Re: Reduntant move

[Andrew Pinski]

On Tue, May 8, 2018 at 11:07 AM, Dávid Bolvanský
<david.bolvan...@gmail.com> wrote:
> Hello,
>
> Code example:
> #include <stdio.h>
>
> char * a(int e) {
>     char * s;
>     switch (e) {
>         case 0:
>             s = "0";
>             break;
>         case 1:
>             s = "1";
>             break;
>         case 2:
>             s = "2";
>             break;
>         default:
>             s = "def";
>             break;
>     }
>
>     return s;
> }
>
>
> GCC 8.1:
> a:
>   mov eax, OFFSET FLAT:.LC0
>   cmp edi, 2
>   ja .L1
>   mov edi, edi  <------ redundant?

Is a zero extend from edi to rdi.  Yes it is written as a mov but it
causes the cleaning of the top 32bits of rdi.

Thanks,
Andrew

PS gcc-bugs@ is really for the automated bugzilla emails so sending it
to gcc-bugs@ might not get that much attention.

>   mov rax, QWORD PTR CSWTCH.0[0+rdi*8]
> .L1:
>   ret<div id="DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2"><br />
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