Re:Xcode 4 ships a buggy compiler
by comex on Saturday December 31, 2011 @12:22AM
(#3410231)
> instead, alloca(0) behaves as if it returns NULL in some cases, and non-NULL in other cases, which is completely allowed.
Not really. I can't reproduce the optimizer bug here (on the contrary, the optimizer in the version of llvm-gcc I have installed seems to assume it is null[1]), but if alloca() is returning null and the optimizer assumes it's non-null, the value will be treated as non-null in the function but null if, say, the value is passed into a non-inline function which compares it to null.
[1] i686-apple-darwin11-llvm-gcc-4.2 (GCC) 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.1.00)
Not really. I can't reproduce the optimizer bug here (on the contrary, the optimizer in the version of llvm-gcc I have installed seems to assume it is null[1]), but if alloca() is returning null and the optimizer assumes it's non-null, the value will be treated as non-null in the function but null if, say, the value is passed into a non-inline function which compares it to null.
[1] i686-apple-darwin11-llvm-gcc-4.2 (GCC) 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.1.00)