Fix va_list handling for Windows Arm64 ABI

Author: Blackhex

gcc/config/aarch64/aarch64.cc

@@ -21484,6 +21484,17 @@ aarch64_expand_builtin_va_start (tree valist, rtx nextarg ATTRIBUTE_UNUSED)
   expand_expr (t, const0_rtx, VOIDmode, EXPAND_NORMAL);
 }
 
+#ifdef TARGET_AARCH64_MS_ABI
+
+static void
+aarch64_ms_abi_expand_builtin_va_start (tree valist, rtx nextarg)
+{
+  nextarg = plus_constant (Pmode, nextarg, cfun->machine->frame.first_vararg_offset, true);
+  std_expand_builtin_va_start (valist, nextarg);
+}
+
+#endif
+
 /* Implement TARGET_GIMPLIFY_VA_ARG_EXPR.  */
 
 static tree
@@ -21862,6 +21873,10 @@ aarch64_setup_incoming_varargs (cumulative_args_t cum_v,
     = (ROUND_UP (gr_saved * UNITS_PER_WORD,
 		 STACK_BOUNDARY / BITS_PER_UNIT)
        + vr_saved * UNITS_PER_VREG);
+
+#ifdef TARGET_AARCH64_MS_ABI
+  cfun->machine->frame.first_vararg_offset = -gr_saved * UNITS_PER_WORD;
+#endif
 }
 
 static void
@@ -22635,9 +22650,12 @@ static const char *
 aarch64_mangle_type (const_tree type)
 {
   /* The AArch64 ABI documents say that "__va_list" has to be
-     mangled as if it is in the "std" namespace.  */
+     mangled as if it is in the "std" namespace.
+     The Windows Arm64 ABI uses just an address of the first variadict argument.  */
+#ifndef TARGET_AARCH64_MS_ABI
   if (lang_hooks.types_compatible_p (CONST_CAST_TREE (type), va_list_type))
     return "St9__va_list";
+#endif
 
   /* Half-precision floating point types.  */
   if (SCALAR_FLOAT_TYPE_P (type) && TYPE_PRECISION (type) == 16)
@@ -30987,8 +31005,10 @@ aarch64_run_selftests (void)
 #undef TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY
 #define TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY aarch64_print_patchable_function_entry
 
+#ifndef TARGET_AARCH64_MS_ABI
 #undef TARGET_BUILD_BUILTIN_VA_LIST
 #define TARGET_BUILD_BUILTIN_VA_LIST aarch64_build_builtin_va_list
+#endif
 
 #undef TARGET_CALLEE_COPIES
 #define TARGET_CALLEE_COPIES hook_bool_CUMULATIVE_ARGS_arg_info_false
@@ -31059,7 +31079,11 @@ aarch64_run_selftests (void)
 #define TARGET_EXPAND_BUILTIN aarch64_expand_builtin
 
 #undef TARGET_EXPAND_BUILTIN_VA_START
+#ifdef TARGET_AARCH64_MS_ABI
+#define TARGET_EXPAND_BUILTIN_VA_START aarch64_ms_abi_expand_builtin_va_start
+#else
 #define TARGET_EXPAND_BUILTIN_VA_START aarch64_expand_builtin_va_start
+#endif
 
 #undef TARGET_FOLD_BUILTIN
 #define TARGET_FOLD_BUILTIN aarch64_fold_builtin
@@ -31099,8 +31123,10 @@ aarch64_run_selftests (void)
 #undef TARGET_GIMPLE_FOLD_BUILTIN
 #define TARGET_GIMPLE_FOLD_BUILTIN aarch64_gimple_fold_builtin
 
+#ifndef TARGET_AARCH64_MS_ABI
 #undef TARGET_GIMPLIFY_VA_ARG_EXPR
 #define TARGET_GIMPLIFY_VA_ARG_EXPR aarch64_gimplify_va_arg_expr
+#endif
 
 #undef  TARGET_INIT_BUILTINS
 #define TARGET_INIT_BUILTINS  aarch64_init_builtins

gcc/config/aarch64/aarch64.h

@@ -946,6 +946,11 @@ struct GTY (()) aarch64_frame
      STACK_BOUNDARY.  */
   HOST_WIDE_INT saved_varargs_size;
 
+#ifdef TARGET_AARCH64_MS_ABI
+  /* Offset to the first variadict argument on the stack.  */
+  HOST_WIDE_INT first_vararg_offset;
+#endif
+
   /* The number of bytes between the bottom of the static frame (the bottom
      of the outgoing arguments) and the bottom of the register save area.
      This value is always a multiple of STACK_BOUNDARY.  */