Why doesn’t Julia fma automatically?

[Palli]

Where did this idea come from that C and C++ do FMA automatically?

From Clang, I assume that means C and C++.

See my comment above, and where I’ve answered you on that before (I confirmed personally for Clang for RISC-V with Godbolt):

X * y + z does not automatically use FMA instruction

EDIT: That’s just not true in all cases. Clang does it by default depending on the arch, e.g. uses fmadd.d for RISC-V rv64gc clang 14.0.0 (changed from older versions; same change for 32-bit). It’s not only for -O1, also with -O0, or no options which I assume is the same. [It’s just that I overlooked when looking at boilerplate, the adds you see then are not for the floating point.] That’s not entirely true, depending on what you mean by you “asked for” it, and “by default”. I see I can get it…

The C standard permits intermediate floating-point results within an expression to be computed with more precision than their type would normally allow. This permits operation fusing, and Clang takes advantage of this by default.

I believe Clang has an exeptions to its new default for x86… at least for now.

@StefanKarpinski

which is local to a compilation unit

Julia doesn’t have such, except well packages (precompiled by now), why I proposed a possible exception for them/libraries.