[PATCH] Defer address legitimization for expanded ARRAY_REF, COMPONENT_REF, etc. til the final address is computed

[Yufeng Zhang <Yufeng dot Zhang at arm dot com>]

Hi,

Currently the address legitimization (by calling 
memory_address_addr_space) is carried out twice during the RTL expansion 
of ARRAY_REF, COMPONENT_REF, etc. when their OFFSET is not NULL.  It is 
done once for the BASE and once for the summed address in 
offset_address. This may cause part, if not all, of the generated BASE 
RTL to be forced into reg(s), preventing the RTL generator from carrying 
out effective re-association across BASE and OFFSET (via 
simplify_gen_binary).

For example, given the following test case:

typedef int arr_2[20][20];
void foo (arr_2 a2, int i, int j)
{
  a2[i+10][j] = 1;
}

the RTL code for the BASE (i.e. a2[i+10]) on arm (-mcpu=cortex-a15, 
-mthumb) is

* before the legitimization of BASE:

(plus:SI (plus:SI (mult:SI (reg/v:SI 115 [ i ])
            (const_int 80 [0x50]))
        (reg/v/f:SI 114 [ a2 ]))
    (const_int 800 [0x320]))
(reg/f:SI 122)

* after the legitimization of BASE:

(reg/f:SI 122)

"Thanks to" the initial legitimization, the RTL for the final address is 
turned into:

(plus:SI (mult:SI (reg/v:SI 116 [ j ])
        (const_int 4 [0x4]))
    (reg/f:SI 122))

while with the legitimization deferred, the RTL for the final address 
could be:

(plus:SI (plus:SI (plus:SI (mult:SI (reg/v:SI 115 [ i ])
                (const_int 80 [0x50]))
            (mult:SI (reg/v:SI 116 [ j ])
                (const_int 4 [0x4])))
        (reg/v/f:SI 114 [ a2 ]))
    (const_int 800 [0x320]))

which has more complete info in the RTL and is much more canonicalized; 
later on it could open up more opportunities for CSE.

The effect of this duplicated legitimization effort varies across 
different targets, as it is strongly related to the available addressing 
modes on a target.  On RISC machines where in general there are fewer 
addressing modes (which are in general less complicated as well), the 
RTL code quality can be affected more adversely.

The patch passes bootstrapping on arm and x86_64 and regtest on 
arm-none-eabi, aarch64-none-elf and x86_64.  There is no regression in 
spec2000 on arm or x86_64.

OK for the mainline?

Thanks,
Yufeng


gcc/

        * cfgexpand.c (expand_call_stmt): Update the call to 
expand_expr_real_1.
        * expr.c (expand_assignment): Add new local variable validate_p 
and set
        it; call expand_expr or expand_expr_nv depending on validate_p for
        to_rtx; call adjust_address_1 instead of adjust_address.
        (store_expr): Update the call to expand_expr_real.
        (expand_expr_real): Add new parameter 'validate_p'; update the 
call to
        expand_expr_real_1.
        (expand_expr_real_1): Add new parameter 'validate_p'; update 
the call
        to expand_expr_real; depending on validate_p, call
        memory_address_addr_space or convert_memory_address_addr_space;
        likewise for expand_expr or expand_expr_nv; call adjust_address_1
        instead of adjust_address.
        * expr.h (expand_expr_real): Update.
        (expand_expr_real_1): Update.
        (expand_expr): Update.
        (expand_expr_nv): New function.
        (expand_normal): Update.

Attachment: patch.txt
Description: Text document