Add a TargetIsa::regclass_for_abi_type() function.

The legalize_signature() function will return ArgumentLoc::Reg arguments
that contain a register unit. However, the register also needs to be
able to associate a register class with the argument values to fully
track the used registers.

When values are defined by instructions, the register class is part for
the operand constraints for the instruction. For values defined on ABI
boundaries like function arguments and return values from a call, the
register class is provided by the new regclass_for_abi_type() function.

Provide implementations of this function in abi modules of all the
targets, even those that don't have a legalize_signature()
implementation yet.

Since we're adding abi modules to all targets, move the
legalize_signature() stubs in there and make the function mandatory in
TargetIsa. All targets will eventually need this function.

lib/cretonne/src/isa/intel/mod.rs

@@ -1,6 +1,7 @@
 //! Intel Instruction Set Architectures.
 
 pub mod settings;
+mod abi;
 mod binemit;
 mod enc_tables;
 mod registers;
@@ -9,7 +10,7 @@ use binemit::CodeSink;
 use super::super::settings as shared_settings;
 use isa::enc_tables::{self as shared_enc_tables, lookup_enclist, general_encoding};
 use isa::Builder as IsaBuilder;
-use isa::{TargetIsa, RegInfo, EncInfo, Encoding, Legalize};
+use isa::{TargetIsa, RegInfo, RegClass, EncInfo, Encoding, Legalize};
 use ir;
 
 #[allow(dead_code)]
@@ -77,6 +78,14 @@ impl TargetIsa for Isa {
                 })
     }
 
+    fn legalize_signature(&self, sig: &mut ir::Signature, current: bool) {
+        abi::legalize_signature(sig, &self.shared_flags, current)
+    }
+
+    fn regclass_for_abi_type(&self, ty: ir::Type) -> RegClass {
+        abi::regclass_for_abi_type(ty)
+    }
+
     fn emit_inst(&self, func: &ir::Function, inst: ir::Inst, sink: &mut CodeSink) {
         binemit::emit_inst(func, inst, sink)
     }