[CCall] Don't ZExt half

Author: vchuravy

src/ccall.cpp

@@ -1053,7 +1053,7 @@ std::string generate_func_sig(const char *fname)
                 // see pull req #978. need to annotate signext/zeroext for
                 // small integer arguments.
                 jl_datatype_t *bt = (jl_datatype_t*)tti;
-                if (jl_datatype_size(bt) < 4) {
+                if (jl_datatype_size(bt) < 4 && bt != jl_float16_type) {
                     if (jl_signed_type && jl_subtype(tti, (jl_value_t*)jl_signed_type))
                         ab.addAttribute(Attribute::SExt);
                     else

test/llvmpasses/llvmcall.jl

@@ -13,7 +13,7 @@ end
 @generated foo(x)=:(ccall("extern foo", llvmcall, $x, ($x,), x))
 bar(x) = ntuple(i -> VecElement{Float16}(x[i]), 2)
 
-# CHECK: call half @foo(half zeroext %{{[0-9]+}})
+# CHECK: call half @foo(half %{{[0-9]+}})
 emit(foo, Float16)
 
 # CHECK: call [2 x half] @foo([2 x half] %{{[0-9]+}})