do not assume anything about the top bits in llvm intrinsics receiving i8/i16 values - while normally we can assume that the top bits are clear due to how LLVM creates the call, if the call is an ffi or constructed in a non-clang way (see rust-lang/rust#39119) then we must be careful

Author: kripken

src/library.js

@@ -951,15 +951,15 @@ LibraryManager.library = {
   llvm_ctlz_i8: function(x, isZeroUndef) {
     x = x | 0;
     isZeroUndef = isZeroUndef | 0;
-    return (Math_clz32(x) | 0) - 24 | 0;
+    return (Math_clz32(x & 0xff) | 0) - 24 | 0;
   },
 
   llvm_ctlz_i16__asm: true,
   llvm_ctlz_i16__sig: 'ii',
   llvm_ctlz_i16: function(x, isZeroUndef) {
     x = x | 0;
     isZeroUndef = isZeroUndef | 0;
-    return (Math_clz32(x) | 0) - 16 | 0
+    return (Math_clz32(x & 0xffff) | 0) - 16 | 0
   },
 
   llvm_ctlz_i64__asm: true,