On 11/02/2011 08:23 PM, DJ Delorie wrote: > GCC assumes the target has a multiply insn, but better code is > generated using shifts if it doesn't (vs a libcall). Found with the > rl78-elf port. > > * expr.c (expand_expr_real_2): Don't try to emit a MUL-based > expression if the target doesn't have a multiply pattern. Fall > back to shifts instead of using libgcc calls. > > Index: gcc/expr.c > =================================================================== > --- gcc/expr.c (revision 180758) > +++ gcc/expr.c (working copy) > @@ -8289,12 +8289,13 @@ expand_expr_real_2 (sepops ops, rtx targ > } > > /* Attempt to return something suitable for generating an > indexed address, for machines that support that. */ > > if (modifier == EXPAND_SUM && mode == ptr_mode > + && optab_handler (smul_optab, mode) != CODE_FOR_nothing
This is the wrong place for this. With EXPAND_SUM we're expecting to generate something that is applicable to addresses, and the addressing form is canonically (plus (mult x n) y). This does suggest, though, that something ought to be using expand_mult and not expand_simple_binop. It's not immediately obvious what that something is, since my first guess was force_operand and it *does* use expand_mult. r~
