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Re: Null pointer check elimination
Gabriel Dos Reis wrote:
"Michael N. Moran" <mike@mnmoran.org> writes:
| From info gcc:
|
| `-fdelete-null-pointer-checks'
| Use global dataflow analysis to identify and eliminate useless
| checks for null pointers. The compiler assumes that dereferencing
| a null pointer would have halted the program. If a pointer is
| checked after it has already been dereferenced, it cannot be null.
|
| The second sentence makes me question the difference between an
| actual dereferencing operation and the use of a dereferencing
| operator used to convert a pointer to a C++ reference. Clearly
| (to me anyway ;-) the conversion case does not actually cause
| an access to the object.
It is not a conversion. It is a dereference operation that is defined
only for non-null operand. No ifs, no buts.
I'm in over my head, but ... (oops there's a but ;-) here goes:
void bar(int& a);
void foo(int* a)
{
// dereference: conversion to reference
// Since there is not necessarily any object access,
// thus no assured SEGFAULT.
bar(*a);
// dereference: access to object
// If a is null, then SEGFAULT
*a = 0;
}
Sorry to drag this out. I'm sure its just one of those
"that's the way the language is defined Moran get over it"
issues, but (no ifs) ...
--
Michael N. Moran (h) 770 516 7918
5009 Old Field Ct. (c) 678 521 5460
Kennesaw, GA, USA 30144 http://mnmoran.org
"So often times it happens, that we live our lives in chains
and we never even know we have the key."
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