Re: [RFC] Do pointer comparison first in operand_equal_p

[Roger Sayle <roger at eyesopen dot com>]

On Fri, 13 May 2005, Diego Novillo wrote:
> Jeff had some doubts about the approach.  Roger, what do you
> think?  Any reason why this would be unsafe in general?

Hi Diego,

The problem that I see with this is its interaction with the
OEP_CONST_ONLY and OEP_PURE_SAME flags.  When the tree-ssa branch
was merged into mainline, it brought along Jeff's changes to
operand_equal_p to allow the tree-optimizers to specify that they
only want constants considered equal iff OEP_CONST_ONLY was
specified.

See:
>> 2004-05-13  Diego Novillo  <dnovillo@redhat.com>
>>       Merge from tree-ssa-20020619-branch.


The side-effect is that this increases the critical path length of
operand_equal_p, which is heavily used.  Perhaps a better approach
would be to split up the two functionalities, into operand_equal_p
and constant_equal_p (and maybe pure_call_equal_p) such that each
implementation attempts to reuse as much as possible, but its
optimized for it's particular usage.

i.e. operand_equal_p could call constant_equal_p for constants,
allowing the pointer comparison to occur first in the former.


As written your patch may break stuff.

Roger
--