arm.md: Use the revsh and rev16 instructions for BSWAP:HI RTL in armv6 and up

This patch teaches the arm target about the rev16 and revsh
instructions which can
efficiently execute the recently added __builtin_bswap16() function
(BSWAP:HI in RTL)
These instructions are available in thumb and arm modes on armv6
architecture and up.

Before this patch,

short swaps16(short x) {
  return __builtin_bswap16(x);
}

unsigned short swapu16(unsigned short x) {
  return __builtin_bswap16(x);
}

$ gcc -S -dp -O2 -marm -march=armv6 test_bswap16.c
outputs:

swaps16:
        uxth    r3, r0  @ 8     *arm_zero_extendhisi2_v6/1      [length = 4]
        mov     r3, r3, lsr #8  @ 9     *arm_shiftsi3   [length = 4]
        orr     r0, r3, r0, asl #8      @ 12    *arith_shiftsi/1
 [length = 4]
        sxth    r0, r0  @ 19    *arm_extendhisi2_v6/1   [length = 4]
        bx      lr      @ 29    *arm_return     [length = 12]
swapu16:
        mov     r3, r0, lsr #8  @ 7     *arm_shiftsi3   [length = 4]
        orr     r0, r3, r0, asl #8      @ 10    *arith_shiftsi/1
 [length = 4]
        uxth    r0, r0  @ 16    *arm_zero_extendhisi2_v6/1      [length = 4]
        bx      lr      @ 26    *arm_return     [length = 12]


After this patch it produces:

swaps16:
        revsh   r0, r0  @ 13    *arm_revsh      [length = 4]
        bx      lr      @ 23    *arm_return     [length = 12]
swapu16:
        rev16   r0, r0  @ 6     *arm_rev16      [length = 4]
        uxth    r0, r0  @ 12    *arm_zero_extendhisi2_v6/1      [length = 4]
        bx      lr      @ 22    *arm_return     [length = 12]

Similar improvements are seen for -mthumb -march=armv6 and -mthumb
-march=armv6t2

--- ChangeLog ---
2012-04-16  Louis Kruger  <louisk@gmail.com>

        * arm.md: Use the revsh and rev16 instructions for BSWAP:HI
RTL in armv6 and up

---
 gcc/config/arm/arm.md |   41 +++++++++++++++++++++++++++++++++++++++++
 1 files changed, 41 insertions(+), 0 deletions(-)

On 16 April 2012 20:35, Louis Kruger <louisk@gmail.com> wrote:
> This patch teaches the arm target about the rev16 and revsh
> instructions which can
> efficiently execute the recently added __builtin_bswap16() function
> (BSWAP:HI in RTL)
> These instructions are available in thumb and arm modes on armv6
> architecture and up

Thank you for your patch but before taking this further , I have to
ask if  you have a valid copyright assignment on file with the FSF .I
would like to also see some testcases for this feature added to the
regression testsuite in gcc.target/arm.


regards,
Ramana

On 19.04.2012 09:05, Ramana Radhakrishnan wrote:
> On 16 April 2012 20:35, Louis Kruger <louisk@gmail.com> wrote:
>> This patch teaches the arm target about the rev16 and revsh
>> instructions which can
>> efficiently execute the recently added __builtin_bswap16() function
>> (BSWAP:HI in RTL)
>> These instructions are available in thumb and arm modes on armv6
>> architecture and up
> Thank you for your patch but before taking this further , I have to
> ask if  you have a valid copyright assignment on file with the FSF .I
> would like to also see some testcases for this feature added to the
> regression testsuite in gcc.target/arm.
>
>
> regards,
> Ramana
>

Louis,

Did you have time to sign a valid copyright assignment with FSF since you original patch?

If yes, do you plan to re-submit a patch taking Ramana's comments into account?

If no, do you mind if I propose a patch myself (maybe based on yours) ?

Thanks,

Christophe.