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Re: g77 performance on ALPHA
- To: martin.kahlert@provi.de
- Subject: Re: g77 performance on ALPHA
- From: Richard Henderson <rth@cygnus.com>
- Date: Sat, 28 Aug 1999 11:44:10 -0700
- Cc: egcs@egcs.cygnus.com
- References: <199908281130.NAA00385@keksy.linux.provi.de>
On Sat, Aug 28, 1999 at 01:30:48PM +0200, martin.kahlert@provi.de wrote:
> So i tested with a small daxpy operation:
> SUBROUTINE DAXPY(N,ALPHA,X,I1,Y,I2)
> IMPLICIT NONE
> INTEGER*4 N,I,I1,I2
> REAL*8 ALPHA,X(N),Y(N)
>
> DO I=1, N
> Y(I)=Y(I)+ALPHA*X(I)
> ENDDO
> RETURN
> END
[...]
> The loop isn't unrolled with -funroll-loops, either.
Nope. We don't know how to efficiently unroll loops with
non-constant bounds. We don't try unless forced ...
> Using -funroll-all-loops, we get...
... at which point we generate the somewhat horid code you saw.
r~