Hi!

This patch generates LDRD instead of POP in epilogue for A15 ARM mode.

For optimize_size, original epilogue is generated for A15.
The work involves defining new functions, predicates and patterns.

In this patch we keep on accumulating non-consecutive registers till
register-pair to be popped is found. Then, first POP all the accumulated
registers, followed by LDRD with post-stack update for register-pair. We
repeat this until all the registers in register-list are POPPed.

The patch is tested with check-gcc, check-gdb and bootstrap with no
regression.
 
Changelog entry for Patch to emit LDRD for ARM epilogue in A15:

2011-10-11  Sameera Deshpande
<sameera.deshpande@arm.com>                                             
                                                                           
        * config/arm/arm.c (arm_emit_ldrd_pop): New static function.  
          (arm_expand_epilogue): Update. 
        * config/arm/ldmstm.md (arm_ldrd_base): New pattern.
          (arm_ldr_with_update): Likewise. 
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