExistingInstance, hash by mangling

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=16513

Martin Nowak <code at dawg.eu> changed:

           What    |Removed                     |Added
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                 CC|                            |gooberman at gmail.com,
                   |                            |uplink.coder at googlemail.com

--- Comment #1 from Martin Nowak <code at dawg.eu> ---
It's the horrible hash that is causing the performance issue.
Arguments as widely different than

  genericIndexOf!(CPPMethods, ushort, int, uint, long, ulong)
  genericIndexOf!(VTable, ushort, int, uint, long, ulong)

produce the same hash.

>From the 88.3K lookups, 7900 have the hash 1 (one).

The test code that triggered the issue contains 1K instances of

  VariableDescriptor!(tonsofsimulatedobjects, SimulatedEntity,
"Simulated_Object_1063")
  VariableDescriptor!(tonsofsimulatedobjects, SimulatedEntity,
"Simulated_Object_1064")

and lots of instances like

  IsVariable!(Simulated_Object_963)
  IsMemberVariable!(Simulated_Object_973)
  isSomeFunction!(Simulated_Object_571)
  IsVariable!(Simulated_Object_964)
  IsMemberVariable!(Simulated_Object_974)
  isSomeFunction!(Simulated_Object_572)
  IsVariable!(Simulated_Object_966)
  IsMemberVariable!(Simulated_Object_975)
  isSomeFunction!(Simulated_Object_573)

all producing the same hash.
With such a crappy hash the behavior degrades back to the old linear search.

I'll try to replace this with the mangling suffix (.getIdent) instead which
should be both simpler and effective, given that all mangling bugs are fixed.

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