RE: ctor unnecessarily wiping of PODs

["Hite, Christopher" <Christopher dot Hite at partner dot commerzbank dot com>]

Hi,

I think I've got an optimizer bug producing a bzero of data that doesn't need initialization.

Whether Ray has a ctor defined or not gcc wipes the memory 257 words for no reason.  What does have an effect is if you call the ctor of just  Ray it doesn't clear the data.

One would expect none of the PODs to be inited unless explicitly done so in the code

I'm guessing there's some kind of a bzero optimization where padding and non-inited PODs can be cleared along with several fields that need to be.  I'm guessing that this optimization is broken somehow.

I'm getting this on gcc 4.6.0 debug and O3.

struct Ray{
	unsigned n;g
	int u[0x100];
	//Ray() : n() {}
};

struct Ray2: Ray {};

void makeRay(void*v){
	new(v)Ray2();
}

g++  -ftemplate-depth-512 -O3 -finline-functions -Wno-inline -Wall -pthread -m32 -g -march=core2

00006ca0 <makeRay(void*)>:
    6ca0:       57                      push   %edi
    6ca1:       8b 54 24 08             mov    0x8(%esp),%edx
    6ca5:       85 d2                   test   %edx,%edx
    6ca7:       74 0b                   je     6cb4 <makeRay(void*)+0x14>
    6ca9:       b9 33 00 00 00          mov    $0x33,%ecx
    6cae:       31 c0                   xor    %eax,%eax
    6cb0:       89 d7                   mov    %edx,%edi
    6cb2:       f3 ab                   rep stos %eax,%es:(%edi)
    6cb4:       5f                      pop    %edi
    6cb5:       c3                      ret

Chris