On Wed, 25 Nov 2015, Richard Biener wrote: > On Wed, 25 Nov 2015, Jakub Jelinek wrote: > > > On Wed, Nov 25, 2015 at 03:35:10PM +0100, Marek Polacek wrote: > > > Look how 'x' is duplicated in the result of the pattern, and since > > > (because of > > > the volatile 'e') it has TREE_SIDE_EFFECTS, we need to wrap it in a > > > SAVE_EXPR, > > > which means the convert() produces > > > > > > (short int) (((SAVE_EXPR <c_maybe_const_expr <i> != 0 ? (unsigned short) > > > c_maybe_const_expr <*e > : 0>) > > > ^ (unsigned short) i) & (unsigned short) u > > > ^ (SAVE_EXPR <c_maybe_const_expr <i > != 0 ? (unsigned short) > > > c_maybe_const_expr <*e > : 0>)) > > > > > > What's important is that we end up with a C_MAYBE_CONST_EXPR in a > > > SAVE_EXPR. > > > > > > Down the line, we get into c_process_expr_stmt, where there's > > > > > > expr = c_fully_fold (expr, false, NULL); > > > > > > so we try to fully-fold the whole expression. However, c_fully_fold just > > > gives up when it sees a SAVE_EXPR, so it doesn't scrub out > > > C_MAYBE_CONST_EXPR. > > > It then leaks into the gimplifier and crashes. > > > > Ran into similar issues many times in the past, the main issue is that the C > > FE wants that before c_fully_fold is called on some expression that nobody > > wraps anything into a SAVE_EXPR except by calling c_save_expr. > > So, unless we get rid of that (severe) limitation, we should make sure > > that either match.pd never creates SAVE_EXPRs when called from the "early" > > spots in the C FE, or that it uses c_save_expr instead of save_expr. > > But finding out if you have an expression on which c_fully_fold has been > > already called or not is non-trivial too. > > > > Wonder if we couldn't use some FE specific bit on the SAVE_EXPR to say > > whether c_fully_fold_internal has already processed it or not, and just > > get rid of c_save_expr, in c_fully_fold* recurse into SAVE_EXPRs too, but > > only if that bit is not yet already set, and set it afterwards. > > c_gimplify_expr and SAVE_EXPR_RESOLVED_P would work as well I guess?
Or simply not call fold () from convert () -> convert_to_integer (). Richard.
