On Thu, Aug 30, 2018 at 7:39 PM Martin Sebor <mse...@gmail.com> wrote: > > On 08/30/2018 11:22 AM, Richard Biener wrote: > > On August 30, 2018 6:54:21 PM GMT+02:00, Martin Sebor <mse...@gmail.com> > > wrote: > >> On 08/30/2018 02:35 AM, Richard Biener wrote: > >>> On Thu, Aug 30, 2018 at 2:12 AM Martin Sebor <mse...@gmail.com> > >> wrote: > >>>> > >>>> The attached patch adds code to work harder to determine whether > >>>> the destination of an assignment involving MEM_REF is the same > >>>> as the destination of a prior strncpy call. The included test > >>>> case demonstrates when this situation comes up. During ccp, > >>>> dstbase and lhsbase returned by get_addr_base_and_unit_offset() > >>>> end up looking like this: > >>> > >>> "During CCP" means exactly when? The CCP lattice tracks copies > >>> so CCP should already know that _1 == _8. I suppose during > >>> substitute_and_fold then? But that replaces uses before folding > >>> the stmt. > >> > >> Yes, when ccp_finalize() performs the final substitution during > >> substitute_and_fold(). > > > > But then you shouldn't need the loop but at most look at the pointer SSA > > Def to get at the non-invariant ADDR_EXPR. > > I don't follow. Are you suggesting to compare > SSA_NAME_DEF_STMT (dstbase) to SSA_NAME_DEF_STMT (lhsbase) for > equality? They're not equal.
No. > The first loop iterates once and retrieves > > 1. _8 = &pb_3(D)->a; > > The second loop iterates three times and retrieves: > > 1. _1 = _9 > 2. _9 = _8 > 3. _8 = &pb_3(D)->a; > > How do I get from _1 to &pb_3(D)->a without iterating? Or are > you saying to still iterate but compare the SSA_NAME_DEF_STMT? I say you should retrieve _8 = &pb_3(D)->a immediately since the copies should be propagated out at this stage. > Martin > > > > > Richard. > > > >> Martin > >> > >>> > >>> So I'm confused. > >>> > >>>> > >>>> _8 = &pb_3(D)->a; > >>>> _9 = _8; > >>>> _1 = _9; > >>>> strncpy (MEM_REF (&pb_3(D)->a), ...); > >>>> MEM[(struct S *)_1].a[n_7] = 0; > >>>> > >>>> so the loops follow the simple assignments until we get at > >>>> the ADDR_EXPR assigned to _8 which is the same as the strncpy > >>>> destination. > >>>> > >>>> Tested on x86_64-linux. > >>>> > >>>> Martin > > >
