JDK 9 build with GCC 6.1.1

[David Holmes]

On 27/06/2016 9:45 PM, Andrew Haley wrote:
> On 27/06/16 12:32, David Holmes wrote:
>> I wasn't aware that we have any reliance on gcc doing any kind of "null
>> pointer check" ??
>
> Ah, right, I assumed you'd seen this before.
>
> If GCC sees something like
>
>    a->foo();
>    if (a) {
>      b();
>    }
>
> it will turn it into
>
>    a->foo();
>    b();
>
> This surprises some people, but is quite legal.

Okay. So I know I was initially surprised we have code that can do:

a->foo();

when a is NULL, but that is because it is actually compiled as:

foo(a);

IIRC foo() has a "if (this != NULL)" check internally.

I'm kind of surprised that the compiler itself seems to think a->foo()  
implies a is not NULL.

I also hope it either is extremely smart about this or else very  
conservative. Would want it to make a mess of this:

if (init(&a) != NULL) {
   a->foo();
}
else {
   log(...);
}
if (a)
   a->bar();

Cheers,
David

> Andrew.
>
>