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Date: Thu, 01 Nov 2007 13:44:00 -0000
Subject: [Bug c/33970]  New: Missed optimization using unsigned char loop variable
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From: "henning dot m at insightbb dot com" <gcc-bugzilla@gcc.gnu.org>
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When using an unsigned char in a loop with limited range the variable is
promoted to a 16 bit integer if the variable is passed to another function
within the loop by value. 


Tested using -Os on ATMEGA162:

#include <avr/io.h>


int sub2(uint8_t);

int main(void) {

static uint8_t  x;
volatile uint8_t y;

while(1)
 {

   for(x=0;x<128; x++)
     {
        y+=sub2(x);
     }
  }

  return 0;
}



int sub2(uint8_t xyz) {

volatile uint8_t abc;

while(xyz < 64)
 {
    xyz++;
    abc+=xyz;
 }
  return abc;
}


-- 
           Summary: Missed optimization using unsigned char loop variable
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: henning dot m at insightbb dot com
 GCC build triplet: WinAVR 20070525
GCC target triplet: avr


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33970