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Description of problem:
GCC optimization at level -O1 or higher hides a NULL-dereference bug in an 'if' statement.

Version-Release number of selected component (if applicable):
gcc-4.4.5-6.el6.x86_64 and gcc-4.6.2-1.fc16.x86_64

How reproducible:
Every time.

Steps to Reproduce:
1. Compile the attached sample program with -O1, -O2 or -O3
  
Actual results:
Program runs to completion, returning success.

Expected results:
Program should crash due to a segmentation fault attempting to dereference 'ptr' in the IF statement.


Additional info:
If the attached program is built with -O0, the crash does not occur (and may hang around to cause unrelated issues later that are more difficult to track down).

Created attachment 534210 [details]
Sample program demonstrating the issue

That is fine, dereferencing a NULL pointer results in undefined behavior, when you reach such a statement the program can do anything, format your disk, segfault, anything else, and the compiler may optimize based on the assumption that it doesn't happen.