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Set TARGET_OMIT_STRUCT_RETURN_REG to true 

The reason this caught my eye on aarch64 is because
the return value register (x0) is not identical to the register in which
the hidden parameter for AArch64 is set (x8). Thus setting this to true
seems to be quite reasonable and shaves off 100 odd mov x0, x8's from
cc1 in a bootstrap build.

I don't expect this to make a huge impact on performance but as they
say every little counts.  The AAPCS64 is quite explicit about not
requiring that the contents of x8 be kept live.

Bootstrapped and regression tested on aarch64.

Ok to apply ?

Ramana

gcc/
* config/aarch64/aarch64.c (TARGET_OMIT_STRUCT_RETURN_REG): Set to
true.

gcc/testsuite

* gcc.target/aarch64/struct_return.c: New test.

From-SVN: r236197
This commit is contained in:
Ramana Radhakrishnan 2016-05-13 09:23:28 +00:00 committed by Ramana Radhakrishnan
parent 44cb09ea6b
commit 43203dea1a
4 changed files with 43 additions and 0 deletions
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5
gcc/ChangeLog
View File

@ -1,3 +1,8 @@
2016-05-13 Ramana Radhakrishnan <ramana.radhakrishnan@arm.com>
* config/aarch64/aarch64.c (TARGET_OMIT_STRUCT_RETURN_REG): Set
to true.
2016-05-13 Rainer Orth <ro@CeBiTec.Uni-Bielefeld.DE>
PR target/71080

3
gcc/config/aarch64/aarch64.c
View File

@ -14232,6 +14232,9 @@ aarch64_optab_supported_p (int op, machine_mode, machine_mode,
#undef TARGET_OPTAB_SUPPORTED_P
#define TARGET_OPTAB_SUPPORTED_P aarch64_optab_supported_p
#undef TARGET_OMIT_STRUCT_RETURN_REG
#define TARGET_OMIT_STRUCT_RETURN_REG true
struct gcc_target targetm = TARGET_INITIALIZER;
#include "gt-aarch64.h"

4
gcc/testsuite/ChangeLog
View File

@ -1,3 +1,7 @@
2016-05-13 Ramana Radhakrishnan <ramana.radhakrishnan@arm.com>
* gcc.target/aarch64/struct_return.c: New test.
2016-05-12 Marek Polacek <polacek@redhat.com>
PR c/70756

31
gcc/testsuite/gcc.target/aarch64/struct_return.c Normal file
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@ -0,0 +1,31 @@
/* Test the absence of a spurious move from x8 to x0 for functions
return structures. */
/* { dg-do compile } */
/* { dg-options "-O2" } */
struct s
{
long x;
long y;
long z;
};
struct s __attribute__((noinline))
foo (long a, long d, long c)
{
struct s b;
b.x = a;
b.y = d;
b.z = c;
return b;
}
int
main (void)
{
struct s x;
x = foo ( 10, 20, 30);
return x.x + x.y + x.z;
}
/* { dg-final { scan-assembler-not "mov\tx0, x8" } } */