Merge pull request #340 from uwplse/oflatt-upstream-rs2bril-init

[rs2bril] Array initialization using Bril loop instead of unrolling

bril-rs/rs2bril/README.md

@@ -12,8 +12,9 @@ View the interface with `cargo doc --open` or install with `make install` using
 - Automatic static memory management <https://www.cs.cornell.edu/courses/cs6120/2020fa/blog/asmm/> has not been implemented so arrays must be explicitly dropped where `drop` is specialized to translate to a call to free: `drop([0]);`
 - For loops, `continue`, `break`, and ranges have not been implemented(but could be).
 - Memory is implemented using Rust arrays. These are statically sized values unlike how calls to Bril `alloc` can be dynamically sized. One solution is to just allocate a large enough array and then treat the dynamic size like the length. (A subset of vectors could also be specialized in the future).
+- Arrays must be initialized with repetition syntax, which is awkward for nested arrays.
 - In normal Rust, `if` can also be used as an expression that evaluates a value to be put in a variable. This is not implemented and it is assumed that there will only be if statements.
-- The Bril code that it produces is super inefficient and it is left to other tools to optimize it. Array initialization is unrolled is not an optimal solution.
+- The Bril code that it produces is super inefficient and it is left to other tools to optimize it.
 - `!=` and automatic promotions of integer literals to floats are not implemented.
-- to support indexing into arrays, you can cast to usize in the Rust code. This will be ignored when generating Bril. `arr[i as usize];`
-- The parts of Rust which make it valid like lifetimes, references, mutability, and function visibility are ignored and compiled away in Bril.
+- To support indexing into arrays, you can cast to usize in the Rust code. This will be ignored when generating Bril. `arr[i as usize];`
+- The parts of Rust which make it valid like lifetimes, references, mutability, and function visibility are ignored and compiled away in Bril.

bril-rs/rs2bril/src/lib.rs

@@ -393,6 +393,146 @@ fn from_signature_to_function(
     }
 }
 
+/// Create and initialize an array containing `num_rep` repetitions of `rep_var`.
+fn array_repetition_helper(
+    rep_var: &String,
+    num_reps: i64,
+    mut code: Vec<Code>,
+    state: &mut State,
+) -> (Option<String>, Vec<Code>) {
+    // make constant one
+    let one = state.fresh_var(Type::Int);
+    code.push(Code::Instruction(Instruction::Constant {
+        dest: one.clone(),
+        op: ConstOps::Const,
+        pos: None,
+        const_type: Type::Int,
+        value: Literal::Int(1),
+    }));
+
+    let arr_type = Type::Pointer(Box::new(state.get_type_for_ident(rep_var)));
+    let pointer = state.fresh_var(arr_type.clone());
+    let size = state.fresh_var(Type::Int);
+    code.push(Code::Instruction(Instruction::Constant {
+        dest: size.clone(),
+        op: ConstOps::Const,
+        pos: None,
+        const_type: Type::Int,
+        value: Literal::Int(num_reps),
+    }));
+    code.push(Code::Instruction(Instruction::Value {
+        args: vec![size.clone()],
+        dest: pointer.clone(),
+        funcs: Vec::new(),
+        labels: Vec::new(),
+        op: ValueOps::Alloc,
+        pos: None,
+        op_type: arr_type.clone(),
+    }));
+
+    // make an index pointer for the array
+    let current_ptr = state.fresh_var(arr_type.clone());
+    code.push(Code::Instruction(Instruction::Value {
+        args: vec![pointer.clone()],
+        dest: current_ptr.clone(),
+        funcs: Vec::new(),
+        labels: Vec::new(),
+        op: ValueOps::Id,
+        pos: None,
+        op_type: arr_type.clone(),
+    }));
+
+    let start_label = state.fresh_label();
+    let then_label = state.fresh_label();
+    let end_label = state.fresh_label();
+
+    let iter = state.fresh_var(Type::Int);
+    code.push(Code::Instruction(Instruction::Constant {
+        dest: iter.clone(),
+        op: ConstOps::Const,
+        pos: None,
+        const_type: Type::Int,
+        value: Literal::Int(0),
+    }));
+
+    code.push(Code::Label {
+        label: start_label.clone(),
+        pos: None,
+    });
+
+    // check if iter < size
+    let cond_var = state.fresh_var(Type::Bool);
+    code.push(Code::Instruction(Instruction::Value {
+        args: vec![iter.clone(), size],
+        dest: cond_var.clone(),
+        funcs: Vec::new(),
+        labels: Vec::new(),
+        op: ValueOps::Lt,
+        pos: None,
+        op_type: Type::Bool,
+    }));
+
+    code.push(Code::Instruction(Instruction::Effect {
+        args: vec![cond_var],
+        funcs: Vec::new(),
+        labels: vec![then_label.clone(), end_label.clone()],
+        op: EffectOps::Branch,
+        pos: None,
+    }));
+
+    code.push(Code::Label {
+        label: then_label,
+        pos: None,
+    });
+
+    // write var to the current ptr
+    code.push(Code::Instruction(Instruction::Effect {
+        args: vec![current_ptr.clone(), rep_var.clone()],
+        funcs: Vec::new(),
+        labels: Vec::new(),
+        op: EffectOps::Store,
+        pos: None,
+    }));
+
+    // increment current ptr
+    code.push(Code::Instruction(Instruction::Value {
+        args: vec![current_ptr.clone(), one.clone()],
+        dest: current_ptr,
+        funcs: Vec::new(),
+        labels: Vec::new(),
+        op: ValueOps::PtrAdd,
+        pos: None,
+        op_type: arr_type,
+    }));
+
+    // increment iter
+    code.push(Code::Instruction(Instruction::Value {
+        args: vec![iter.clone(), one],
+        dest: iter,
+        funcs: Vec::new(),
+        labels: Vec::new(),
+        op: ValueOps::Add,
+        pos: None,
+        op_type: Type::Int,
+    }));
+
+    // jump to start label
+    code.push(Code::Instruction(Instruction::Effect {
+        args: Vec::new(),
+        funcs: Vec::new(),
+        labels: vec![start_label],
+        op: EffectOps::Jump,
+        pos: None,
+    }));
+
+    code.push(Code::Label {
+        label: end_label,
+        pos: None,
+    });
+
+    (Some(pointer), code)
+}
+
 fn array_init_helper(
     vars: Vec<String>,
     mut code: Vec<Code>,
@@ -909,8 +1049,12 @@ fn from_expr_to_bril(expr: Expr, state: &mut State) -> (Option<String>, Vec<Code
                 _ => panic!("can't handle non-literal Int for repeated array length"),
             };
 
-            let vars = std::iter::repeat(var.unwrap()).take(array_len).collect();
-            array_init_helper(vars, code, state)
+            array_repetition_helper(
+                &var.unwrap(),
+                i64::try_from(array_len).unwrap(),
+                code,
+                state,
+            )
         }
         Expr::Return(ExprReturn {
             attrs,