This blog is updated daily.
A general description is here.
Compilation now uses option ‘-mtune=core2’: this will improve
performance a few percent on recent CPUs at the expense of those which
are several years old.
The 32-bit default build now requires a CPU supporting SSE2 (a Pentium 4 from 2001, AMD Opteron or Athlon 64 from 2003, or later): R can be built from the sources without this requirement: see file ‘MkRules.dist’.
Note that these changes will result in different results on some floating-point calculations (since they affect when extended-precision registers are used): in general they will bring 32-bit Windows closer to results from other platforms (including 64-bit Windows).
Compilation now uses option ‘-mtune=core2’: this will improve performance a few percent on recent CPUs at the expense of those which are several years old.