------- Comment #4 from bigotp at acm dot org 2010-08-11 22:54 ------- I don't see that the const qualifier should be relevant: doesn't it simply indicate that the code is not permitted to write through that lvalue? (FWIW, the real code uses a memory mapped address and the const qualifier was placed on the address declaration by the chip manufacturer. I assume that a write to the location may be interpreted as a command to the hardware to self-destruct.)
Given that, the existing behavior appears to be a clear violation of the requirement that volatile accesses not be re-ordered across sequence points. In concept, I like rguenth's solution (which I haven't tested), as it fits with the documented semantics of MEM_READONLY_P indicating "not modified during the lifetime of the program", something that certainly can't be said of any readable volatile object. That the RTL flag is stored in a field named "unchanging" is a lot more clear than "READONLY". I think that approach eliminates the need to muck with any of those other places where the same problem might be occurring. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45235
