[LLVMbugs] [Bug 2791] New: possible induction variable bug

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=2791

           Summary: possible induction variable bug
           Product: new-bugs
           Version: unspecified
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: regehr at cs.utah.edu
                CC: llvmbugs at cs.uiuc.edu


Seen using r56177 on Ubuntu Hardy on ia32.

The -O3 result is clearly wrong.  Notice that g_5 is not assigned to anywhere
except in the header of the for loop.

llvm-gcc is valgrind-clean on the -O3 run.

regehr at john-home:~/volatile/tmp31$ llvm-gcc -O1 -w small.c -o small 
regehr at john-home:~/volatile/tmp31$ ./small
2
regehr at john-home:~/volatile/tmp31$ llvm-gcc -O3 -w small.c -o small 
regehr at john-home:~/volatile/tmp31$ ./small
1
regehr at john-home:~/volatile/tmp31$ cat small.c

#include <stdint.h>
#include <limits.h>
#include <stdio.h>

static inline unsigned long int
mod_rhs(const long int rhs)
{
    if (rhs == 0) return 1;
    return rhs;
}

static inline int
rshift_s_s(int left, int right)
{
        if ((left < 0)
                || (right < 0)
                || (right >= sizeof(int)*CHAR_BIT)) {
                /* Avoid implementation-defined and undefined behavior. */
                return left;
        }
        return left >> right;
}

static inline unsigned int
lshift_u_u(unsigned int left, unsigned int right)
{
        if ((right >= sizeof(unsigned int)*CHAR_BIT)
                || (left > (UINT_MAX >> right))) {
                /* Avoid undefined behavior. */
                return left;
        }
        return left << right;
}

static inline int
lshift_s_s(int left, int right)
{
        if ((left < 0)
                || (right < 0)
                || (right >= sizeof(int)*CHAR_BIT)
                || (left > (INT_MAX >> right))) {
                /* Avoid undefined behavior. */
                return left;
        }
        return left << right;
}

uint32_t g_5;
uint32_t g_234;
uint32_t g_248;
volatile uint32_t g_283;
uint32_t g_286;
int32_t func_12 (uint32_t p_13, uint32_t p_14, uint32_t p_15);
int32_t
func_12 (uint32_t p_13, uint32_t p_14, uint32_t p_15)
{
  return 1;
}

int32_t func_50 (uint32_t p_51, int8_t p_53);
int32_t func_50 (uint32_t p_51, int8_t p_53)
{
  return 1;
}

int32_t func_55 (uint16_t p_57);
int32_t func_55 (uint16_t p_57)
{
  if (1 % mod_rhs (1))
    return 1;
  return 1;
}

int32_t func_95 (int8_t p_96);
int32_t func_95 (int8_t p_96)
{
  return 1;
}

int32_t func_103 (uint32_t p_105);
int32_t func_103 (uint32_t p_105)
{
  return 1;
}

void func_8 (void);
void func_8 (void)
{
  int32_t p_9 = 1;
  uint32_t l_11 = 0;
  uint32_t l_281;

  if (g_5) return;

  uint32_t l_280;
  uint32_t l_282 = 1;
  if (((rshift_s_s
        (g_5
         && 1, func_12 (1 & (l_280 * g_234), func_50 ((1 | l_11), l_281),
                        (l_11 > (g_283 && p_9))))) + (lshift_u_u (g_5,
                                                                  0)) ==
       1) + (func_55 (func_103 (&l_282) & g_248 +
                      (lshift_s_s ((lshift_u_u (g_286, 1)), func_95 (p_9)))) >
             ((lshift_u_u (p_9, 1)) % mod_rhs (1))))
    {
    }
  else
    for (1; p_9; p_9--)
      {
      }
}

void func_1 (void);
void func_1 (void)
{
  for (g_5 = 0; g_5 <= 1; g_5++) {
    func_8 ();
  }
}

int
main (void)
{
  func_1 ();
  printf ("%d\n", g_5);
  return 0;
}


-- 
Configure bugmail: http://llvm.org/bugs/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.