------- Comment #24 from dje at gcc dot gnu dot org 2006-01-03 15:50 ------- Comment #21 mentions three divisions for the optimization to be more profitable, but that information is lost by the time GCC reaches the expanders. Minimally, it would be helpful to know that the reciprocal optimization found more than three divides.
If the backend knew that it were calculating a reciprocal instead of 1./x division and that the reciprocal only occurs when more than two divides are present, it could produce better code. For both PowerPC and IA-64, it would be helpful to have RECIP_EXPR and the pair that completes division because both archtectures could then explicitly use their reciprocal instructions and fully schedule the Newton-Raphson or power-series expansion for the closure instead of generating the 1./x reciprocal as a full divide and the lower accuracy, isolated numerator multiplication separately. If the backends had more complete information, the reciprocal optimization could be extended beyond -ffast-math for some targets. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24123
