From 18e2e589eefc9ac96a75ff890cf883f754b163e4 Mon Sep 17 00:00:00 2001
From: Yang Yujie <yangyujie@loongson.cn>
Date: Mon, 28 Aug 2023 10:20:12 +0800
Subject: [PATCH] LoongArch: add new configure option --with-strict-align-lib

LoongArch processors may not support memory accesses without natural
alignments.  Building libraries with -mstrict-align may help with
toolchain binary compatiblity and performance on these implementations
(e.g. Loongson 2K1000LA).

No significant performance degredation is observed on current mainstream
LoongArch processors when the option is enabled.

gcc/ChangeLog:

	* config.gcc: use -mstrict-align for building libraries
	if --with-strict-align-lib is given.
	* doc/install.texi: likewise.
---
 gcc/config.gcc       | 16 +++++++++++++++-
 gcc/doc/install.texi |  4 ++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/gcc/config.gcc b/gcc/config.gcc
index 543b0ba076ba..89af167e5d94 100644
--- a/gcc/config.gcc
+++ b/gcc/config.gcc
@@ -4892,7 +4892,7 @@ case "${target}" in
 		;;
 
 	loongarch*-*)
-		supported_defaults="abi arch tune fpu simd multilib-default"
+		supported_defaults="abi arch tune fpu simd multilib-default strict-align-lib"
 
 		# Local variables
 		unset \
@@ -5089,6 +5089,17 @@ case "${target}" in
 			;;
 		esac
 
+		# Build libraries with -mstrict-align if --with-strict-align-lib is given.
+		case ${with_strict_align_lib} in
+		yes) strict_align_opt="/mstrict-align" ;;
+		""|no)  ;;
+		*)
+			echo "Unknown option: --with-strict-align-lib=${with_strict_align_lib}" 1>&2
+			exit 1
+			;;
+		esac
+
+
 		# Handle --with-multilib-default
 		if echo "${with_multilib_default}" \
 		| grep -E -e '[[:space:]]' -e '//' -e '/$' -e '^/' > /dev/null 2>&1; then
@@ -5250,6 +5261,9 @@ case "${target}" in
 					;;
 			esac
 
+			# Use mstrict-align for building libraries if --with-strict-align-lib is given.
+			loongarch_multilib_list_make="${loongarch_multilib_list_make}${strict_align_opt}"
+
 			# Check for repeated configuration of the same multilib variant.
 			if echo "${elem_abi_base}/${elem_abi_ext}" \
 			 | grep -E "^(${all_abis%|})$" >/dev/null 2>&1; then
diff --git a/gcc/doc/install.texi b/gcc/doc/install.texi
index bbc58cb60caf..31f2234640f8 100644
--- a/gcc/doc/install.texi
+++ b/gcc/doc/install.texi
@@ -1416,6 +1416,10 @@ Multiple @var{option}s may appear consecutively while @var{arch} may only
 appear in the beginning or be omitted (which means @option{-march=abi-default}
 is applied when building the libraries).
 
+@item --with-strict-align-lib
+On LoongArch targets, build all enabled multilibs with @option{-mstrict-align}
+(Not enabled by default).
+
 @item --with-multilib-generator=@var{config}
 Specify what multilibs to build.  @var{config} is a semicolon separated list of
 values, possibly consisting of a single value.  Currently only implemented
-- 
2.47.2