Add a FixedTied constraint kind for operand constraints.

Fixes #175.

The Intel division instructions have fixed input operands that are
clobbered by fixed output operands, so the value passed as an input will
be clobbered just like a tied operand.

The FixedTied operand constraint is used to indicate a fixed input
operand that has a corresponding output operand with the same fixed
register.

Teach the spiller to teach a FixedTied operand the same as a Tied
operand constraint and make sure that the input value is killed by the
instruction.

cranelift/filetests/regalloc/output-interference.cton

@@ -0,0 +1,15 @@
+test compile
+set is_64bit=1
+isa intel haswell
+
+function %test(i64) -> i64 native {
+ebb0(v0: i64):
+    v2 = iconst.i64 12
+    ; This division clobbers two of its fixed input registers on Intel.
+    ; These are FixedTied constraints that the spiller needs to resolve.
+    v5 = udiv v0, v2
+    v6 = iconst.i64 13
+    v9 = udiv v0, v6
+    v10 = iadd v5, v9
+    return v10
+}

lib/cretonne/meta/cdsl/isa.py

@@ -394,6 +394,16 @@ class EncRecipe(object):
                 o2i[o] = i
         return (i2o, o2i)
 
+    def fixed_ops(self):
+        # type: () -> Tuple[Set[Register], Set[Register]]
+        """
+        Return two sets of registers representing the fixed input and output
+        operands.
+        """
+        i = set(r for r in self.ins if isinstance(r, Register))
+        o = set(r for r in self.outs if isinstance(r, Register))
+        return (i, o)
+
     def recipe_pred(self):
         # type: () -> RecipePred
         """

lib/cretonne/meta/cdsl/registers.py

@@ -286,7 +286,10 @@ class RegClass(object):
 
         For example: `GPR.r5`.
         """
-        return Register(self, self.bank.unit_by_name(attr))
+        reg = Register(self, self.bank.unit_by_name(attr))
+        # Save this register so we won't have to create it again.
+        setattr(self, attr, reg)
+        return reg
 
     def mask(self):
         # type: () -> List[int]

lib/cretonne/meta/gen_encoding.py

@@ -754,17 +754,14 @@ def emit_recipe_constraints(isa, fmt):
         for r in isa.all_recipes:
             fmt.comment(r.name)
             tied_i2o, tied_o2i = r.ties()
+            fixed_ins, fixed_outs = r.fixed_ops()
             with fmt.indented('RecipeConstraints {', '},'):
-                emit_operand_constraints(r, r.ins, 'ins', tied_i2o, fmt)
-                emit_operand_constraints(r, r.outs, 'outs', tied_o2i, fmt)
-                fmt.format(
-                        'fixed_ins: {},',
-                        str(any(isinstance(c, Register)
-                            for c in r.ins)).lower())
-                fmt.format(
-                        'fixed_outs: {},',
-                        str(any(isinstance(c, Register)
-                            for c in r.outs)).lower())
+                emit_operand_constraints(
+                    r, r.ins, 'ins', tied_i2o, fixed_outs, fmt)
+                emit_operand_constraints(
+                    r, r.outs, 'outs', tied_o2i, fixed_ins, fmt)
+                fmt.format('fixed_ins: {},', str(bool(fixed_ins)).lower())
+                fmt.format('fixed_outs: {},', str(bool(fixed_outs)).lower())
                 fmt.format('tied_ops: {},', str(bool(tied_i2o)).lower())
                 fmt.format(
                         'clobbers_flags: {},',
@@ -776,11 +773,16 @@ def emit_operand_constraints(
         seq,     # type: Sequence[OperandConstraint]
         field,   # type: str
         tied,    # type: Dict[int, int]
+        fixops,  # type: Set[Register]
         fmt      # type: srcgen.Formatter
         ):
     # type: (...) -> None
     """
     Emit a struct field initializer for an array of operand constraints.
+
+    :param field: The name of the struct field to emit.
+    :param tied: Map of tied opnums to counterparts.
+    :param fix_ops: Set of fixed operands on the other side of the inst.
     """
     if len(seq) == 0:
         fmt.line('{}: &[],'.format(field))
@@ -796,8 +798,9 @@ def emit_operand_constraints(
                     fmt.format('regclass: &{}_DATA,', cons)
                 elif isinstance(cons, Register):
                     assert n not in tied, "Can't tie fixed register operand"
-                    fmt.format(
-                            'kind: ConstraintKind::FixedReg({}),', cons.unit)
+                    # See if this fixed register is also on the other side.
+                    t = 'FixedTied' if cons in fixops else 'FixedReg'
+                    fmt.format('kind: ConstraintKind::{}({}),', t, cons.unit)
                     fmt.format('regclass: &{}_DATA,', cons.regclass)
                 elif isinstance(cons, int):
                     # This is a tied output constraint. It should never happen

