Re: [PATCH 1/4] rs6000: Make all 128 bit scalar FP modes have 128 bit precision [PR112993]

[Richard Biener <richard.guenther@gmail.com>]

On Thu, May 9, 2024 at 9:12 PM Joseph Myers <josmyers@redhat.com> wrote:
>
> On Wed, 8 May 2024, Kewen.Lin wrote:
>
> > to widen IFmode to TFmode.  To make build_common_tree_nodes
> > be able to find the correct mode for long double type node,
> > it introduces one hook mode_for_longdouble to offer target
> > a way to specify the mode used for long double type node.
>
> I don't really like layering a hook on top of the old target macro as a
> way to address a deficiency in the design of that target macro (floating
> types should have their mode, not a poorly defined precision value,
> specified directly by the target).

Seconded.

> A better hook design might be something like mode_for_floating_type (enum
> tree_index), where the argument is TI_FLOAT_TYPE, TI_DOUBLE_TYPE or
> TI_LONG_DOUBLE_TYPE, replacing all definitions and uses of
> FLOAT_TYPE_SIZE, DOUBLE_TYPE_SIZE and LONG_DOUBLE_TYPE_SIZE with the
> single new hook and appropriate definitions for each target (with a
> default definition that uses SFmode for float and DFmode for double and
> long double, which would be suitable for many targets).

In fact replacing all of X_TYPE_SIZE with a single hook might be worthwhile
though this removes the "convenient" defaulting, requiring each target to
enumerate all standard C ABI type modes.  But that might be also a good thing.

The most pragmatic solution would be to do
s/LONG_DOUBLE_TYPE_SIZE/LONG_DOUBLE_TYPE_MODE/

Richard.

> --
> Joseph S. Myers
> josmyers@redhat.com
>