Re: IA32: printing FP register variables

[Joern Rennecke <amylaar@cygnus.co.uk>]

> I'm not sure this is safe either.  Consider what happens at basic block
> boundaries to the regstack.   I believe variables location relative to 
> the bottom of the stack can change at a basic block boundary.

Huh?  Why that?  The FPU doesn't know about the control flow.
From law@cygnus.com Mon Jul 12 17:07:00 1999
From: Jeffrey A Law <law@cygnus.com>
To: Joern Rennecke <amylaar@cygnus.co.uk>
Cc: jimb@cygnus.com, egcs@egcs.cygnus.com, gdb@sourceware.cygnus.com
Subject: Re: IA32: printing FP register variables 
Date: Mon, 12 Jul 1999 17:07:00 -0000
Message-id: <9384.931824345@upchuck.cygnus.com>
References: <199907122349.AAA25740@phal.cygnus.co.uk>
X-SW-Source: 1999-q3/msg00057.html
Content-length: 766

  In message < 199907122349.AAA25740@phal.cygnus.co.uk >you write:
  > > I'm not sure this is safe either.  Consider what happens at basic block
  > > boundaries to the regstack.   I believe variables location relative to 
  > > the bottom of the stack can change at a basic block boundary.
  > 
  > Huh?  Why that?  The FPU doesn't know about the control flow.
Consider two threads of control, each with one variable on the FP stack.

At some point they merge.  One variable has to be on the bottom, the other
on the top.

regstack has to track this stuff and emit appropriate code at block boundaries
to move stuff around via copies.

It is also why I believe an LCM based copy propagation algorithm can be used
to improve the code generated by regstack.


jeff