"Ye, Joey" <joey...@intel.com> writes: > From: Ian Lance Taylor [mailto:i...@google.com]: >> Therefore, I propose that we do the following: >> >> 1) Introduce __attribute__ ((aligned (scalar))). This will be >> documented as having a fixed value for each ABI. The value will be >> guaranteed to be sufficient to hold any ordinary non-vector type. >> The default will be BIGGEST_ALIGNMENT. The value for the >> x86/x86_64 will be 128. >> >> 2) Introduce __attribute__ ((aligned (max))). This will be documented >> as having the largest value available for any version of the >> architecture, and thus in particular it may change if new versions >> of the architecture are released. The value will not change based >> on command line options which do not change the ABI; that is, if it >> is possible to link together two files compiled with different set >> of command line options and expect the result to work, then those >> command line options must not change the value of this attribute. >> The value will be guaranteed to be sufficient to hold any type, >> including any vector type. The default will be BIGGEST_ALIGNMENT. >> The value for the x86/x86_64 will (presumably) be 256. > To me "new version of x86 architecture are released" usually means > "change based on command line option". How about the default value > grow to 512 or even higher in future?
There is a command line option change, sure, but in general, as far as I know, files compiled with -march=NEW can be linked with files compiled with -march=OLD, and the result is expected to work. If that is not the case--if files compiled with -march=avx and -march=i386 (or -march=nocona) can not be linked together and work--then there is no problem here. Ian
