[cfe-commits] [PATCH] Allow inline assembly to inherit readnone/readonly attributes from parent function

[Eli Friedman]

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.

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.

-Eli