Re: [PATCH][sched-deps] Remove needless check for modified_in_p when trying to fuse two non-conditional jump insns

[Jeff Law <law at redhat dot com>]

On 11/13/14 07:09, Kyrill Tkachov wrote:

> I've updated the documentation for the hook.
> The testcase I was looking at involves fusing the AArch64 adrp+add
> instructions and depends on the backend implementation of the matching
> code, under review currently at
> https://gcc.gnu.org/ml/gcc-patches/2014-11/msg01263.html.
>
> I'm attaching a reduced testcase that generates an adrp and an add and
> due to the restriction addressed in this patch it doesn't call the
> backend hook for a pair of adrp and add instructions, causing them to be
> scheduled apart.
> I don't think it's a good candidate for the testsuite though because
> it's not easy to scan for consequent assembly instructions from Dejagnu
> and the instruction pair may end up scheduled together for some tuning
> parameters even though the macro fusion hook does not trigger for them
> as it should.
It's painful, but certainly possible to check for consecutive assembly 
instructions.  You just have to match the first instruction, its 
operands, a newline, then the 2nd instruction & operands.  The 
difficulty is in getting all the escape sequences right!

There are some examples of this.  For example mips/umips-branch-1.c

/* { dg-final { scan-assembler "\tjr?\t\\\$31\n\tmove\t\\\$2,\\\$0" } } */


Which looks for a jr instruction, some operands, then a move instruction 
on the next line.

As for instability, that's an inherent problem in some of this kind of 
stuff.  Just run it for the target you care about, possibly giving 
explicit tuning parameters that are known to make it trigger.

OK with a testcase.

jeff