On 06/08/2018 06:21 AM, Paul Koning wrote:
Interesting. The ChangeLog doesn't give any background. I suppose I should
plan to approximate the effect of this pattern with a define-peephole2 ?
The old RTL loop optimizer was replaced with a new RTL loop optimizer.
When the old one was written, m68k was a major target, and the dbra
optimization was written for it. When the new one was written, m68k was
not a major target, and this support was written differently. We now
have doloop_begin and doloop_end patterns that do almost the same thing,
and can be created by the loop-doloop.c code.
There is a section in the internals docs that talks about this.
https://gcc.gnu.org/onlinedocs/gccint/Looping-Patterns.html
The fact that we still have decrement_and_branch_until_zero references
in docs and target md files looks like a bug. The target md files
should use doloop patterns instead, and the doc references should be
dropped.
Jim
