Phoronix article: https://www.phoronix.com/scan.php?page=news_item&px=FC-LLVM-...

1. A portable binary where only individual SIMD operations are optimized for all targets. 2. Building the optimized binary for every target architecture when needed (either by the user or by the binary distributor).

Concern with (1) is, as the number of dynamically called functions (or decided by if-else nests) increases the quality of the generated code reduces for any architecture. Basically, compiler will be left with opaque unrecognizable functions which restricts even the target independent optimizations (Like, GVN, CSE Constant propagation etc).

Let's say, if the user writes a SIMD program which contains full of dynamically called functions (which are opaque to the compiler), doesn't it impact the performance heavily?

Isn't taking the compiler support for optimizing the SIMD operations necessary rather than writing wrapper libraries ? For example, lowering the SIMD operation calls to the existing vectorized math libraries which are recognizable by the compilers ( Example: sin(), cos(), pow() in libm ).

What are the use cases for having multiple alternates in the same binary? Why not decide them during the compile time for the given architecture?

If portability is the concern here, wouldn't it lead to sub-optimal code anyway?