[Bug rtl-optimization/17972] const/pure functions result in bad asm

[mostrows at watson dot ibm dot com]

------- Additional Comments From mostrows at watson dot ibm dot com  2004-10-13 23:11 -------
Subject: Re:  const/pure functions result in
	bad asm

Here is simpler code that demonstrates the problem.  Note, no loops
involved.  Further below is compilation and objdump with and without
DBUG. 

struct thread_info {
    int preempt_count;
};

#ifdef BUG
static inline struct thread_info *cti(void) 
    __attribute__((pure));
#else
static inline struct thread_info *cti(void);
#endif

static inline struct thread_info *cti(void)
{
 struct thread_info **ti;
 __asm__("mr %0,13" : "=r"(ti));
 return *ti;
}
int fn()
{
 int ret = 0;

 cti()->preempt_count++;

 ret = cti()->preempt_count++;

 return ret;
}



mostrows@heater:~/tools.k42/powerpc/partDeb/os$ powerpc64-linux-g++    -
c   -o workqueue.o wq.C -O1 
mostrows@heater:~/tools.k42/powerpc/partDeb/os$ powerpc64-linux-objdump
-d workqueue.o 

workqueue.o:     file format elf64-powerpc

Disassembly of section .text:

0000000000000000 <._Z2fnv>:
   0:   7d aa 6b 78     mr      r10,r13
   4:   e9 6a 00 00     ld      r11,0(r10)
   8:   81 2b 00 00     lwz     r9,0(r11)
   c:   39 29 00 01     addi    r9,r9,1
  10:   91 2b 00 00     stw     r9,0(r11)
  14:   e9 6a 00 00     ld      r11,0(r10)
  18:   81 2b 00 00     lwz     r9,0(r11)
  1c:   7d 23 07 b4     extsw   r3,r9
  20:   39 29 00 01     addi    r9,r9,1
  24:   91 2b 00 00     stw     r9,0(r11)
  28:   4e 80 00 20     blr
  2c:   00 00 00 00     .long 0x0
  30:   00 09 00 00     .long 0x90000
  34:   00 00 00 00     .long 0x0
mostrows@heater:~/tools.k42/powerpc/partDeb/os$ powerpc64-linux-g++    -
c   -o workqueue.o wq.C -O1 -DBUG
mostrows@heater:~/tools.k42/powerpc/partDeb/os$ powerpc64-linux-objdump
-d workqueue.o 

workqueue.o:     file format elf64-powerpc

Disassembly of section .text:

0000000000000000 <._Z2fnv>:
   0:   48 00 00 00     b       0 <._Z2fnv>
   4:   00 00 00 00     .long 0x0
   8:   00 09 00 00     .long 0x90000
   c:   00 00 00 00     .long 0x0





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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17972