Warning for sampsyo#341

bril-rs/brillvm/README.md

@@ -9,7 +9,8 @@ be updated as Inkwell gets new support, within the constraints of the rust compi
 
 ## Runtime
 
-You must have a linkable runtime library available in the LLVM bc format. You can get this by calling `make rt`
+You must have a linkable runtime library available in the LLVM bc format.
+You can get this by calling `make rt`.
 
 ## Usage
 
@@ -38,6 +39,12 @@ the LLVM `mem2reg` pass will be sufficient if that is needed) but if you choose
 to supply Bril code with `phi` operations, Brillvm will assume that they follow
 LLVM's additional constraints.
 
+### Limitations
+
+- Rust and Bril both allow variables to be re-declared with different types. Brillvm
+  does not yet support this and assumes that a given variable will only have one
+  type within a function.
+
 ## TroubleShooting
 
 ### Floating Point values

bril-rs/brillvm/src/llvm.rs

@@ -96,10 +96,15 @@ impl<'a, 'b> Heap<'a, 'b> {
         name: &'b String,
         ty: &Type,
     ) -> WrappedPointer<'a> {
-        self.map
+        let result = self.map
             .entry(name)
             .or_insert_with(|| WrappedPointer::new(builder, context, name, ty))
-            .clone()
+            .clone();
+        if result.ty != *ty {
+            println!("`{}` had type `{}` but is now being assigned type `{}`", name, result.ty, ty);
+            unimplemented!("brillvm does not currently support variables within a function having different types. Implementing this might require a control flow analysis? Feel free to try and implement this.")
+        }
+        result
     }
 
     fn get(&self, name: &String) -> WrappedPointer<'a> {