[cfe-commits] [PATCH] Allow inline assembly to inherit readnone/readonly attributes from parent function
mcrosier at apple.com
Wed May 2 14:41:14 PDT 2012
On May 2, 2012, at 2:29 PM, Eric Christopher wrote:
> On May 2, 2012, at 2:23 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
>> On Wed, May 2, 2012 at 2:07 PM, Chad Rosier <mcrosier at apple.com> wrote:
>>> The attached patch allows inline assembly to inherit the readnone/readonly function attribute from the caller. This allows the attributes to be retained after function inlining. In turn, CSE is able to do it's magic on inline assembly statements.
>>> An orthogonal solution would be to add support for the const keyword for inline assembly (e.g., asm const("mov $0x12345678, %0" : "=r" (ptr)); ).
>> It's not obvious to me that this is safe... __attribute((const)) means
>> that a function doesn't cause expose any side-effects, not that it
>> doesn't have any internal state.
> Perhaps a way to give a statement an attribute then?
I think this is what I proposed as the orthogonal approach. However, assuming what Eli suggest below is correct, then this is not necessary. We can detect constness.
>> Note that there's another way we can compute readnone for the given
>> inline asm: an inline asm can be marked readnone if it doesn't have
>> any memory operands, isn't volatile, and doesn't clobber memory.
> In this case it's a read from memory so it'd be readonly... but the point is good.
More information about the cfe-commits