Hi all,
Currently on arm we miss some opportunities to generate the cmn instruction
(cmn r1, r2 ~ r1 + r2 == 0)
For example, for code:
int foo (int x, int y)
{
if (x + y == 0)
return 25;
else
return 5;
}
we generate
add r0, r0, r1
cmp r0, #0
movne r0, #5
moveq r0, #25
This could be improved. During investigation I noticed that combine tries to
transform x + y == 0 into x == -y, in RTL form: (eq (x) (neg y)) which is not
the canonical form and therefore doesn't get matched by a pattern we have that
would have produced a cmn instruction. Adding a re-canonicalization step in
simplify_comparison fixes that and allows us to match the correct patterns.
A new splitter is also added to arm that will allow us to produce forms
appropriate for cmn when doing comparisons other than == in the case given
above.
Bootstrapped on arm-linux-gnueabihf and x86_64-linux-gnu. Regtested on
arm-none-eabi on qemu.
Ok for trunk?
2013-07-25 Kyrylo Tkachov <kyrylo.tkachov@arm.com>
Richard Earnshaw <richard.earnshaw@arm.com>
* combine.c (simplify_comparison): Re-canonicalize operands
where appropriate.