On Fri, 27 Feb 2009, Zdenek Dvorak wrote: > Hi, > > > > introducing new codes seems like a bad idea to me. There are many > > > places that do not care about the distinction between PLUS_EXPR and > > > PLUSV_EXPR, and handling both cases will complicate the code (see eg. > > > the problems caused by introducing POINTER_PLUS_EXPR vs PLUS_EXPR > > > distinction). Why not just use a flag to mark the operation as > > > non-overflowing? > > > > I obviously thought about this. The issue with using a flag is > > that there is no convenient place to stick it and that it makes > > the distinction between the two variants less visible. Consider > > the folding routines that take split trees for a start. > > > > IMHO using new tree-codes is much less complicated than carrying > > around flags. I did consider putting flags on the tree code > > itself, but that isn't going to make the changes easier either. > > OK, then what about this: introduce accessor functions like > > tree_code get_operation_semantics (tree_code) > -- returns PLUS_EXPR for PLUS_EXPR and PLUSNV_EXPR, etc. > bool get_operation_overflow (tree_code) > -- obvious > tree_code operation_code (tree_code, bool) > -- PLUS_EXPR, false -> PLUS_EXPR > -- PLUS_EXPR, true -> PLUSNV_EXPR > -- PLUSNV_EXPR, * -> abort > etc. > > (possibly with more clear names), and change the code to always > use them?
Yes. In playing with an initial patch I see the need for these kind of helpers. Sofar I tried to limit myself to PLUS_EXPR_P () covering both kinds, but that certainly is not enough. So I see the need for at least tree_code strip_nv (tree_code); -- returns PLUS_EXPR for PLUS_EXPR and PLUSNV_EXPR, etc. I didn't yet come along a need for your last one. Maybe similar to the second one is the requirement to somehow have a test when we want to emit strict-overflow warnings - which we want for the NV codes operating on signed types, possibly using TREE_NO_WARNING for avoiding warnings for NV codes that value-range analysis inserted (and, unfortunately there's no suitable place to put TREE_NO_WARNING on fold arguments ... :/). As of using them always - I will see how it works out. For a start I am able to miscompile gcc after just minimal fold surgery... :/ Thanks, Richard.
