nop..in gcc-4.4.2. :: reason for requirement

[Ian Lance Taylor]

isha Kandaswamy <isha.kandaswamy@gmail.com> writes:

> When I was compiling gcc 4.4.2 for a certain machine description, I realized
> that it needed a nop pattern in the md. This was being called by cfglayout.c
> in the function fixup_reorder_chain. This call was not made in the previous
> version of gcc I was using namely gcc-4.3.1. My doubt is whay do we need the
> nop pattern in gcc-4.4.2 and not in gcc-4.3.1. I also have another doubt.
> What does the function copy_to_reg do? Why does it require a movsi pattern
> in the machine descriptions ?

I've Bcc'ed almost everybody.  Please don't send messages to a huge
group of people like this.  Please don't send messages to both
gcc@gcc.gnu.org and gcc-patches@gcc.gnu.org.  Thanks.

New versions of gcc impose new requirements on backends.  That's just
the way it works.  The gen_nop call in cfglayout.c is to improve
debuggability of code compiled with -O0, by giving debuggers a place
to set a breakpoint on an edge which otherwise contains no
instructions.

The copy_to_reg function copies a value into a register.  It requires
a movMM insn where MM is the mode of the value.  In general a gcc
backend must have a movMM insn for all supported modes.

Ian