lib/cretonne/src/isa/constraints.rs

@@ -37,7 +37,8 @@ impl OperandConstraint {
                     false
                 }
             }
-            ConstraintKind::FixedReg(reg) => {
+            ConstraintKind::FixedReg(reg) |
+            ConstraintKind::FixedTied(reg) => {
                 loc == ValueLoc::Reg(reg) && self.regclass.contains(reg)
             }
             ConstraintKind::Stack => {
@@ -73,6 +74,13 @@ pub enum ConstraintKind {
     /// the out operand is `Tied(in)`.
     Tied(u8),
 
+    /// This operand must be a fixed register, and it has a tied counterpart.
+    ///
+    /// This works just like `FixedReg`, but additionally indicates that there are identical
+    /// input/output operands for this fixed register. For an input operand, this means that the
+    /// value will be clobbered by the instruction
+    FixedTied(RegUnit),
+
     /// This operand must be a value in a stack slot.
     ///
     /// The constraint's `regclass` field is the register class that would normally be used to load

lib/cretonne/src/regalloc/coloring.rs

@@ -478,7 +478,8 @@ impl<'a> Context<'a> {
             // already in a register.
             let cur_reg = self.divert.reg(value, &self.cur.func.locations);
             match op.kind {
-                ConstraintKind::FixedReg(regunit) => {
+                ConstraintKind::FixedReg(regunit) |
+                ConstraintKind::FixedTied(regunit) => {
                     if regunit != cur_reg {
                         self.solver.reassign_in(
                             value,
@@ -532,7 +533,9 @@ impl<'a> Context<'a> {
                         }
                     }
                 }
-                _ => {}
+                ConstraintKind::FixedReg(_) |
+                ConstraintKind::FixedTied(_) |
+                ConstraintKind::Stack => {}
             }
         }
     }
@@ -674,8 +677,15 @@ impl<'a> Context<'a> {
         throughs: &[LiveValue],
     ) {
         for (op, lv) in constraints.iter().zip(defs) {
-            if let ConstraintKind::FixedReg(reg) = op.kind {
-                self.add_fixed_output(lv.value, op.regclass, reg, throughs);
+            match op.kind {
+                ConstraintKind::FixedReg(reg) |
+                ConstraintKind::FixedTied(reg) => {
+                    self.add_fixed_output(lv.value, op.regclass, reg, throughs);
+                }
+                ConstraintKind::Reg |
+                ConstraintKind::Tied(_) |
+                ConstraintKind::Stack => {}
+
             }
         }
     }
@@ -741,6 +751,7 @@ impl<'a> Context<'a> {
         for (op, lv) in constraints.iter().zip(defs) {
             match op.kind {
                 ConstraintKind::FixedReg(_) |
+                ConstraintKind::FixedTied(_) |
                 ConstraintKind::Stack => continue,
                 ConstraintKind::Reg => {
                     self.solver.add_def(lv.value, op.regclass, !lv.is_local);

lib/cretonne/src/regalloc/spilling.rs

@@ -301,6 +301,10 @@ impl<'a> Context<'a> {
                     // A tied operand must kill the used value.
                     reguse.tied = !lr.killed_at(inst, ebb, &self.cur.func.layout);
                 }
+                ConstraintKind::FixedTied(_) => {
+                    reguse.fixed = true;
+                    reguse.tied = !lr.killed_at(inst, ebb, &self.cur.func.layout);
+                }
                 ConstraintKind::Reg => {}
             }
             if lr.affinity.is_stack() {