[PATCH] D19061: [ARM] Add support for the X asm constraint

[Renato Golin via llvm-commits]

rengolin added a comment.

Do'h! I missed the PR reference, my apologies.

Though, wrt the blog post, I think it's a very lean source for such a generic case like this. I suggest you try to use the constraint on GCC and come up with a general description for its behaviour, what's allowed and what's not. Maybe even talk to a few GCC engineers once you have a better idea, and then be able to accurately describe what we want to implement.

Without that, it'll be hard to review the patch, and adding a hack to make your specific use case pass wouldn't be very constructive, either. :)

cheers,
--renato


================
Comment at: lib/Target/ARM/ARMISelLowering.cpp:11457
@@ +11456,3 @@
+      ConstraintVT.getSizeInBits() == 128))
+    return "w";
+
----------------
sbaranga wrote:
> rengolin wrote:
> > No "t" for 32-bit FP registers?
> Why "t" (wouldn't "w" be enough)? 
"t" would select an S register, while "w" would select a D reg.

If this is "anything", shouldn't it also allow immediate values and expressions?


http://reviews.llvm.org/D19061