- Implement AST-to-HIR conversion of discard instructions.

- Handle constant expressions of (matrix {+,-,*,/} scalar)

- Handle constant expressions of (vector {+,-,*,/} scalar)

- Handle constant expressions of (matrix * vector)

- Handle constant expressions of (matrix * matrix)

- Handle currently unsupported constant expression types
  - ir_unop_sign
  - ir_unop_exp2
  - ir_unop_log2
  - ir_unop_u2f
  - ir_unop_trunc
  - ir_unop_ceil
  - ir_unop_floor
  - ir_unop_sin
  - ir_unop_cos
  - ir_binop_dot
  - ir_binop_min
  - ir_binop_max
  - ir_binop_pow

- Handle constant expressions of (struct == struct)

- Handle constant expressions of (struct != struct)

- Add support to ir_constant for array constants Arrays can only be
  - declared 'const' in GLSL 1.20+.  This is because there are no
    array constructors in GLSL 1.10, and any variable declared as
    'const' must have an initializer.

- Handle constant expressions of (array == array)

- Handle constant expressions of (array != array)

- Treat built-in functions with constant parameters as constant expressions.
  - Rewrite all built-in functions return a single expression.
  - Modify the HIR generator for functions to automatically inline built-in
    functions durning translation.
  - Care must be taken to handle both the 1.10 rules and the 1.20+ rules.  In
    1.10, built-in functions cannot be constant expressions.

- Detect non-void functions that lack a return statement

- Detect return statements with a type not matching the funciton's
  return type.

- Handle over-riding built-in functions
  - Is the overload per-compilation unit or per-linked shader?

- Handle redeclaration of built-in variables
  - Handle addition of qualifiers such as 'invariant' or 'centroid'.
  - Handle resizing of arrays.
  - Other?  We'll have to look at the spec.

1.30 features:

- Implement AST-to-HIR conversion of bit-shift operators.

- Implement AST-to-HIR conversion of bit-wise {&,|,^,!} operators.

- Implement AST-to-HIR conversion of switch-statements
  - switch
  - case
  - Update break to correcly handle mixed nexting of switch-statements
    and loops.

- Handle currently unsupported constant expression types
  - ir_unop_bit_not
  - ir_binop_mod
  - ir_binop_lshift
  - ir_binop_rshift
  - ir_binop_bit_and
  - ir_binop_bit_xor
  - ir_binop_bit_or