[LLVMbugs] [Bug 9481] New: Bad loop idiom memset transform

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=9481

           Summary: Bad loop idiom memset transform
           Product: new-bugs
           Version: unspecified
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: sharparrow1 at yahoo.com
                CC: llvmbugs at cs.uiuc.edu


a.c:
void bar();
int foo() {
  char a[10];
  int i;
  for (i = 0; i < 1000000; i++) {
    bar();
    a[i] = 23;
  }
  for (i = 1; i < 1000000; i++) {
    bar();
    a[i] += a[i-1];
  }
  return a[2]+a[6];
}

b.c:
#include <stdlib.h>
#include <stdio.h>
int foo();
void bar() { exit(0); }
int main() {
  foo();
}

$ clang a.c b.c -O2
$ ./a.out
Segmentation fault


The issue here is that a million element memset is inserted before the first
loop, when clearly the array does not contain that many elements.  Issue found
by inspection.

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