Zdenek Dvorak wrote: > Hello, > > during expansion of expressions, gimplification creates a lot of temporary > variables. VAR_DECLs are fairly large (88 bytes on i686), and > additionally an annotation (44 bytes on i686) are allocated for each of > them (some of them even get names, for additional ~50 bytes of memory > each). This is quite wasteful.
Indeed; this is something I've been hoping we could fix for some time. > Basic observation is that these temporaries have exactly one definition. > It is therefore possible to generate directly SSA_NAMEs for them, > setting SSA_NAME_VAR to NULL (and be careful to never rewrite them out > of ssa). Theoretically, it should need only a few changes to gimplification, > into- and out-of-ssa, and expand, and everything should work. Unfortunately, > lot of SSA passes looks on SSA_NAME_VAR. This seems wrong to me, but > changing all the places would be very hard. > > However, if we instead put a really minimal DECL node (we allocate only > one per type, and consisting just of struct tree_common -- 16 bytes) as > a SSA_NAME_VAR, things are much easier to get working. I think we should do the complete patch. I know it's going to be tedious to fix the uses of SSA_NAME_VAR, but I think that would be much cleaner, and will also avoid problems where we have a DECL (GVAR_DECL) that is missing fields that other parts of the compiler might expect a DECL to have. -- Mark Mitchell CodeSourcery [EMAIL PROTECTED] (650) 331-3385 x713
