On 10/14/2015 03:19 AM, Richard Biener wrote:
On Tue, Oct 13, 2015 at 10:59 PM, Richard Henderson <r...@redhat.com> wrote:
On 10/14/2015 02:49 AM, Jeff Law wrote:
The problem here is we don't know what address space the *0 is going to
hit,
right?
Correct, not before we do the walk of stmt to see what's present.
Isn't that also an issue for code generation as well?
What sort of problem are you thinking of? I haven't seen one yet.
The actual dereference of course has a properly address-space qualified zero.
OK. That's the bit I was missing and hinted out in the message I just
sent -- the address-space information is carried outside the address.
It seems that we're carrying it in the type, which is probably sensible
at some level.
Only your walking depends on operand_equal_p to treat different address-space
zero addresses as equal (which they are of course not ...):
And that's the key problem with carrying the address-space information
outside the address. We have to look at more than just the raw address
to determine if we've got a faulting *0 vs an address space qualified *0.
int
operand_equal_p (const_tree arg0, const_tree arg1, unsigned int flags)
{
...
/* Check equality of integer constants before bailing out due to
precision differences. */
if (TREE_CODE (arg0) == INTEGER_CST && TREE_CODE (arg1) == INTEGER_CST)
{
/* Address of INTEGER_CST is not defined; check that we did not forget
to drop the OEP_ADDRESS_OF/OEP_CONSTANT_ADDRESS_OF flags. */
gcc_checking_assert (!(flags
& (OEP_ADDRESS_OF | OEP_CONSTANT_ADDRESS_OF)));
return tree_int_cst_equal (arg0, arg1);
}
but only later we do
/* We cannot consider pointers to different address space equal. */
if (POINTER_TYPE_P (TREE_TYPE (arg0))
&& POINTER_TYPE_P (TREE_TYPE (arg1))
&& (TYPE_ADDR_SPACE (TREE_TYPE (TREE_TYPE (arg0)))
!= TYPE_ADDR_SPACE (TREE_TYPE (TREE_TYPE (arg1)))))
return 0;
So "fixing" that would make the walker only look for default
address-space zero dereferences.
Agreed.
I think we need to fix operand_equal_p anyway because 0 is clearly not
equal to 0 (only if they convert to the same literal)
My worry here is we'd be getting onto a slippery slope. But it may be
unavoidable.
jeff
