Convey spesh facts better in p6decontrv.
Convey spesh facts better in p6decontrv.

This allows spesh, when it knows (or has guarded on) the return type
already, to toss the return type checks entirely. This also boots out
the Nil checking and error handling basic blocks, shortening the
specialized bytecode by a couple of basic blocks, or approximately
12 instructions, which will in turn help bring more things under the
inline limit.

Gnouc/rakudo,usev6/rakudo,awwaiid/rakudo,salortiz/rakudo,labster/rakudo,salortiz/rakudo,lucasbuchala/rakudo,lucasbuchala/rakudo,rakudo/rakudo,sjn/rakudo,jonathanstowe/rakudo,usev6/rakudo,MasterDuke17/rakudo,jonathanstowe/rakudo,MasterDuke17/rakudo,jonathanstowe/rakudo,raydiak/rakudo,Gnouc/rakudo,rakudo/rakudo,MasterDuke17/rakudo,lucasbuchala/rakudo,nbrown/rakudo,tony-o/rakudo,nbrown/rakudo,Gnouc/rakudo,salortiz/rakudo,tony-o/rakudo,tbrowder/rakudo,tony-o/rakudo,softmoth/rakudo,tony-o/rakudo,salortiz/rakudo,awwaiid/rakudo,usev6/rakudo,raydiak/rakudo,sjn/rakudo,raydiak/rakudo,tbrowder/rakudo,labster/rakudo,softmoth/rakudo,nbrown/rakudo,tbrowder/rakudo,awwaiid/rakudo,tbrowder/rakudo,softmoth/rakudo,tbrowder/rakudo,softmoth/rakudo,lucasbuchala/rakudo,sjn/rakudo,lucasbuchala/rakudo,jonathanstowe/rakudo,Gnouc/rakudo,salortiz/rakudo,nbrown/rakudo,Gnouc/rakudo,rakudo/rakudo,MasterDuke17/rakudo,tony-o/rakudo,labster/rakudo,sjn/rakudo,raydiak/rakudo,nbrown/rakudo,MasterDuke17/rakudo,jonathanstowe/rakudo,sjn/rakudo,awwaiid/rakudo,rakudo/rakudo,labster/rakudo,usev6/rakudo,rakudo/rakudo,rakudo/rakudo,salortiz/rakudo,labster/rakudo,tbrowder/rakudo,usev6/rakudo,nbrown/rakudo,labster/rakudo,Gnouc/rakudo,tony-o/rakudo,MasterDuke17/rakudo,softmoth/rakudo,awwaiid/rakudo