gcc: xtensa: add -m[no-]strict-align option

gcc/
	* config/xtensa/xtensa-opts.h: New header.
	* config/xtensa/xtensa.h (STRICT_ALIGNMENT): Redefine as
	xtensa_strict_align.
	* config/xtensa/xtensa.cc (xtensa_option_override): When
	-m[no-]strict-align is not specified in the command line set
	xtensa_strict_align to 0 if the hardware supports both unaligned
	loads and stores or to 1 otherwise.
	* config/xtensa/xtensa.opt (mstrict-align): New option.
	* doc/invoke.texi (Xtensa Options): Document -m[no-]strict-align.

gcc/config/xtensa/xtensa-opts.h

@@ -0,0 +1,28 @@
+/* Definitions for option handling for Xtensa.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC 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, or (at your option)
+any later version.
+
+GCC 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 GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#ifndef XTENSA_OPTS_H
+#define XTENSA_OPTS_H
+
+/* Undefined state for the -mstrict-alignment option  */
+enum xtensa_strict_alignment_setting {
+  XTENSA_STRICT_ALIGNMENT_UNDEFINED = -1,
+};
+
+#endif

gcc/config/xtensa/xtensa.cc

@@ -2792,6 +2792,10 @@ xtensa_option_override (void)
   if (xtensa_windowed_abi == -1)
     xtensa_windowed_abi = TARGET_WINDOWED_ABI_DEFAULT;
 
+  if (xtensa_strict_alignment == XTENSA_STRICT_ALIGNMENT_UNDEFINED)
+    xtensa_strict_alignment = !XCHAL_UNALIGNED_LOAD_HW
+      || !XCHAL_UNALIGNED_STORE_HW;
+
   if (! TARGET_THREADPTR)
     targetm.have_tls = false;
 

gcc/config/xtensa/xtensa.h

@@ -143,7 +143,7 @@ along with GCC; see the file COPYING3.  If not see
 
 /* Set this nonzero if move instructions will actually fail to work
    when given unaligned data.  */
-#define STRICT_ALIGNMENT 1
+#define STRICT_ALIGNMENT (xtensa_strict_alignment)
 
 /* Promote integer modes smaller than a word to SImode.  Set UNSIGNEDP
    for QImode, because there is no 8-bit load from memory with sign

gcc/config/xtensa/xtensa.opt

@@ -18,6 +18,9 @@
 ; along with GCC; see the file COPYING3.  If not see
 ; <http://www.gnu.org/licenses/>.
 
+HeaderInclude
+config/xtensa/xtensa-opts.h
+
 mconst16
 Target Mask(CONST16)
 Use CONST16 instruction to load constants.
@@ -64,3 +67,7 @@ Use call0 ABI.
 mabi=windowed
 Target RejectNegative Var(xtensa_windowed_abi, 1)
 Use windowed registers ABI.
+
+mstrict-align
+Target Var(xtensa_strict_alignment) Init(XTENSA_STRICT_ALIGNMENT_UNDEFINED)
+Do not use unaligned memory references.

gcc/doc/invoke.texi

@@ -1474,7 +1474,8 @@ See RS/6000 and PowerPC Options.
 -mtarget-align  -mno-target-align
 -mlongcalls  -mno-longcalls
 -mabi=@var{abi-type}
--mextra-l32r-costs=@var{cycles}}
+-mextra-l32r-costs=@var{cycles}
+-mstrict-align  -mno-strict-align}
 
 @emph{zSeries Options}
 See S/390 and zSeries Options.
@@ -34401,6 +34402,17 @@ instructions, in clock cycles.  This affects, when optimizing for speed,
 whether loading a constant from literal pool using @code{L32R} or
 synthesizing the constant from a small one with a couple of arithmetic
 instructions.  The default value is 0.
+
+@opindex mstrict-align
+@opindex mno-strict-align
+@item -mstrict-align
+@itemx -mno-strict-align
+Avoid or allow generating memory accesses that may not be aligned on a natural
+object boundary as described in the architecture specification.
+The default is @option{-mno-strict-align} for cores that support both
+unaligned loads and stores in hardware and @option{-mstrict-align} for all
+other cores.
+
 @end table
 
 @node zSeries Options