On 25 February 2014 10:08, Kyrill Tkachov <kyrylo.tkac...@arm.com> wrote: > Hi all, > > The problem solved in this patch is that when gcc is configured with > --with-arch=armv8-a gcc will go into aarch64-arches.def, pick the > representative CPU (Cortex-A53 for ARMv8-A) and use that CPUs ISA flags. Now > that we specified that Cortex-A53 has CRC and crypto though, this means that > gcc will choose by default to enable CRC and Crypto. > > What it should be doing though is to use the 4th field in the AARCH64_ARCH > macro that specifies the ISA flags implied by the architecture. This patch > does that by looking in aarch64-arches.def and extracting the 4th field > appropriately and using that as the ext_mask when processing a --with-arch > option. > > Furthermore, if no --with-arch or --with-cpu directives are specified > config.gcc will set TARGET_DEFAULT_CPU to TARGET_CPU_generic. What it should > be doing, is leaving it undefined so that the backend in aarch64.h can > define its own default with the correct ISA options (currently we have this > scheme where the TARGET_CPU_<core> is encoded in the first 6 bits of > TARGET_DEFAULT_CPU and the ISA flags are encoded in the upper part of it. We > should clean that up in the next release). Before this patch, the code in > aarch64.h that does that initialisation was never even exercised because > TARGET_CPU_DEFAULT was always defined by config.gcc no matter what! > config.gcc defined it as TARGET_CPU_generic but without encoding the > appropriate ISA flags in the upper bits, leading to a cpu configured without > fp or simd. > > After a discussion with Richard, this patch sets the default CPU (if no > -mcpu,-march,--with-cpu,--with-arch is given) to be generic+fp+simd. The > generic CPU already schedules like the Cortex-A53, so it should give a > decent generic tuning. > > This patch should improve the current situation a bit. > With this patch: > - If --with-arch=armv8-a is specified we will use generic+fp+simd as the CPU > (without the patch it's cortex-a53+fp+simd+crc+crypto) > - If no arch or cpu options specified anywhere, we will use the > generic+fp+simd CPU (without the patch it would be just generic) > > Tested aarch64-none-elf on a model and checked the .cpu directive in the > generated assembly for a variety of --with-cpu, --with-arch combinations > > I'm proposing this patch as an alternative to > http://gcc.gnu.org/ml/gcc-patches/2014-02/msg01072.html.
- if test x$target_cpu_cname = x + if test x"$target_cpu_cname" != x I think the addition of quoting here is orthogonal to the issue you are fixing. There are several other references to target_cpu_cname in config.gcc none of which are quoted, so I guess either they should all be quoted, or not, and if they are it is a separate patch. That nit aside I think the rest of the patch makes sense for stage-4. Give the RM's 24 hours to comment otherwise drop the above nit and commit. Cheers /Marcus
