[sdcc-devel] [ sdcc-Bugs-1229346 ] Array and temporary bugs

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Bugs item #1229346, was opened at 2005-06-29 10:00
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Category: pic14 target
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Simon (smcauliffe)
Assigned to: Nobody/Anonymous (nobody)
Summary: Array and temporary bugs

Initial Comment:
Here's a small snippet of code that reproduces two
simple bugs. Sorry if this has already been reported, I
couldn't find the information elsewhere though.

#define __16f627
#include <pic/pic16f627.h>

unsigned char buffer[16];

int main()
{
  if (buffer[0] == 0) {
    PORTA = buffer[1];
  }

  if (buffer[0] == 1) {
    PORTA = buffer[2];
  }

  return 0;
}

The first bug is caused by having two if statements (or
a switch statement).  It causes a temporary to be
allocated but nothing is ever assigned to the temporary
variable.  Having only one if statement doesn't
allocate a temporary and then it works.

The second bug is PORTA not being assigned.  If
assigning a constant, it works fine, but assigning from
the array results in no code.

The resulting assembly is below (slightly edited for
brevity):

                                           ;entry: 
_main       ;Function start
                                           ;2 compiler
assigned registers:
                                           ;   r0x21
                                           ;   s0x7F
                                           _main      
 ;Function start
                                           ;  if
(buffer[0] == 0) {
000005   1283     bcf   0x3, 0x5                BANKSEL
r0x21
000006   1703     bsf   0x3, 0x6
000007   0830     movf  0x30, w                 MOVF  
 r0x21,W
000008   1d03     btfss 0x3, 0x2                BTFSS 
 STATUS,2
000009   280a     goto  0xa                     GOTO  
 _00106_DS_
                                           _00106_DS_
                                           ;  if
(buffer[0] == 1) {
00000a   0b30     decfsz        0x30, w               
 DECFSZ  r0x21,W
00000b   280c     goto  0xc                     GOTO  
 _00108_DS_
                                           _00108_DS_
                                           ;  return 0;
00000c   3000     movlw 0                       MOVLW 
 0x00
00000d   00ff     movwf 0x7f                    MOVWF 
 s0x7F
00000e   3000     movlw 0                       MOVLW 
 0x00
00000f   0008     return                        RETURN

At address 7, the temporary is being used, but hasn't
yet been assigned to from buffer[0]

And also, as you can see, there is no mention of
assigning to PORTA (there would be if it was a constant
assignment).  Perhaps it's being optimised away?

In any case, I hope these are useful.  Please drop me
an email at S.M...@dt... if I can provide any
furtherr information or if I can be of any assistance
in debugging the compiler.

Thanks.


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