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Re: [PATCH][AArch64] Improve TARGET_LEGITIMIZE_ADDRESS_P hook


Hi Venkataramanan,

thanks for review.

On 01/08/14 11:59, Venkataramanan Kumar wrote:
Hi Jiong,

(Snip)
+  && (op0 == virtual_stack_vars_rtx
+      || op0 == frame_pointer_rtx
+      || op0 == arg_pointer_rtx)
(Snip)

The above check is means that these are the ways to access the frame.
is it possible to have stack_pointer_rtx has op0?

I think there is no necessary to add stack_pointer_rtx check here.

because normally all local variables will be addressed using virtual_stack_vars_rtx,
and then rebased to frame_pointer_rtx in instantiate_new_reg, and finally eliminated
to fp/sp during reload depending on whether frame pointer is needed. so

+  && (op0 == virtual_stack_vars_rtx
+      || op0 == frame_pointer_rtx

could actually catch almost all we want.

-- Jiong



On 1 August 2014 14:01, Jiong Wang <jiong.wang@arm.com> wrote:
currently, aarch64 LEGITIMIZE_ADDRESS_P hook will reject all "reg + offset"
address given
"offset" is beyond supported range.

while this may be too strict. we should honor the "strict_p" parameter in
the hook. before
reload, we accept all offset if it's a frame access, because the offset may
change during
later register elimination.

the early reject of "reg + offset" may cause extra registers created, and if
that register
live range is across function invoking then callee saved reg needed, thus
introduce extra
reg save/restore also.

give a simple example as:

int
test15 (void)
{
   unsigned char a[480];
   initialize_array (a, 480);

   if (a[0] == 0x10)
     return 1;

   return 0;
}

.S before the patch
(-O2 -fPIC)
===
test15:
         sub     sp, sp, #480
         mov     w1, 480
         stp     x29, x30, [sp, -32]!
         add     x29, sp, 0
         str     x19, [sp, 16]
         add     x19, x29, 32
         mov     x0, x19
         bl      initialize_array
         ldrb    w0, [x19]
         ldr     x19, [sp, 16]
         ldp     x29, x30, [sp], 32
         cmp     w0, 16
         cset    w0, eq
         add     sp, sp, 480
         ret

.S after the patch
===
test15:
         stp     x29, x30, [sp, -496]!
         mov     w1, 480
         add     x29, sp, 0
         add     x0, x29, 16
         bl      initialize_array
         ldrb    w0, [x29, 16]
         ldp     x29, x30, [sp], 496
         cmp     w0, 16
         cset    w0, eq
         ret

test done
=========
no regression on aarch64-none-elf bare metal.
bootstrap OK on aarch64.

OK for trunk?

thanks.

gcc/
   * config/aarch64/aarch64.c (aarch64_classify_address): Accept all offset
for frame access
   when strict_p is false.

gcc/testsuite
   * gcc.target/aarch64/legitimize_stack_var_before_reload_1.c: New testcase.



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