@Chris, I'm having trouble understanding your message. Do you mean
that you hope to implement this soon, or that you don't intend to?
@Félix, no, however I do think it would a good feature to have if you
need to optimize certain lines of code beyond preset optimizer passes.
···
On 12/3/16, Chris Lattner <clattner@apple.com> wrote:
On Dec 3, 2016, at 3:12 PM, Ethin Probst via swift-evolution >> <swift-evolution@swift.org> wrote:
Hello all,
My name is Ethin and I am new to this community. However, I certainly
am no newbie when it comes to software development, and have emailed
all of you to file a proposal of inline assembly in Swift. The
assembly language would be within an asm {...} block.Hi Ethin,
While it isn’t a pressing short term priority, I would like to see something
to address the needs served by inline assembly in Swift at some point. We
have a lot of experience from the Clang/C space to draw on here, and there
are three general approaches supported by Clang:1) “Processor Intrinsics" for instructions. Compilers for some
architectures provide this as the only option (Itanium in MSVC IIRC).
2) “Microsoft” or “CodeWarrior” style inline assembly, like you show. This
doesn’t require the developer to write register constraints, and sometimes
allows direct use of local variables in the asm block.
3) “GCC” style inline assembly, which requires the user to write register
constraints like “rmi”.I’m significantly opposed to ever supporting GCC-style assembly, since it is
very very common for developers to get the constraints wrong, and the
compiler knows the instruction set anyway.When it comes to #1 vs #2, there are tradeoffs:
#1 is simpler, doesn’t require language extensions (and can be done today by
a sufficiently motivated person), and composes better with
processor-independent intrinsics (like cross platform prefetch operations).#2 is better for folks who “think in assembly”, because it has a more
obvious and direct mapping to it. It has the additional downside of having
to deal with multiple dialects of assembly, e.g. AT&T vs Intel syntax.-Chris
--
Signed,
Ethin D. Probst