Darwin, Arm64 : Adjust cases where stack spills pack differently.

+ Temporary handling for complex values.

Complex values with a total size less than one stack slot might
conceivably be packed in the same manner as other small values.

However, this is not done - and we need to override the process
for them.

+ Don't pack small structs either.

Darwinpcs doesn't mention some things - and one is small structs.

These are put into regs - but, when they spill to the stack, they don't
pack in the manner of char, int et. al.

+ Handle HFA cases that have packed stack layout.

bleah! (not sure this is complete).

+ Exclude unions from packing rule.

+ Hide an unused function.

We are not using aarch64_vfp_is_call_candidate so wrap it
in an #ifdef.

+ Fix a build error.

Drop an unused var.

gcc/config/aarch64/aarch64.cc

@@ -6626,6 +6626,7 @@ aarch64_return_in_memory (const_tree type, const_tree fndecl ATTRIBUTE_UNUSED)
   gcc_unreachable ();
 }
 
+#if !TARGET_MACHO
 static bool
 aarch64_vfp_is_call_candidate (cumulative_args_t pcum_v, machine_mode mode,
 			       const_tree type, int *nregs)
@@ -6635,6 +6636,7 @@ aarch64_vfp_is_call_candidate (cumulative_args_t pcum_v, machine_mode mode,
 						  &pcum->aapcs_vfp_rmode,
 						  nregs, NULL, pcum->silent_p);
 }
+#endif
 
 /* Given MODE and TYPE of a function argument, return the alignment in
    bits.  The idea is to suppress any stronger alignment requested by
@@ -6778,10 +6780,18 @@ aarch64_layout_arg (cumulative_args_t pcum_v, const function_arg_info &arg)
   size = ROUND_UP (size, UNITS_PER_WORD);
 
   allocate_ncrn = (type) ? !(FLOAT_TYPE_P (type)) : !FLOAT_MODE_P (mode);
+  bool is_ha = false;
+#if !TARGET_MACHO
   allocate_nvrn = aarch64_vfp_is_call_candidate (pcum_v,
 						 mode,
 						 type,
 						 &nregs);
+#else
+  allocate_nvrn = aarch64_vfp_is_call_or_return_candidate (mode, type,
+						  &pcum->aapcs_vfp_rmode,
+						  &nregs, &is_ha,
+						  pcum->silent_p);
+#endif
   gcc_assert (!sve_p || !allocate_nvrn);
 
   /* allocate_ncrn may be false-positive, but allocate_nvrn is quite reliable.
@@ -6943,9 +6953,15 @@ aarch64_layout_arg (cumulative_args_t pcum_v, const function_arg_info &arg)
 	 at the end.  When the current position is 0 - any allocation needs
 	 a stack slot.  CHECKME: do we need to align 16byte entities?
 
-	 but we don't do this for unnamed parms in variadic functions, they
+	 but we don't do this for:
+	  * unnamed parms in variadic functions
+	  * complex types smaller than 4 bytes
 	 each get their own slot.  */
-      if (!arg.named)
+      if (!arg.named
+	  || TREE_CODE (type) == COMPLEX_TYPE
+	  || (TREE_CODE (type) == RECORD_TYPE
+	      && !is_ha && !SCALAR_FLOAT_MODE_P (pcum->aapcs_vfp_rmode))
+	  || TREE_CODE (type) == UNION_TYPE)
 	{
 	  pcum->aapcs_stack_words = size / UNITS_PER_WORD;
 	  pcum->darwinpcs_sub_word_offset = 0;
@@ -7032,6 +7048,7 @@ aarch64_init_cumulative_args (CUMULATIVE_ARGS *pcum,
   pcum->darwinpcs_sub_word_offset = 0;
   pcum->darwinpcs_sub_word_pos = 0;
   pcum->silent_p = silent_p;
+  pcum->aapcs_vfp_rmode = VOIDmode;
 
   if (!silent_p
       && !TARGET_FLOAT
@@ -7105,12 +7122,23 @@ aarch64_function_arg_regno_p (unsigned regno)
 static unsigned int
 aarch64_function_arg_boundary (machine_mode mode, const_tree type)
 {
-#if TARGET_MACHO
-  return MIN (alignment, STACK_BOUNDARY);
-#else
   unsigned int abi_break;
   unsigned int alignment = aarch64_function_arg_alignment (mode, type,
 							   &abi_break);
+#if TARGET_MACHO
+  /* Temporary fudge to put some non-scalar types in distinct stack slots.  */
+  machine_mode comp_mode = VOIDmode;
+  int nregs;
+  bool is_ha;
+  aarch64_vfp_is_call_or_return_candidate (mode, type, &comp_mode, &nregs,
+					   &is_ha, /*silent*/true);
+  if (TREE_CODE (type) == COMPLEX_TYPE
+      || (TREE_CODE (type) == RECORD_TYPE
+	  && !is_ha && !SCALAR_FLOAT_MODE_P (comp_mode))
+      || TREE_CODE (type) == UNION_TYPE)
+    return MIN (MAX (alignment, PARM_BOUNDARY), STACK_BOUNDARY);
+  return MIN (alignment, STACK_BOUNDARY);
+#else
   alignment = MIN (MAX (alignment, PARM_BOUNDARY), STACK_BOUNDARY);
   if (abi_break & warn_psabi)
     {