Hi, Gr.Steven Very thanks for your replyment.
Induction variables are variables whose successive values form an arithmetic progression over a loop. Induction variables are often divided into bivs (basic induction variables), which are explicitly modified by the same constant amount during each iteration of a loop, and gives (general induction variables), which may be modified or computed by a linear-function of a basic induction variable. There are three important transformations that apply to them: strength reduction, induction-variable removal, and linear-function test replacement. For example, we can do strength reduction of address givs which are usually used for address calculation of array elements. On platforms with post-increment load and store instructions, this will make chance to combine a load/store with the following address calculation instruction. Also the induction variable splitting is an effective optimization during loop unrolling. The new loop optimizer only support a limited gives analysis (ref. loop-iv.c), and has not yet implemented giv splitting (ref. ¡®loop-unroll.c¡¯, ¡®analyze_iv_to_split_insn¡¯, and comments in this function, ¡°For now we just split the basic induction variables. Later this may be extended for example by selecting also addresses of memory references.¡±) I test 171.swim on IA64 system with 1GHz itanium2 CPU. After implemented or improved/adjusted several compile optimizations, such as Fortran alias analysis (very simple one), loop unrolling (the old one), loop arrays pre-fetching, and giv optimizations, it costs just 9.1s (28s for GCC-4.0.0) to execute the train mode of 171.swim. But, apply those changes on current GCC- 4.0.0 (the old loop unroller was removed), it costs 13.4 to execute this benchmark program, and I found that giv optimizations are the major factor of such performance degradation. Giv optimizations are just features which not implemented yet in the new loop unroller, so I think put it in bugzilla is not appropriate. Steven Bosscher <[EMAIL PROTECTED]>: > On Feb 28, 2005 02:35 PM, Canqun Yang <[EMAIL PROTECTED]> wrote: > > > Hi, all > > > > The new loop unroller causes performance degradation > > due to the unimplemented giv (general induction > > variable) optimizations. > > > > When will it be implemented? > > Will you be more specific so we can have a clue what you are > talking about? Filing bugs in bugzilla showing the problem > would help. > > Gr. > Steven > > Canqun Yang Creative Compiler Research Group. National University of Defense Technology, China.
