On Thu, Oct 26, 2023 at 07:28:35AM +0000, Xiang Gao wrote: > On Wed, 25 Oct, 2023 at 10:43:25 -0500, Nathan Bossart wrote: >>+# Use ARM VMULL if available and ARM CRC32C intrinsic is avaliable too. >>+if test x"$USE_ARMV8_VMULL" = x"" && (test x"$USE_ARMV8_CRC32C" = x"1" || >>test x"$USE_ARMV8_CRC32C_WITH_RUNTIME_CHECK" = x"1"); then >>+ if test x"$pgac_armv8_vmull_intrinsics" = x"yes"; then >>+ USE_ARMV8_VMULL=1 >>+ fi >>+fi > >>Hm. I wonder if we need to switch to a runtime check in some cases. For >>example, what happens if the ARMv8 intrinsics used today are found with the >>default compiler flags, but vmull_p64() is only available if >>-march=armv8-a+crypto is added? It looks like the precedent is to use a >>runtime check if we need extra CFLAGS to produce code that uses the >>intrinsics. > > We consider that a runtime check needs to be done in any scenario. > Here we only confirm that the compilation can be successful. > A runtime check will be done when choosing which algorithm. > You can think of us as merging USE_ARMV8_VMULL and > USE_ARMV8_VMULL_WITH_RUNTIME_CHECK into USE_ARMV8_VMULL.
Oh. Looking again, I see that we are using a runtime check for ARM in all cases with this patch. If so, maybe we should just remove USE_ARV8_CRC32C_WITH_RUNTIME_CHECK in a prerequisite patch (and have USE_ARMV8_CRC32C always do the runtime check). I suspect there are other opportunities to simplify things, too. -- Nathan Bossart Amazon Web Services: https://aws.amazon.com
