[Issue 5688] Poor optimization of (long & 1)

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http://d.puremagic.com/issues/show_bug.cgi?id=5688



--- Comment #2 from Don <clugdbug at yahoo.com.au> 2011-03-03 17:52:46 PST ---
(In reply to comment #1)
> Interestingly, if the code is written as:
> 
> bool foo(long v)
> {
>     return  (v & 1) == 1;
> }
> 
> the code generated is:
> 
>                 mov     EAX,4[ESP]
>                 mov     EDX,8[ESP]
>                 and     EAX,1
>                 xor     EDX,EDX
>                 ret     8

I noticed that. And even though that's better, both uses of EDX are completely
unnecessary.
Changing  cgelem.c, elcmp(), around line 3350 to this:

                    case 8:
-                        e = el_una(OP64_32,TYlong,e);
+                        e->E1 = el_una(OP64_32,TYint,e->E1);
+                        e->E2 = el_una(OP64_32,TYint,e->E2);
                        break;
makes it create optimal code, although that's probably incorrect for 64 bits.
The way elcmp() works looks pretty bizarre to me.
But it's the return ( v & 1); case that is the primary problem.

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