RFR: 8240302: x64: Assembler::reachable redundantly call Relocation::type() more than once

[Ioi Lam]

Looks good to me, too.

I was wondering if the C compiler would be a little smarter if 
Relocation::type() was declared as a const function, like:

- virtual relocInfo::relocType type()       { return relocInfo::none; }
+ virtual relocInfo::relocType type() const { return relocInfo::none; }

But apparently GCC will not elide the multiple calls:

// test.cpp
class X {
public: virtual int get() const { return 1; }
};

class Y : public X {
public:  virtual int get() const { return 2; }
};

X* xx = 0;
int testfunc(char* argv[]) {
   X* x = xx;
   return x->get() + x->get() + x->get();
}

$ gcc -O -S -o - test.cpp | grep call
     call    *(%rax)
     call    *(%rax)
     call    *(%rax)

So it looks like we must manually save the return value of type() as 
done in your patch.

Thanks
- Ioi

On 3/2/20 4:11 PM, Vladimir Kozlov wrote:
> Good cleanup.
>
> Thanks,
> Vladimir
>
> On 3/2/20 7:07 AM, Claes Redestad wrote:
>> Hi,
>>
>> in the x64-version Assembler::reachable method, various calls to
>> adr.reloc() are not hoisted by the compiler, due calling into the
>> virtual method Relocation::type(). This means each call to reachable
>> typically do several redundant calls into Relocation::type()
>>
>> This patch refactors all these calls into a single one, which has a
>> small, but measurable, effect on startup (and likely some small
>> effect on JIT compiler throughput in general)
>>
>> Webrev: http://cr.openjdk.java.net/~redestad/8240302/open.00/
>> Bug:    https://bugs.openjdk.java.net/browse/JDK-8240302
>>
>> Testing: tier1-3
>>
>> Thanks!
>>
>> /Claes