Conditional schedules

• Add if statements to the scheduling language.
• Add a feature(...) function that can be used to test for whether a feature is enabled
  • For this to work, the scheduler needs to be run from a Cargo build script since it relies on testing environment variables (as described here).
• Modified matmul to use a single schedule testing for the "cuda" feature

juno_scheduler/src/compile.rs

@@ -275,6 +275,35 @@ fn compile_stmt(
                 limit,
             }])
         }
+        parser::Stmt::IfThenElse {
+            span: _,
+            cond,
+            thn,
+            els,
+        } => {
+            let cond = compile_exp_as_expr(cond, lexer, macrostab, macros)?;
+
+            macros.open_scope();
+            let thn = ir::ScheduleStmt::Block {
+                body: compile_ops_as_block(*thn, lexer, macrostab, macros)?,
+            };
+            macros.close_scope();
+
+            macros.open_scope();
+            let els = match els {
+                Some(els) => ir::ScheduleStmt::Block {
+                    body: compile_ops_as_block(*els, lexer, macrostab, macros)?,
+                },
+                None => ir::ScheduleStmt::Block { body: vec![] },
+            };
+            macros.close_scope();
+
+            Ok(vec![ir::ScheduleStmt::IfThenElse {
+                cond,
+                thn: Box::new(thn),
+                els: Box::new(els),
+            }])
+        }
         parser::Stmt::MacroDecl { span: _, def } => {
             let parser::MacroDecl {
                 name,