remove switch_ty reliance in codegen

Author: RalfJung

src/librustc_codegen_ssa/mir/block.rs

@@ -200,6 +200,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         targets: &Vec<mir::BasicBlock>,
     ) {
         let discr = self.codegen_operand(&mut bx, &discr);
+        // `switch_ty` is redundant, sanity-check that.
+        assert_eq!(discr.layout.ty, switch_ty);
         if targets.len() == 2 {
             // If there are two targets, emit br instead of switch
             let lltrue = helper.llblock(self, targets[0]);

src/librustc_middle/mir/mod.rs

@@ -1075,6 +1075,8 @@ pub enum TerminatorKind<'tcx> {
         discr: Operand<'tcx>,
 
         /// The type of value being tested.
+        /// This is always the same as the type of `discr`.
+        /// FIXME: remove this redundant information. Currently, it is relied on by pretty-printing.
         switch_ty: Ty<'tcx>,
 
         /// Possible values. The locations to branch to in each case

src/librustc_mir/interpret/terminator.rs

@@ -24,9 +24,10 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
             Goto { target } => self.go_to_block(target),
 
-            SwitchInt { ref discr, ref values, ref targets, .. } => {
+            SwitchInt { ref discr, ref values, ref targets, switch_ty } => {
                 let discr = self.read_immediate(self.eval_operand(discr, None)?)?;
                 trace!("SwitchInt({:?})", *discr);
+                assert_eq!(discr.layout.ty, switch_ty);
 
                 // Branch to the `otherwise` case by default, if no match is found.
                 assert!(!targets.is_empty());
@@ -55,7 +56,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 ref args,
                 destination,
                 ref cleanup,
-                from_hir_call: _from_hir_call,
+                from_hir_call: _,
                 fn_span: _,
             } => {
                 let old_stack = self.frame_idx();