RE: [avr-gcc-list] Inconsisten behaviour of switch statement

[Schwichtenberg, Knut]

Hi, 

> -----Original Message-----
> From: 
> address@hidden
> g 
> [mailto:address@hidden
ongnu.org] On Behalf Of Joerg Wunsch
> Sent: Tuesday, March 27, 2007 7:10 AM
> To: address@hidden
> Subject: Re: [avr-gcc-list] Inconsisten behaviour of switch statement
> Knut, can you provide us an example that reproduces the problem?
Okay, attached to my first posting there was my exapmle. I strip it to
an overview:

volatile uint8_t minute;

switch (minute)
      {
      case 0:
      case 15:
      case 30:
      case 45:
            dosomething();
         break;
      default:
         break;
      }
Is compiled to:

.LM2:                   
                lds r24,minute      
                clr r25             
                cpi r24,15          
                cpc r25,__zero_reg__
                breq .L6            
.LM3:                   
                cpi r24,16          
                cpc r25,__zero_reg__
                brge .L10           
                or r24,r25          
                breq .L6            
                rjmp .L2            
.L10:                   
                cpi r24,30          
                cpc r25,__zero_reg__
                breq .L6            
                sbiw r24,45         
                brne .L2            
.L6:                    

and a 0 to 24 switch example:

volatile uint8_t sec25;
   switch (sec25) {
      case 0: doa(); break;
        case 1: doa(); break;
      case 2: doa(); break;
      case 3: doa(); break;
// Mostly all other elemets are in use 
...
      case 24: doa(); break;
        default: break;

is compiled to:
                lds r24,sec25                               
                clr r25                                     
                clr r26                                     
                clr r27                                     
                movw r30,r24                                
                sbiw r24,25                                 
                brsh .L11                                   
                subi r30,lo8(-(pm(.L37)))                   
                sbci r31,hi8(-(pm(.L37)))                   
                lsl r30                                     
                rol r31                                     
                lpm __tmp_reg__,Z+                          
                lpm r31,Z                                   
                mov r30,__tmp_reg__                         
                ijmp                                        
        .data                                         
        .section .progmem.gcc_sw_table, "a", @progbits
        .p2align 1                                    
.L37:                                           
                .word pm(.L12)                              
                .word pm(.L16)                              
                .word pm(.L33)                              
                .word pm(.L24)                              
                .word pm(.L33)                              
                .word pm(.L34)                              
                .word pm(.L33)                              
                .word pm(.L22)                              
                .word pm(.L33)                              
                .word pm(.L24)                              
                .word pm(.L33)                              
                .word pm(.L34)                              
                .word pm(.L33)                              
                .word pm(.L11)                              
                .word pm(.L33)                              
                .word pm(.L29)                              
                .word pm(.L33)                              
                .word pm(.L34)                              
                .word pm(.L33)                              
                .word pm(.L11)                              
                .word pm(.L33)                              
                .word pm(.L34)                              
                .word pm(.L11)                              
                .word pm(.L11)                              
                .word pm(.L35)                              
        .text                                         

Here are the examples. 

Cheers

Knut

BTW: casting of the constant, the variable or both does not convince gcc
to use a byte compare.