Re: Reduntant move

[Andrew Pinski]

On Tue, May 8, 2018 at 11:07 AM, Dávid Bolvanský
 wrote:
> Hello,
>
> Code example:
> #include 
>
> 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


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Reduntant move

[Dávid Bolvanský]

Hello,

Code example:
#include 

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?
  mov rax, QWORD PTR CSWTCH.0[0+rdi*8]
.L1:
  ret