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Re: operator new returns nonzero

On Sat, 7 Sep 2013, Mike Stump wrote:

On Sep 7, 2013, at 3:33 AM, Marc Glisse <> wrote:
this patch teaches the compiler that operator new, when it can throw, isn't allowed to return a null pointer.

You sure:

@item -fcheck-new
@opindex fcheck-new
Check that the pointer returned by @code{operator new} is non-null
before attempting to modify the storage allocated.  This check is
normally unnecessary because the C++ standard specifies that
@code{operator new} only returns @code{0} if it is declared
@samp{throw()}, in which case the compiler always checks the
return value even without this option.  In all other cases, when
@code{operator new} has a non-empty exception specification, memory
exhaustion is signalled by throwing @code{std::bad_alloc}.  See also
@samp{new (nothrow)}.


Thanks, I didn't know that option. But it doesn't do the same. -fcheck-new is about the front-end inserting a test !=0 between malloc and the constructor. My patch is about teaching the middle-end that the value is not zero (so even user-coded comparisons with 0 can be simplified).

Now flag_check_new should probably disable this optimization... The 3 -fcheck-new testcases in the testsuite probably only pass because they don't have -O2.

Marc Glisse

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