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Date: Tue, 11 Jan 2011 13:30:00 -0000
Message-ID: <AANLkTik2wJirOgyQ+ophpOhH-hjSv3K3Xj4DPrPk545v@mail.gmail.com>
Subject: Plus Reload
From: Gidi Nave <gidi.nave.1@gmail.com>
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Hi,

I have a question regarding Plus reload situation I ran into in my
port (which was taken from branch 4.6):

I got the following insn:=A0 Set d1=A0 (plus r1 -96).
d1 and r1 are 2 registers from different classes.

The reload (which take place at: reload1.c , gen_reload(out =3D d1, in =3D
(plus r1 -96)) try 3 options:

1. switch the plus operands:
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 set d1 (plus -96 r1)

2. split into 2 insns - reload the const to d1 and then add r1:
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 set d1 -96
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 set d1=A0 (plus d1 r1)

3. split into 2 insns - copy r1 to d1 and then add the const:
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 set d1 r1
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 set d1=A0 (plus d1 -96)

GCC tries generating the 1st option - and fails since no valid pattern is f=
ound.
Then it tries generating the 2nd option and fails once again, since no
valid pattern is found.
Then it tries generating the 3rd option without constraint validity
check(emit_insn_if_valid_for_reload) like the first 2 attempts,
and creates a new insn which will later fail since it's not satisfying
it's constraints.

My question is: why is GCC certain that one of those 3 attempts must work?
In my case, all 3 resulted insns are not supported by the architecture.

Thanks,
Gidi.