This is the mail archive of the
gcc-bugs@gcc.gnu.org
mailing list for the GCC project.
Re: target/9832: ARM: Arithmetic and move could be combined using liveness information
- From: rearnsha at gcc dot gnu dot org
- To: gcc-bugs at gcc dot gnu dot org, gcc-prs at gcc dot gnu dot org, lac at rgai dot hu, nobody at gcc dot gnu dot org, rearnsha at gcc dot gnu dot org
- Date: 3 Mar 2003 14:14:27 -0000
- Subject: Re: target/9832: ARM: Arithmetic and move could be combined using liveness information
- Reply-to: rearnsha at gcc dot gnu dot org, gcc-bugs at gcc dot gnu dot org, gcc-prs at gcc dot gnu dot org, lac at rgai dot hu, nobody at gcc dot gnu dot org, rearnsha at gcc dot gnu dot org, gcc-gnats at gcc dot gnu dot org
Synopsis: ARM: Arithmetic and move could be combined using liveness information
Responsible-Changed-From-To: unassigned->rearnsha
Responsible-Changed-By: rearnsha
Responsible-Changed-When: Mon Mar 3 14:14:27 2003
Responsible-Changed-Why:
.
State-Changed-From-To: open->closed
State-Changed-By: rearnsha
State-Changed-When: Mon Mar 3 14:14:27 2003
State-Changed-Why:
The analysis for the reasons behind this are mistaken. GCC does get the liveness correct, but combine prevented from doing the combine into a hard register. The current register allocator fails to spot that the move can be eliminated and thus generates sub-optimal code. Compiling the same code with -fnew-ra shows that the new register allocator does a much better job in this area and eliminates the redundant move.
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9832