On 05/07/2016 11:38 AM, Andrew Haley wrote:
On 06/05/16 07:35, David Wohlferd wrote:
1) I'm not clear precisely what problem this patch fixes. It's true
that some people have incorrectly assumed that basic asm clobbers
memory and this change would fix their code. But some people also
incorrectly assume it clobbers registers. I assume that's why Jeff
Law proposed making basic asm "an opaque blob that
read/write/clobber any register or memory location."
A few more things:
Jeff Law did propose this, but it's impossible to do because it
inevitably causes reload failures.
Right.
My argument in support of Bernd's proposal is that it makes sense from
a *practical* software reliability point of view. It wouldn't hurt,
and might fix some significant bugs. It's similar to the targets
which always implicitly clobber "cc". It corresponds to what I always
assumed basic asm did, and I'm sure that I'm not alone. This change
might fix some real bugs and it is extremely unlikely to break
anything.
And by making basic asms use/clobber memory in particular, it means code
using them is less likely to break as the optimizers continue to get
smarter about memory loads/stores.
I haven't gone through the actual patch yet, but I like it's basic goals.
Jeff
