https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68590
--- Comment #10 from Eric Botcazou <ebotcazou at gcc dot gnu.org> --- > So the original compliant was that if we do that we pessimize code-gen > because we un-CSE a possibly large sub-expression. Then maybe the "possibly large sub-expression" should be taken into account. We already try by means of skip_simple_arithmetic, but it's too simple. > So you say that any tree-shared expr is only expanded once (as if it were > wrapped in a save-expr)? No, it will be reexpanded if it has no TREE_SIDE_EFFECTS. What I'm saying is that you control it by means of TREE_SIDE_EFFECTS. > Oh, so fold is performing CSE here? Shouldn't _that_ folding not set > TREE_SIDE_EFFECTS on the SAVE_EXPR? Instead of forcing it on every user... It's not just fold, it's the way SAVE_EXPR works in GENERIC. You need to be able to control when the variable is initialized at run time, otherwise it's a recipe for disaster.
