[Bug 248] Regression: Call result not properly saved when calling a vtbl function

[via D.gnu]

http://bugzilla.gdcproject.org/show_bug.cgi?id=248

--- Comment #2 from Iain Buclaw <ibuclaw at gdcproject.org> ---
(In reply to Johannes Pfau from comment #0)
> Reduced from a DDMD build regression:
> 
> We've got a function getMemtype which has side effects and returns a class
> object Bar which has a virtual function isintegral. The function is called
> in this way: getMemtype().isintegral(). In this call the return value of
> getMemtype, the reference to a Bar object, is needed twice: Once to get the
> vtbl entry for isintegral and once to pass the object reference as the this
> pointer for isintegral. I guess the result of the getMemtype call is not
> saved properly. We can certainly see that the getMemType function executes
> twice.
> 
> @Iain I'll assign this to you as you are more familiar with this code.
> 
> ---------------------------------------------------
> import std.stdio;
> 
> class Bar
> {
>     bool isintegral()
>     {
>         return false;
>     }
> }
> 
> class Symbol
> {
>     Bar getMemtype()
>     {
>         writeln("foo");
>         return new Bar();
>     }
> }
> 
> class Enum
> {
>     Symbol sym;
>     bool isintegral()
>     {
>         return sym.getMemtype().isintegral();
>     }
> }
> 
> void main()
> {
>     Enum e = new Enum();
>     e.sym = new Symbol();
>     e.isintegral();
> }
> ---------------------------------------------------

It looks like the expression is saved, but the saved expression is not re-used
when passed as a parameter.

Analogous to:

SAVE_EXPR<this.sym.getMemtype(this.sym)>.isintegral(this.sym.getMemtype(this.sym));

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