rustc: put range asserts on char loads.

A `char` is a Unicode codepoint, and so ranges from 0--0x10FFFF (with
the surrogate gaps): we may as well inform LLVM of this.

Author: huonw

src/librustc/middle/trans/datum.rs

@@ -546,6 +546,10 @@ fn load<'a>(bcx: &'a Block<'a>, llptr: ValueRef, ty: ty::t) -> ValueRef {
         C_undef(type_of::type_of(bcx.ccx(), ty))
     } else if ty::type_is_bool(ty) {
         LoadRangeAssert(bcx, llptr, 0, 2, lib::llvm::True)
+    } else if ty::type_is_char(ty) {
+        // a char is a unicode codepoint, and so takes values from 0
+        // to 0x10FFFF inclusive only.
+        LoadRangeAssert(bcx, llptr, 0, 0x10FFFF + 1, lib::llvm::False)
     } else {
         Load(bcx, llptr)
     }