When should I use __forceinline instead of inline?

Question

Visual Studio includes support for __forceinline. The Microsoft Visual Studio 2005 documentation states:

The __forceinline keyword overrides the co

Answer 1

For SIMD code.

SIMD code often uses constants/magic numbers. In a regular function, every const __m128 c = _mm_setr_ps(1,2,3,4); becomes a memory reference.

With __forceinline, compiler can load it once and reuse the value, unless your code exhausts registers (usually 16).

CPU caches are great but registers are still faster.

P.S. Just got 12% performance improvement by __forceinline alone.