On Jan 27, 2009, at 5:10 PM, Ian Lance Taylor wrote:
Chris Lattner <clatt...@apple.com> writes:
On Jan 27, 2009, at 1:10 PM, Ian Lance Taylor wrote:
Laurent GUERBY <laur...@guerby.net> writes:
Just curious: is there a "portable" way to read from memory
address zero in C code? "portable" here means likely to work
on most compilers without exotic compile flags in 2009.
char *my_null_pointer;
char fn() { return *my_null_pointer; }
It will be quite a while before whole program optimization is good
enough to prove that my_null_pointer is not referenced by anything
else.
Perhaps in GCC, but this is not a good solution if you care about
other compilers.
Is LLVM smart enough to optimize that away, even when using shared
libraries?
Yes absolutely. Just build with -fvisibility-hidden or use an export
map to say that my_null_pointer is not exported. If it is static, it
will also do it at -O2. This is not even a particularly aggressive
optimization.
-Chris
