Merge pull request #11629 from JuliaLang/sk/shifts

<<, >>, >>>: use intrinsics for more mixed-type shift operations.

base/int.jl

@@ -104,6 +104,18 @@ for T in IntTypes
     else
         @eval >>(x::$T, y::Int) = box($T,ashr_int(unbox($T,x),unbox(Int,y)))
     end
+    for S in IntTypes
+        (S === Int128 || S === UInt128) && continue
+        @eval begin
+            <<(x::$T,  y::$S) = box($T, shl_int(unbox($T,x),unbox($S,y)))
+            >>>(x::$T, y::$S) = box($T,lshr_int(unbox($T,x),unbox($S,y)))
+        end
+        if issubtype(T,Unsigned)
+            @eval >>(x::$T, y::$S) = box($T,lshr_int(unbox($T,x),unbox($S,y)))
+        else
+            @eval >>(x::$T, y::$S) = box($T,ashr_int(unbox($T,x),unbox($S,y)))
+        end
+    end
 end
 
 bswap(x::Int8)    = x

base/operators.jl

@@ -112,9 +112,9 @@ const .≠ = .!=
 <<(x,y::Int)  = no_op_err("<<", typeof(x))
 >>(x,y::Int)  = no_op_err(">>", typeof(x))
 >>>(x,y::Int) = no_op_err(">>>", typeof(x))
-<<(x,y::Integer)  = x << convert(Int,y)
->>(x,y::Integer)  = x >> convert(Int,y)
->>>(x,y::Integer) = x >>> convert(Int,y)
+<<(x,y::Integer)  = typemax(Int) < y ? zero(x) : x <<  (y % Int)
+>>(x,y::Integer)  = typemax(Int) < y ? zero(x) : x >>  (y % Int)
+>>>(x,y::Integer) = typemax(Int) < y ? zero(x) : x >>> (y % Int)
 
 # fallback div, fld, and cld implementations
 # NOTE: C89 fmod() and x87 FPREM implicitly provide truncating float division,