[llvm-commits] [patch] Intruction Constraint DestReg!=SrcReg (for review)

[Chris Lattner]

On Jan 26, 2007, at 1:08 PM, Lauro Ramos Venancio wrote:

> Hi Chris,
>
> In ARM v4/v5 specification, mul %r0, %r0, %r1 (r0 = r0*r1) is invalid,
> but mul %r0, %r1, %r0 is valid. With early-clobber constraint, ARM
> backend wouldn't emit the the mul %r0, %r1, %r0. We need a constraint
> only for the first source register.

Yep, makes sense.  It would be nice if the mechanism you guys invent  
can *also* handle early-clobber, even if it's not a one-to-one  
mapping.  For example, use of early clobber could translate into a  
bunch of != constraints.

-Chris