https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62006
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> --- It looks ok what PRE does (it's not really a partial partial redundancy but a full redundndancy). The bug also reproduces with -O2 -ftree-partial-pre. Disabling loop optimizations and cddce2 hides the bug. With PPRE enabled CDDCE2 removes the stores to D.46421.diff (again I see nothing wrong with doing that). Btw, this all happens in _M_range_initialize. (-fno-strict-aliasing fixes the bug as well). Note that I see stores as OffPtrBase to automatic objects: - MEM[(struct OffPtrBase *)&D.46421].diff = _70; and loads from OffPtr via this: _16 = &MEM[(struct OffPtr *)this_4(D)].D.43564; or remaining stores: MEM[(struct OffPtrBase *)this_4(D) + 16B].diff = iftmp.15_41; I also see: _74 = (sizetype) _47; iftmp.10_75 = &D.46429.D.43564 + _74; __last.3_77 = (long int) iftmp.10_75; __first.4_78 = (long int) &D.46430.D.43564; _79 = __last.3_77 - __first.4_78; which effectively subtracts two unrelated addresses of automatic objects (boooo - undefined behavior!) I think the testcase is simply bogus. Can you explain what the "fancy" pointers do? Disabling points-to analysis also "fixes" the testcase. Note that with points-to analysis you cannot reach any other object with offsetting the address of an object.
