Only remove arg_count() method

kani-compiler/src/kani_middle/transform/body.rs

@@ -17,10 +17,14 @@ pub struct MutableBody {
 
     /// Declarations of locals within the function.
     ///
-    /// The first local is the return value pointer, followed by locals for the function arguments,
-    /// followed by any user-declared variables and temporaries.
+    /// The first local is the return value pointer, followed by `arg_count`
+    /// locals for the function arguments, followed by any user-declared
+    /// variables and temporaries.
     locals: Vec<LocalDecl>,
 
+    /// The number of arguments this function takes.
+    arg_count: usize,
+
     /// Debug information pertaining to user variables, including captures.
     var_debug_info: Vec<VarDebugInfo>,
 
@@ -54,6 +58,7 @@ impl MutableBody {
     pub fn from(body: Body) -> Self {
         MutableBody {
             locals: body.locals().to_vec(),
+            arg_count: body.arg_locals().len(),
             spread_arg: body.spread_arg(),
             blocks: body.blocks,
             var_debug_info: body.var_debug_info,
@@ -63,7 +68,14 @@ impl MutableBody {
 
     /// Create the new body consuming this mutable body.
     pub fn into(self) -> Body {
-        Body::new(self.blocks, self.locals, self.var_debug_info, self.spread_arg, self.span)
+        Body::new(
+            self.blocks,
+            self.locals,
+            self.arg_count,
+            self.var_debug_info,
+            self.spread_arg,
+            self.span,
+        )
     }
 
     /// Add a new local to the body with the given attributes.