[GDC] Evaluation order: Please update the dmd backend

[Timon Gehr]

On 04/01/2014 08:40 PM, Sarath Kodali wrote:
> ...
>
> The evaluation order of assign operators should not be LTR as they have
> right associativity. In "a = b = c", c has to be evaluated first, then b
> and then a. Similarly, in "a = b + c", "b+c" has to be evaluated first
> before a is evaluated. Otherwise it will be very confusing, that in some
> cases it is LTR and in some it is RTL.

Note that this is after a paragraph that suggests to make evaluation in 
some cases LTR and in some RTL.

> Other binary operators like "+" have left associativity, and hence
> evaluation for these should be LTR as mentioned in D spec.
> ...

What's the presumed relation between associativity and evaluation order?

In particular, the ternary operator ?: is right associative. How on 
earth are you going to evaluate it right to left?

> The C spec requires that the function arguments are to be pushed in RTL
> order.

[citation needed]

> The DMD codegen uses pushl x86 instructions for pushing args. If the
> frontend changes the func args evaluation order to LTR, then the backend
> has to be modified  to use mov x86 instructions as is done by gcc codegen.
>
> - Sarath
>

The backend does not necessarily have to be modified to achieve this.