fuzzgen: Add stack map variables

cranelift/fuzzgen/src/function_generator.rs

@@ -1879,19 +1879,26 @@ where
             .iter()
             .map(|param| param.value_type)
             .zip(builder.block_params(block).iter().copied())
-            .collect();
+            .map(|(ty, param)| Ok((ty, param, self.u.arbitrary()?)))
+            .collect::<Result<Vec<_>>>()?;
 
         // Create a pool of vars that are going to be used in this function
         for _ in 0..self.param(&self.config.vars_per_function)? {
             let ty = self.u._type((&*self.isa).supports_simd())?;
             let value = self.generate_const(builder, ty)?;
-            vars.push((ty, value));
+            let uses_stack_map = self.u.arbitrary()?;
+            vars.push((ty, value, uses_stack_map));
         }
 
-        for (id, (ty, value)) in vars.into_iter().enumerate() {
+        for (id, (ty, value, uses_stack_map)) in vars.into_iter().enumerate() {
             let var = Variable::new(id);
             builder.declare_var(var, ty);
             builder.def_var(var, value);
+
+            if uses_stack_map {
+                builder.declare_var_needs_stack_map(var);
+            }
+
             self.resources
                 .vars
                 .entry(ty)