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Re: About the is_gimple_min_invariant predicate


On 7/4/07, Richard Kenner <kenner@vlsi1.ultra.nyu.edu> wrote:
> Also, we need to update the GIMPLE grammar so that ARRAY_REF and
> ARRAY_RANGE_REF take the appropriate values:

A minor comment is that operand 2 of COMPONENT_REF needs the same handling.

Can you please, again,  explain why we even have this wasting space in
all the component_ref's?

tree.def simply says "  Operand 2, if present, is the value of
DECL_FIELD_OFFSET, measured
  in units of DECL_OFFSET_ALIGN / BITS_PER_UNIT."

It doesn't say why this can't be computed on the fly and have 1 bit
that says whether we need to use that value or not.
Assuming this is impossible to be computed on the fly for some reason,
it also doesn't explain why we are wasting space on every single
component_ref when only some incredibly small percentage have this
set, instead of just using 1 bit + a hash table of mapping component
ref -> this value.


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