[rtl-optimization] Improve Data Prefetch for IA-64

[Canqun Yang]

Hi, all

Currently, GCC just ignores all data prefetches within 
loop when the number of prefetches exceeds 
SIMULTANEOUS_PREFETCHES. It isn't advisable. 

Also, macros defined in ia64.h for data prefetching 
are too small.

This patch modified the data prefetch algorithm 
defined in loop.c and redefines some macros in ia64.h 
accordingly. The test shows 2.5 percent perfomance 
improvements is gained for SPEC CFP2000 benchmarks on 
IA-64. If the new loop unroller was perfectly (just 
like the old one which was removed) implemented, much 
more performance improvements would be gained.

Canqun Yang
Creative Compiler Research Group.
National University of Defense Technology, China.
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