https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78035
--- Comment #10 from rguenther at suse dot de <rguenther at suse dot de> --- On Wed, 2 Nov 2016, krister.walfridsson at gmail dot com wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78035 > > krister.walfridsson at gmail dot com changed: > > What |Removed |Added > ---------------------------------------------------------------------------- > CC| |krister.walfridsson at gmail > dot c > | |om > > --- Comment #9 from krister.walfridsson at gmail dot com --- > Doesn't this just introduce more inconsistencies in the compiler? For example > > extern int a; > extern int b; > > int foo(void) > { > a = 1; > b = 5; > a++; > return &a != &b; > } > > optimizes to > > foo: > movl $a, %eax > movl $5, b(%rip) > movl $2, a(%rip) > cmpq $b, %rax > setne %al > movzbl %al, %eax > ret > > That is, the accesses to a and b are optimized as if they are distinct, even > though the compiler keeps the comparison of the addresses. > > I cannot think of a reasonable use case where you must handle comparisons of > the addresses as currently implemented while allowing other optimizations as > if > the objects are distinct, so I'd say the bug from the original description is > that we were "being too conservative in bar"... I opened this bug for the inconsistency in address comparisons which now can utilize points-to analysis. This part is fixed now. Yes, for alias analysis we are less conservative than when optimizing address comparisons ... but it appears that this is on purpose.
