Nathan Froyd <froy...@codesourcery.com> writes: > Compiling anything that uses doubles on powerpc e500v2 produces awful > code due in part to lower-subregs (the register allocator doesn't help, > either, but that's a different story). Code that looks like: > > rY:DI = r<ARG>:DI > rX:DI = rY:DI > (subreg:DF rZ:DI 0) = rX:DI > > <ARG> is a hard register for argument passing; the code looks equally > awful inside of a function, too. The above gets lowered to: > > 1: r<Y>:SI = r<ARG>:SI > 2: r<Y+1>:SI = r<ARG+1>:SI > 3: (subreg:SI rX:DI 0) = r<Y>:SI > 4: (subreg:SI rX:DI 4) = r<Y+1>:SI > 5: (subreg:DF rZ:DI 0) = rX:DI > > which usually results in two stores and a load against the stack, rather > than a single-instruction dealing entirely in registers. I realize > e500v2 is not exactly a mainstream target, but perhaps a target hook is > appropriate here? I suppose checking costs might achieve the same > thing.
I doubt that a target hook is required to avoid this. Perhaps simple_move_operand should reject a mode changing subreg when the two modes are !MODE_TIEABLE_P. This code is sort of weird, though; why the conversion from DImode to DFmode? Ian
