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Re: GCC 4.4/4.6/4.7 uninitialized warning regression?
On Wed, Apr 20, 2011 at 9:06 PM, Xinliang David Li <email@example.com> wrote:
> On Wed, Apr 20, 2011 at 12:03 PM, Cary Coutant <firstname.lastname@example.org> wrote:
>>> This brings out 2 questions. ?Why don't GCC 4.4/4.6/4.7 warn it?
>>> Why doesn't 64bit GCC 4.2 warn it?
>> Good question. It seems that the difference is whether the compiler
>> generates a field-by-field copy or a call to memcpy(). According to
>> David, the trunk gcc in 32-bit mode doesn't call memcpy, but still
>> doesn't warn. He's looking at it.
> It seems to be related to alias rewrite -- the use of single memory
> token somehow blocks the warning (even though the struct read are
The warning never really worked by design. It worked by luck if
a read used the default definition of a non-aliased VOP. Which made
it work for simple testcases but almost never for real code.
A real uninitialized warning for memory wouldn't be difficult to write
using the alias walking machinery (just use walk_aliased_vdefs,
stop on the first callback assuming that's an initialization, warn
if you don't get any callback). It's just going to be expensive.