Add a function to check whether a ValueRef is a constant

src/librustc/middle/trans/common.rs

@@ -850,6 +850,12 @@ pub fn const_get_elt(cx: &CrateContext, v: ValueRef, us: &[c_uint])
     }
 }
 
+pub fn is_const(v: ValueRef) -> bool {
+    unsafe {
+        llvm::LLVMIsConstant(v) == True
+    }
+}
+
 pub fn const_to_int(v: ValueRef) -> c_longlong {
     unsafe {
         llvm::LLVMConstIntGetSExtValue(v)