[PATCH] D49606: [ms] Add __shiftleft128 / __shiftright128 intrinsics

[Sanjay Patel via Phabricator via cfe-commits]

spatel added a comment.

In https://reviews.llvm.org/D49606#1170278, @craig.topper wrote:

> Here are the IR patterns for this that work. Not sure if we can do this directly in C, we need a 128 bit type, but maybe we can emit it from CGBuiltin.cpp?
>
>   define i64 @__shiftleft128(i64 %x, i64 %y, i8 %amt) {
>     %a = zext i64 %x to i128
>     %b = zext i64 %y to i128
>     %c = shl i128 %b, 64
>     %d = or i128 %a, %c
>     %amtmask = and i8 %amt, 63
>     %e = zext i8 %amtmask to i128
>     %f = shl i128 %d, %e
>     %g = lshr i128 %f, 64
>     %h = trunc i128 %g to i64
>     ret i64 %h
>   }
>  
>   define i64 @__shiftright128(i64 %x, i64 %y, i8 %amt) {
>     %a = zext i64 %x to i128
>     %b = zext i64 %y to i128
>     %c = shl i128 %b, 64
>     %d = or i128 %a, %c
>     %amtmask = and i8 %amt, 63
>     %e = zext i8 %amtmask to i128
>     %f = lshr i128 %d, %e
>     %g = trunc i128 %f to i64
>     ret i64 %g
>   }
>


I’m not at my dev machine, but this is exactly the definition of funnel shift, no? Unless that got reverted, adding/modifying clang builtins was the next step in the plan for those intrinsics. We probably need some backend work to match the variable shift version, but shift-by constant should already work.


https://reviews.llvm.org/D49606