------- Comment #14 from rguenther at suse dot de 2010-09-16 12:51 ------- Subject: Re: Missed devirtualization
On Thu, 16 Sep 2010, hubicka at ucw dot cz wrote: > ------- Comment #13 from hubicka at ucw dot cz 2010-09-16 12:48 ------- > Subject: Re: Missed devirtualization > > > I'm lost in this PR - for what testcase what statement needs folding > > (and what pending patches do I need to apply to see that)? > PR is tracking missed optimization in the testcase in comment 0. > > There are two issues > > > > 1) OBJ_TYPE_REF folding should handle it. For that we seem to need to > evern call fold on > OBJ_TYPE_REF(D.2210_2;&d.D.2108->0) (&d.D.2108); > this you can see on mainline > > 2) generic folding should work it out the hard way. I.e. for: > MEM[(struct B *)&d]._vptr.B = &_ZTV1B[2]; > d.D.2108._vptr.B = &_ZTV1D[2]; > D.2210_2 = _ZTV1D[2]; > OBJ_TYPE_REF(D.2210_2;&d.D.2108->0) (&d.D.2108); > there is nothing that prevents us to resolve _ZTV1D[2] into pointer to Run (by > looking into initializer of vtable variable) and then take OBJ_TYPE_REF away > since it is pointless when first operand is known function. > > With patch http://gcc.gnu.org/ml/gcc-patches/2010-09/msg01190.html we closer > in > a way that .vpr1 dump has: > MEM[(struct B *)&d]._vptr.B = &_ZTV1B[2]; > d.D.2078._vptr.B = &_ZTV1D[2]; > D.2179_1 = &_ZTV1D[2]; > D.2180_2 = (int (*__vtbl_ptr_type) (void)) Run; > OBJ_TYPE_REF(D.2180_2;&d.D.2078->0) (&d.D.2078); > > Somewhere I have patch that adds OBJ_TYPE_REF folding into CCP (so when first > argument is function pointer, we just fold into direct call). I will update it > and submit after http://gcc.gnu.org/ml/gcc-patches/2010-09/msg01190.html > is resolved. Then still there is problem that resolution comes late > since we need FRE to fold > d.D.2078._vptr.B = &_ZTV1D[2]; > D.2179_1 = d.D.2078._vptr.B > and FRE is not run early (and we should devirutalize everything early > to get inlining) > > > > 1) is priority IMO (at moment we make amazingly little devirtualization at > Mozilla, about 20 calls). > 2) is just side effect of my attempt to get folding working that I run into > while looking into kernel poor man C vtables (and ours targhooks). 1) should be fixed by using fold_stmt in gimplify_call instead of just fold_call_expr. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45605
