Re: Propagation of "pointer" attribute on registers

[James E Wilson <wilson at specifixinc dot com>]

Pat Haugen wrote:
> Is there a reason REG_POINTER isn't propagated to the target register for
> rtl insns of the form "reg_x = regP_y + reg_z", where regP_y is a reg
> marked as REG_POINTER?

Probably historical oversight.

However, note that the hppa-hp-hpux port relies on the REG_POINTER 
settings being conservatively correct.  This is because it uses 
segmented addresses, and in a reg+reg address, it requires knowing which 
one is the pointer when emitting assembly language.  If REG_POINTER is 
set for things that aren't actually pointer values, then the 
hppa-hp-hpux port can break.  I'd think it would be safe to add the 
reg=reg+reg case here, but it should be checked.

The aliasing code could perhaps be using the newer REG_ATTRS field 
instead of REG_POINTER.  REG_EXPR didn't exist when alias.c was written, 
and may help here.  Or maybe not.  The REG_EXPR case in 
reg_scan_mark_refs is even more restrictive than the REG_POINTER code; 
it doesn't handle REG+CONST.
--
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com