Re: recent troubles with float vectors & bitwise ops

[Ian Lance Taylor <iant at google dot com>]

Chris Lattner <clattner@apple.com> writes:

> On Aug 24, 2007, at 8:02 AM, Ian Lance Taylor wrote:
> > Permitting this extension continues the preexisting behaviour, and it
> > helps programmers and helps existing code.  Who does it hurt to permit
> > this extension?  Who does it help to forbid this extension?
> 
> Aren't builtins the designated way to access processor-specific
> features like this?  Why does there have to be C operators for
> obscure features like this?

A fair question, but we've already decided to support vector + vector
and such operations, and we've decided that that is one valid way to
generate vector instructions.  That decision may itself have been a
mistake.  But once we accept that decision, then, given that we know
that the processor supports bitwise-or on floating point values, using
a instruction different from that for bitwise-or on integer values,
then it is fair to ask why we don't support vector | vector for
floating point vectors.

> Wouldn't it be better to fix the code generator to do the right thing
> regardless of how the user presents it?  There is a lot of code that
> uses casts (including the builtin implementations themselves) - it
> seems worthwhile to generate instructions for the right domain for
> this code as well.

I completely agree.

Ian