x64 new backend: port ABI implementation to shared infrastructure with AArch64.

Previously, in #2128, we factored out a common "vanilla 64-bit ABI"
implementation from the AArch64 ABI code, with the idea that this should
be largely compatible with x64. This PR alters the new x64 backend to
make use of the shared infrastructure, removing the duplication that
existed previously. The generated code is nearly (not exactly) the same;
the only difference relates to how the clobber-save region is padded in
the prologue.

This also changes some register allocations in the aarch64 code because
call support in the shared ABI infra now passes a temp vreg in, rather
than requiring use of a fixed, non-allocable temp; tests have been
updated, and the runtime behavior is unchanged.

cranelift/codegen/src/machinst/lower.rs

@@ -13,7 +13,7 @@ use crate::ir::{
     ValueDef,
 };
 use crate::machinst::{
-    ABIBody, BlockIndex, BlockLoweringOrder, LoweredBlock, MachLabel, VCode, VCodeBuilder,
+    ABICallee, BlockIndex, BlockLoweringOrder, LoweredBlock, MachLabel, VCode, VCodeBuilder,
     VCodeInst,
 };
 use crate::CodegenResult;
@@ -61,8 +61,8 @@ pub trait LowerCtx {
 
     // Function-level queries:
 
-    /// Get the `ABIBody`.
-    fn abi(&mut self) -> &dyn ABIBody<I = Self::I>;
+    /// Get the `ABICallee`.
+    fn abi(&mut self) -> &dyn ABICallee<I = Self::I>;
     /// Get the (virtual) register that receives the return value. A return
     /// instruction should lower into a sequence that fills this register. (Why
     /// not allow the backend to specify its own result register for the return?
@@ -312,7 +312,7 @@ impl<'func, I: VCodeInst> Lower<'func, I> {
     /// Prepare a new lowering context for the given IR function.
     pub fn new(
         f: &'func Function,
-        abi: Box<dyn ABIBody<I = I>>,
+        abi: Box<dyn ABICallee<I = I>>,
         block_order: BlockLoweringOrder,
     ) -> CodegenResult<Lower<'func, I>> {
         let mut vcode = VCodeBuilder::new(abi, block_order);
@@ -844,7 +844,7 @@ impl<'func, I: VCodeInst> Lower<'func, I> {
 impl<'func, I: VCodeInst> LowerCtx for Lower<'func, I> {
     type I = I;
 
-    fn abi(&mut self) -> &dyn ABIBody<I = I> {
+    fn abi(&mut self) -> &dyn ABICallee<I = I> {
         self.vcode.abi()
     }