On Thu, Aug 16, 2012 at 1:43 PM, Gopalasubramanian, Ganesh <ganesh.gopalasubraman...@amd.com> wrote: >> This won't work, since we have to prefer FMA3 also in case when only "-mfma >> -mfma4" without -mtune=XX is used. >> We can add TARGET_FMA_BOTH though, but I doubt there will ever be target >> that implements both insn sets without preferences. > > Preferring FMA3 over FMA4 might not do good always. For instance, with > increased register pressure FMA3 can be used. > But, when we have more registers at our disposal, fma4 if used might do good > by avoiding extra reload. > IMO, when preference of FMA instructions is adjudged by register pressure, > we may need some functionality to support that. > > So, ideally for bdver2, we like to have both fma and fma4 getting generated > with options "-mfma -mfma4".
Yes, now it can also work that way. Current insn generation can be trivially changed now, just change "fma4" condition for "enabled" attribute in i386.md. I will wait for your recommendation. Uros.
