On Fri, Oct 28, 2011 at 12:16 PM, Richard Guenther <rguent...@suse.de> wrote: > On Thu, 27 Oct 2011, Uros Bizjak wrote: > >> Hello! >> >> > Here's a patch for PR47698, which is about CMOV should not be >> > generated for memory address marked as volatile. >> > Successfully bootstrapped and passed make check on >> > x86_64-unknown-linux-gnu. >> >> >> PR rtl-optimization/47698 >> * config/i386/i386.c (ix86_expand_int_movcc) prevent CMOV generation >> for volatile mem >> >> PR rtl-optimization/47698 >> * gcc.target/i386/47698.c: New test >> >> Please use punctuation marks and correct capitalization in ChangeLog entries. >> >> OTOH, do we want to fix this per-target, or in the middle-end? > > The middle-end pattern documentation does not say operands 2 and 3 > are not evaluated if they do not end up being stored, so a middle-end > fix is more appropriate. > > Richard. >
I have two observations: - the code for CMOV is under #ifdef in the mddle-end, which is explicitly marked as "have to be removed" (ifcvt.c:1446) - I have no clear evidence all platforms that support conditional move have the same semantics that lead to the PR I think the best way to address both concerns is to implement code that relies on а new hookup "volatile-safe CMOV" that is false by default. regards, Sergos
