RE: libstdc++/5625: exception unwinding creates invalid pointer o n mips

[Ed Maste <emaste@SANDVINE.com>]

The following reply was made to PR libstdc++/5625; it has been noted by GNATS.

From: Ed Maste <emaste@SANDVINE.com>
To: "'echristo@gcc.gnu.org'" <echristo@gcc.gnu.org>, 
	"'echristo@redhat.com'" <echristo@redhat.com>, Ed Maste
	 <emaste@SANDVINE.com>, "'gcc-bugs@gcc.gnu.org'" <gcc-bugs@gcc.gnu.org>, 
	"'gcc-prs@gcc.gnu.org'" <gcc-prs@gcc.gnu.org>, "'gcc-gnats@gcc.gnu.org'"
	 <gcc-gnats@gcc.gnu.org>
Cc:  
Subject: RE: libstdc++/5625: exception unwinding creates invalid pointer o
	n mips
Date: Tue, 23 Apr 2002 15:35:33 -0400

 Yes, the MIPS documentation states that the destination register 
 gets the sign-extended result ("GPR[rt]<-sign_extend(temp31..0)").
 
 However, note the ADDIU instruction Restrictions section:
 
      Restrictions:
      If GPR rs does not contain a sign-extended 
      32-bit value (bits 63..31 equal), then the 
      result of the operation is UNPREDICTABLE.
 
 And then, on page 2:
 
      1.2.1 UNPREDICTABLE
      UNPREDICTABLE results may vary from processor 
      implementation to implementation, instruction 
      to instruction, or as a function of time on the 
      same implementation or instruction. Software can 
      never depend on results that are UNPREDICTABLE. 
      UNPREDICTABLE operations may cause a result to 
      be generated or not. If a result is generated,
      it is UNPREDICTABLE. UNPREDICTABLE operations 
      may cause arbitrary exceptions.
 
 -ed
 
 
 http://www.mips.com/publications/documentation/MD00087-2B-MIPS64BIS-AFP-00.9
 5.pdf
 
 (no comma attached to the end of the URL this time!)