Hi All,
It seems gcc (may be from 5) optimizes the global variable's accesses though standard C functions are called in-between the accesses.
Example:
1 #include <stdlib.h>
2
3 struct __freelist {
4 size_t sz;
5 struct __freelist *nx;
6 };
7
8 extern char *__brkval;
9 extern struct __freelist *__flp;
10 int main(void)
11 {
12 char *p, *p1;
13
14 p = malloc(16);
15 if (!p)
16 return 1;
17
18 /* releasing 6 bytes creates a new free chunk */
19 p1 = realloc(p, 10);
20 if (p != p1)
21 return 2;
22
23 p = p1 + 10;
24 if (__brkval != p)
25 return 3;
26
27 /* use the last free chunk */
28 p1 = malloc(4);
29 if (!p1)
30 return 4;
31
32 p = malloc(10);
33 if (!p)
34 return 6;
35
36 /* force creation of a new minimal free chunk (sz = 3), which
37 will be returned from heap then */
38 p1 = realloc(p, 5);
39 if (p != p1)
40 return 7;
41
42 p = p1 + 5;
43 if (__brkval != p)
44 return 8;
45
46 return 0;
47 }
This example is derived from avr-libc's test.
Ref: http://svn.savannah.nongnu.org/viewvc/trunk/avr-libc/tests/simulate/regression/bug-27242.c?revision=2131&root=avr-libc&view=markup
avr-gcc (used gcc-5.2) optimizes the __brkval access at line 43 by reusing the registers which is loaded with __brkval value. Is that expected?
When -ffreestanding option is enabled, the global variable is loaded from memory for line #43.
Or is there any specific option to avoid optimizing such variable access?
Regards,
Pitchumani
