On Monday, 4 April 2016 at 16:21:15 UTC, Marco Leise wrote:
Am Mon, 04 Apr 2016 14:02:03 +0000
schrieb 9il <ilyayaroshe...@gmail.com>:
- On amd64, whether floating-point math is handled by the FPU
or SSE. When emulating floating-point, e.g. for
float-to-string and string-to-float code, it is useful to
know where to get the active rounding mode from, since they
may differ and at least GCC has a switch to choose between
both.
- For compile time enabling of SSE4 code, a version define is
sufficient. Sometimes we want to select a code path at
runtime. For this to work, GDC and LDC use a conservative
feature set at compile time (e.g. amd64 with SSE2) and tag
each SSE4 function with an attribute to temporarily elevate
the instruction set. (e.g. @attribute("target", "+sse4"))
If you didn't tag the function like that the compiler would
error out, because the SSE4 instructions are not supported
by a minimal amd64 CPU.
To put this to good use, we need a reliable way - basically
a global variable - to check for SSE4 (or POPCNT, etc.). What
we have now does not work across all compilers.
@attribute("target", "+sse4")) would not work well for BLAS. BLAS
needs compile time constants. This is very important because BLAS
can be 95% portable, so I just need to write a code that would be
optimized very well by compiler. --Ilya
