> -----Original Message----- > From: gcc-patches-ow...@gcc.gnu.org [mailto:gcc-patches- > ow...@gcc.gnu.org] On Behalf Of Jiangning Liu > Sent: Wednesday, December 21, 2011 2:48 PM > To: 'Richard Henderson' > Cc: gcc-patches@gcc.gnu.org; 'Richard Guenther' > Subject: RE: [RFC] Use REG_EXPR in back-end (introduced by optimization > to conditional and/or in ARM back-end) > > > > -----Original Message----- > > From: Richard Henderson [mailto:r...@redhat.com] > > Sent: Tuesday, November 22, 2011 9:55 AM > > To: Jiangning Liu > > Cc: gcc-patches@gcc.gnu.org; 'Richard Guenther' > > Subject: Re: [RFC] Use REG_EXPR in back-end (introduced by > optimization > > to conditional and/or in ARM back-end) > > > > On 11/21/2011 05:31 PM, Jiangning Liu wrote: > > > My question is essentially is "May I really use REG_EXPR in back- > end > > code?" > > > like the patch I gave below? > > > > I suppose. > > > > Another alternative is to use BImode for booleans. Dunno how much of > > that > > you'd be able to gleen from mere rtl expansion or if you'd need > boolean > > decls to be expanded with BImode. > > Hi Richard, > > The output of expand pass requires the operands must meet the > requirement of > general_operand for binary operations, i.e. all RTX operations on top > level > must meet the hardware instruction requirement. Generally for a > hardware not > directly supporting a single bit logic operation, we can't generate BI > mode > rtx dest. > > So if I simply generate BImode for NE in expand pass, like "subreg:SI > (ne:BI > (reg:SI xxx) (const_int 0)))", there would be an assertion failure due > to > failing to find an appropriate instruction code to operate on a single > bit. > > This looks like a GCC design level issue. How would you suggest > generating a > legitimate rtx expression containing BImode? >
Can anybody give me useful suggestions on this issue? My question essentially is may I really use BImode to solve my original problem? Thanks, -Jiangning > Thanks, > -Jiangning > > > > > The later would probably need a target hook. I've often wondered how > > much > > ia64 would benefit from that too, being able to store bool variables > > directly > > in predicate registers. > > > > All of this almost certainly must wait until stage1 opens up again > > though... > > > > > > r~ > > > >
