gdb: Enable finish command and inferior calls for _Float16 on amd64 and i386.

Values of type _Float16 and _Float16 _Complex can now be used on CPUs with
AVX512-FP16 support. Return values of those types are located in XMM0.
Compiler support for gcc and clang is in progress, see e.g.:
https://gcc.gnu.org/pipermail/gcc-patches/2021-July/574117.html

gdb/ChangeLog:
2021-07-21  Felix Willgerodt  <Felix.Willgerodt@intel.com>

	* amd64-tdep.c (amd64_classify): Classify _Float16 and
	_Float16 _Complex as AMD64_SSE.
	* i386-tdep.c (i386_extract_return_value): Read _Float16 and
	_Float16 _Complex from xmm0.

gdb/testsuite/ChangeLog:
2021-07-21  Felix Willgerodt  <Felix.Willgerodt@intel.com>

	* gdb.arch/x86-avx512fp16-abi.c: New file.
	* gdb.arch/x86-avx512fp16-abi.exp: New file.

gdb/amd64-tdep.c

@@ -728,10 +728,10 @@ amd64_classify (struct type *type, enum amd64_reg_class theclass[2])
       && (len == 1 || len == 2 || len == 4 || len == 8))
     theclass[0] = AMD64_INTEGER;
 
-  /* Arguments of types float, double, _Decimal32, _Decimal64 and __m64
-     are in class SSE.  */
+  /* Arguments of types _Float16, float, double, _Decimal32, _Decimal64 and
+     __m64 are in class SSE.  */
   else if ((code == TYPE_CODE_FLT || code == TYPE_CODE_DECFLOAT)
-	   && (len == 4 || len == 8))
+	   && (len == 2 || len == 4 || len == 8))
     /* FIXME: __m64 .  */
     theclass[0] = AMD64_SSE;
 
@@ -749,8 +749,8 @@ amd64_classify (struct type *type, enum amd64_reg_class theclass[2])
     /* Class X87 and X87UP.  */
     theclass[0] = AMD64_X87, theclass[1] = AMD64_X87UP;
 
-  /* Arguments of complex T where T is one of the types float or
-     double get treated as if they are implemented as:
+  /* Arguments of complex T - where T is one of the types _Float16, float or
+     double - get treated as if they are implemented as:
 
      struct complexT {
        T real;
@@ -758,7 +758,7 @@ amd64_classify (struct type *type, enum amd64_reg_class theclass[2])
      };
 
   */
-  else if (code == TYPE_CODE_COMPLEX && len == 8)
+  else if (code == TYPE_CODE_COMPLEX && (len == 8 || len == 4))
     theclass[0] = AMD64_SSE;
   else if (code == TYPE_CODE_COMPLEX && len == 16)
     theclass[0] = theclass[1] = AMD64_SSE;

gdb/i386-tdep.c

@@ -2818,7 +2818,14 @@ i386_extract_return_value (struct gdbarch *gdbarch, struct type *type,
   int len = TYPE_LENGTH (type);
   gdb_byte buf[I386_MAX_REGISTER_SIZE];
 
-  if (type->code () == TYPE_CODE_FLT)
+  /* _Float16 and _Float16 _Complex values are returned via xmm0.  */
+  if (((type->code () == TYPE_CODE_FLT) && len == 2)
+      || ((type->code () == TYPE_CODE_COMPLEX) && len == 4))
+    {
+	regcache->raw_read (I387_XMM0_REGNUM (tdep), valbuf);
+	return;
+    }
+  else if (type->code () == TYPE_CODE_FLT)
     {
       if (tdep->st0_regnum < 0)
 	{

gdb/testsuite/gdb.arch/x86-avx512fp16-abi.c

@@ -0,0 +1,38 @@
+/* Test program for _Float16 parameters and return values.
+
+   Copyright 2021 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+#include <complex.h>
+
+_Float16
+square (_Float16 num) {
+  return num * num; /* BP1.  */
+}
+
+_Float16 _Complex
+plus (_Float16 _Complex num) {
+  return num + (2.5 + 0.5I); /* BP2.  */
+}
+
+int
+main ()
+{
+  _Float16 a = square (1.25);
+  _Float16 _Complex b = 6.25 + I;
+  _Float16 _Complex ret = plus (b); /* BP3.  */
+  return 0;
+}

gdb/testsuite/gdb.arch/x86-avx512fp16-abi.exp

@@ -0,0 +1,63 @@
+# Copyright 2021 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test support for _Float16 parameters and return values.
+
+if { [skip_avx512fp16_tests] } {
+    unsupported "target does not support AVX512fp16"
+    return -1
+}
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile} \
+     {debug additional_flags="-mavx512fp16"}] } {
+    return -1
+}
+
+if { ![runto_main] } {
+    unsupported "could not run to main"
+    return -1
+}
+
+gdb_test "p square(2.2)" "= 4\\.8359"
+
+set line1 [gdb_get_line_number "BP1"]
+set line2 [gdb_get_line_number "BP2"]
+set line3 [gdb_get_line_number "BP3"]
+gdb_breakpoint $line1
+gdb_breakpoint $line3
+
+gdb_continue_to_breakpoint "line1" ".*$srcfile:$line1.*"
+
+with_test_prefix "real" {
+    gdb_test "p num" "= 1\\.25"
+    gdb_test "ptype num" "type = _Float16"
+    gdb_test "finish" "Value returned is.*= 1\\.5625"
+}
+
+gdb_continue_to_breakpoint "line3" ".*$srcfile:$line3.*"
+gdb_test "p plus(b)" "= 8\\.75 \\+ 1\\.5i"
+
+gdb_breakpoint $line2
+gdb_continue_to_breakpoint "line2" ".*$srcfile:$line2.*"
+
+with_test_prefix "complex" {
+    gdb_test "p num" "= 6\\.25 \\+ 1i"
+    gdb_test "ptype num" "type = complex _Float16"
+    gdb_test "finish" "Value returned is.*= 8\\.75 \\+ 1\\.5i"
+}
+
+gdb_continue_to_end