On Mon, Nov 10, 2014 at 05:27:50PM -0500, David Malcolm wrote:
> On Sat, 2014-11-08 at 14:56 +0100, Jakub Jelinek wrote:
> > On Sat, Nov 08, 2014 at 01:07:28PM +0100, Richard Biener wrote:
> > > To be constructive here - the above case is from within a
> > > GIMPLE_ASSIGN case label
> > > and thus I'd have expected
> > >
> > > case GIMPLE_ASSIGN:
> > > {
> > > gassign *a1 = as_a <gassign *> (s1);
> > > gassign *a2 = as_a <gassign *> (s2);
> > > lhs1 = gimple_assign_lhs (a1);
> > > lhs2 = gimple_assign_lhs (a2);
> > > if (TREE_CODE (lhs1) != SSA_NAME
> > > && TREE_CODE (lhs2) != SSA_NAME)
> > > return (operand_equal_p (lhs1, lhs2, 0)
> > > && gimple_operand_equal_value_p (gimple_assign_rhs1 (a1),
> > > gimple_assign_rhs1
> > > (a2)));
> > > else if (TREE_CODE (lhs1) == SSA_NAME
> > > && TREE_CODE (lhs2) == SSA_NAME)
> > > return vn_valueize (lhs1) == vn_valueize (lhs2);
> > > return false;
> > > }
> > >
> > > instead. That's the kind of changes I have expected and have approved of.
> >
> > But even that looks like just adding extra work for all developers, with no
> > gain. You only have to add extra code and extra temporaries, in switches
> > typically also have to add {} because of the temporaries and thus extra
> > indentation level, and it doesn't simplify anything in the code.
>
> The branch attempts to use the C++ typesystem to capture information
> about the kinds of gimple statement we expect, both:
> (A) so that the compiler can detect type errors, and
> (B) as a comprehension aid to the human reader of the code
>
> The ideal here is when function params and struct field can be
> strengthened from "gimple" to a subclass ptr. This captures the
> knowledge that every use of a function or within a struct has a given
> gimple code.
I just don't like all the as_a/is_a stuff enforced everywhere,
it means more typing, more temporaries, more indentation.
So, as I view it, instead of the checks being done cheaply (yes, I think
the gimple checking as we have right now is very cheap) under the
hood by the accessors (gimple_assign_{lhs,rhs1} etc.), those changes
put the burden on the developers, who has to check that manually through
the as_a/is_a stuff everywhere, more typing and uglier syntax.
I just don't see that as a step forward, instead a huge step backwards.
But perhaps I'm alone with this.
Can you e.g. compare the size of - lines in your patchset combined, and
size of + lines in your patchset? As in, if your changes lead to less
typing or more.
Jakub
