On 05/17/2015 10:21 AM, Jon Beniston wrote:
Hi,
The gccint docs for pre_modify/post_modify say that the address modifier
must be one of three forms:
(plus:m x z), (minus:m x z), or (plus:m x i), where z is an index register
and i is a constant.
Why isn’t (plus:m x (mult:m z i)) supported, for architectures that support
scaling of the index register (E.g. ARM?)
Compiling:
int *f(int *p, int x, int z)
{
p[z] = x;
return p + z;
}
For ARM results in:
str r1, [r0, r2, asl #2]
add r0, r0, r2, asl #2
Rather than just:
str r1, [r0, r2, asl #2]!
Should this be improved by expanding what pre/post_modify supports, as
above, or perhaps a peephole optimisation?
I don't think it was really considered with we added pre/post_modify a
while back -- IIRC it was primarily driven by whatever port Michael
Hayes was working on at the time plus the capabilities of PPC and HPPA
at the time.
We'd certainly welcome patches to support scaling in the pre/post_modify
addressing modes.
jeff
