Re: [gpsd-dev] register keyword?

From:

Kurt Schwehr

Subject:

Date:

Mon, 22 Jan 2018 16:59:51 -0800

Gary,

I was in C mode the whole time and if you add the pragma for optimization, you will find the results of with and without register are the same.

Don't be fooled by the //

https://godbolt.org/g/3oGTfE

On Mon, Jan 22, 2018 at 3:25 PM, Gary E. Miller <address@hidden> wrote:

Yo Kurt!

On Mon, 22 Jan 2018 15:04:13 -0800
Kurt Schwehr <address@hidden> wrote:

> The general compiler folks consensus is that the optimizers generally
> just ignore register and it's being removed from C++17. Linking
> against C++17 code is my main reason for this.

Uh, this is C code, not C++ code. What are you linking it to?

> But that's why we have https://godbolt.org/ to easily try it out.

Well, that is fun. It also shows the register keyword really helps. Ar
least when I select a C compiler.

> Looking at gcc x86-64 7.2, the assembly without register is shorter.

I see your point in C++ mode, but not in C mode. In C mode the
register keyword is a real win.

> #pragma GCC optimize("O3")
>
> The assembly with and without registers is exactly the same.

Except gpsd does not use -O3. I see similar on -o2, which gpsd does
use, except that optimization will not work for a linked in function.

RGDS
GARY
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