https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65752
--- Comment #35 from Chung-Kil Hur <gil.hur at sf dot snu.ac.kr> --- (In reply to rguent...@suse.de from comment #34) > On Sat, 23 May 2015, gil.hur at sf dot snu.ac.kr wrote: > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65752 > > > > --- Comment #33 from Chung-Kil Hur <gil.hur at sf dot snu.ac.kr> --- > > Dear Richard, > > > > Thanks for the detailed response. > > > > I have a suggestion for a solution of the problem, which is based on my > > paper > > to appear at PLDI 2015. > > > > * A Formal C Memory Model Supporting Integer-Pointer Casts. > > Jeehoon Kang, Chung-Kil Hur, William Mansky, Dmitri Garbuzov, Steve > > Zdancewic, Viktor Vafeiadis. > > http://sf.snu.ac.kr/gil.hur/publications/intptrcast.pdf > > > > The suggestion is simple. > > You do not need to turn off the phiopt optimizations. > > We propose to slightly change the following assumption. > > > > > PTA considers that all pointers coming from integer constants > > > point to global memory only. > > > > Here, if you change this as follows, you can solve the problem. > > > > * All pointers coming from integer constants can point to only global memory > > and > > local variables whose addresses have been cast to integers. > > Ok, so you basically add a 2nd class of "escaping". So in GCC PTA > terms you'd add a new ESCAPE-like 'INTEGER' variable with > > INTEGER = NONLOCAL > > and add > > INTEGER = x > > constraints for each > > .. = (integer-type) &x > > conversion and for the reverse > > ptr = (pointer-type) i > > add > > ptr = INTEGER > > > Also, we expect that this would not decrease the optimization performance of > > GCC very much because those variables whose addresses have been cast to > > integers tend to be escaped (e.g. passed to a hash function, or stored in > > the > > memory). > > Well - the above basically makes _all_ pointers converted from integers > point to non-local memory, it also basically globs all pointers > converted from integers into a single equivalence class. Yes, this is right. > So I think you underestimate the effect on optimization (but I may > overestimate the effect on optimization of not simply making all > pointers converted from integers point to all globals and all > address-taken locals, aka ANYTHING in GCC PTA terms) Just one minor correction: all address-taken locals -> all address-taken-and-cast-to-integer locals Yes, I agree. In order to understand the effect, we need some empirical evidence. I am interested in this direction. So, I wonder what benchmarks you usually use to check the effect of compiler optimizations. More specifically, are SPEC benchmarks enough? or do you use some other benchmarks too? Thanks!
