Fahimeh Yazdanpanah <fahim_yazdan@xxxxxxxxx> wrote on 07/12/2009 13:11:20: > Fahimeh Yazdanpanah <fahim_yazdan@xxxxxxxxx> > 07/12/2009 13:11 > > To > > Ira Rosen/Haifa/IBM@IBMIL > > cc > > gcc-help@xxxxxxxxxxx > > Subject > > Re: Auto-vectorization of if-conversion > > Hello Ira, > > Thank you for your attention. > > But in the loop you modified, there was an other problem to prevent > vectorization : unhandeled data refrences for bb and cc. (The > compiler can not access to bb and cc for several items at the same times). > > Would you please guide me to solve this? It gets vectorized for me with current mainline (and also 4.3) on x86_64-suse-linux with -O2 -ftree-vectorize. Ira > > Thanks in advance, > Best regards, > Fahimeh > > --- On Sun, 12/6/09, Ira Rosen <IRAR@xxxxxxxxxx> wrote: > > > From: Ira Rosen <IRAR@xxxxxxxxxx> > Subject: Re: Auto-vectorization of if-conversion > To: "Fahimeh Yazdanpanah" <fahim_yazdan@xxxxxxxxx> > Cc: gcc-help@xxxxxxxxxxx > Date: Sunday, December 6, 2009, 7:38 AM > > > > > gcc-help-owner@xxxxxxxxxxx wrote on 03/12/2009 17:16:42: > > > Fahimeh Yazdanpanah <fahim_yazdan@xxxxxxxxx> > > Sent by: gcc-help-owner@xxxxxxxxxxx > > > > 03/12/2009 17:16 > > > > To > > > > gcc-help@xxxxxxxxxxx > > > > cc > > > > Subject > > > > Auto-vectorization of if-conversion > > > > Hello, > > > > I am trying to vectorize this loop with gcc-4.4.2 under 64-bit > linuxubuntu : > > > > for (i = 0; i < 1024; i++) > > d[i] = (a[i] > 0 ? b[i] : c[i]); > > > > but it is not vectorized. For compiling that, I use these flags: > > gcc -O3 -fprefetch-loop-arrays -lstdc++ -ftree-vectorize -ftree- > > vectorizer-verbose=2 -ffast-math -mfpmath=sse -march=core2 > > > > according to http://gcc.gnu.org/projects/tree-ssa/vectorization.html > > , it must be vectorized. Would you please tell me what I do wrong? > > The if-conversion pass fails here because of speculative loads of b and c. > Taking the loads outside of condition allows if-conversion and makes the > loop vectorizable: > > for (i = 0; i < 1024; i++) > { > bb = b[i]; > cc = c[i]; > d[i] = (a[i] > 0 ? bb : cc); > } > > Ira > > > > > Thanks in advance, > > Best regards, > > Fahimeh > > > > > > > > > > > > >
