[LLVMbugs] [Bug 2848] New: new volatile regression

bugzilla-daemon at cs.uiuc.edu bugzilla-daemon at cs.uiuc.edu
Wed Oct 1 19:42:37 PDT 2008


           Summary: new volatile regression
           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 on r56938 on Ubuntu Hardy on ia32.

This is a strange one: wrong code at -O0, correct at other optimization levels.

I don't think this problem was there 24 hours ago.

regehr at john-home:~/volatile/tmp50$ llvm-gcc -O0 small.c -S -o - | grep g_126
        .type   g_126, at object
        .section        .gnu.linkonce.b.g_126,"aw", at nobits
        .comm   g_126,4,4               # g_126

The x86 code contains no load from the volatile location!  The LLVM looks OK.

int mod_rhs (int x)
  return x;

volatile unsigned int g_126;

int func_93 (void);
int func_93 (void)
  return (g_126 > (mod_rhs (1)) < 0);

int main (void)
  func_93 ();
  return 0;

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