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Re: [PATCH, i386]: Emit cld instruction when stringops are used
On Mon, Apr 28, 2008 at 01:38:28PM +0200, Uros Bizjak wrote:
> On Mon, Apr 28, 2008 at 1:16 PM, Joseph S. Myers
> <joseph@codesourcery.com> wrote:
>
> > > This patch adds back generation of cld instructions when stringops are
> > > used in the function. cld insn is emitted as unspec volatile at the
> > > end of function prologue. Currently, patched gcc emits cld when
> > > "-mcld" is added to compile flags.
> >
> > The discussion of this patch seems to have died down, and we were hoping
> > to get something like this into GCC 4.3.1.
> >
> > I think the conclusion was that the approach of this patch (emit cld in
> > the prologue if the compiler generates code caring about the direction
> > flag, but inline asms need their own cld if they care about the direction
> > flag) is the right one. There was less consensus on the need for a
> > configure option to turn this option on by default, but if there is one
> > then I think the right form is --enable-cld which turns it on by default
> > for 32-bit code only, if no explicit -mno-cld option was passed.
>
> IIRC, Jan proposed better patch, where cld was placed in optimal
> position via LCM.
I believe that idea rejected as it meant big amount of changes, which isn't
desirable on the branch.
Jakub