Implement select and vselect instructions.

This gives us the opportunity to use the AsBool derived type variables and a
Select instruction format with a non-default typevar_operand setting.

cranelift/docs/langref.rst

@@ -656,35 +656,12 @@ load a constant into an SSA value.
 .. autoinst:: f32const
 .. autoinst:: f64const
 .. autoinst:: vconst
-
-.. inst:: a = select c, x, y
-
-    Conditional select.
-
-    :arg b1 c: Controlling flag.
-    :arg T x: Value to return when ``c`` is true.
-    :arg T y: Value to return when ``c`` is false. Must be same type as ``x``.
-    :result T a: Same type as ``x`` and ``y``.
-
-    This instruction selects whole values. Use :inst:`vselect` for lane-wise
-    selection.
+.. autoinst:: select
 
 Vector operations
 -----------------
 
-.. inst:: a  = vselect c, x, y
-
-    Vector lane select.
-
-    Select lanes from ``x`` or ``y`` controlled by the lanes of the boolean
-    vector ``c``.
-
-    :arg b1xN c: Controlling flag vector.
-    :arg TxN x: Vector with lanes selected by the true lanes of ``c``.
-              Must be a vector type with the same number of lanes as ``c``.
-    :arg TxN y: Vector with lanes selected by the false lanes of ``c``.
-              Must be same type as ``x``.
-    :result TxN a: Same type as ``x`` and ``y``.
+.. autoinst:: vselect
 
 .. inst:: a = vbuild x, y, z, ...
 

cranelift/src/libcretonne/instructions.rs

@@ -158,6 +158,11 @@ pub enum InstructionData {
         second_result: Value,
         args: [Value; 2],
     },
+    Select {
+        opcode: Opcode,
+        ty: Type,
+        args: [Value; 3],
+    },
     Jump {
         opcode: Opcode,
         ty: Type,
@@ -295,13 +300,13 @@ impl InstructionData {
 ///
 /// Bits 4-7:
 ///     Permitted set of types for the controlling type variable as an index into `TYPE_SETS`.
-/// 
+///
 /// Bits 8-15:
 ///     Offset into `OPERAND_CONSTRAINT` table of the descriptors for this opcode. The first
 ///     `fixed_results()` entries describe the result constraints, then follows constraints for the
 ///     fixed `Value` input operands. The number of `Value` inputs isdetermined by the instruction
 ///     format.
-///   
+///
 #[derive(Clone, Copy)]
 pub struct OpcodeConstraints(u16);
 

cranelift/src/libcretonne/write.rs

@@ -156,6 +156,9 @@ pub fn write_instruction(w: &mut Write, func: &Function, inst: Inst) -> Result {
         BinaryImm { opcode, lhs, rhs, .. } => writeln!(w, "{} {}, {}", opcode, lhs, rhs),
         BinaryImmRev { opcode, lhs, rhs, .. } => writeln!(w, "{} {}, {}", opcode, lhs, rhs),
         BinaryOverflow { opcode, args, .. } => writeln!(w, "{} {}, {}", opcode, args[0], args[1]),
+        Select { opcode, args, .. } => {
+            writeln!(w, "{} {}, {}, {}", opcode, args[0], args[1], args[2])
+        }
         Jump { opcode, ref data, .. } => writeln!(w, "{} {}", opcode, data),
         Branch { opcode, ref data, .. } => writeln!(w, "{} {}", opcode, data),
         BranchTable { opcode, arg, table, .. } => writeln!(w, "{} {}, {}", opcode, arg, table),

cranelift/src/libreader/parser.rs

@@ -668,6 +668,7 @@ impl<'a> Parser<'a> {
                     args: [lhs, rhs],
                 }
             }
+            InstructionFormat::Select |
             InstructionFormat::Jump |
             InstructionFormat::Branch |
             InstructionFormat::BranchTable |