LoongArch: Disable relaxation if the assembler don't support conditional branch relax...

As the commit message of r14-4674 has indicated, if the assembler does
not support conditional branch relaxation, a relocation overflow may
happen on conditional branches when relaxation is enabled because the
number of NOP instructions inserted by the assembler will be more than
the number estimated by GCC.

To work around this issue, disable relaxation by default if the
assembler is detected incapable to perform conditional branch relaxation
at GCC build time.  We also need to pass -mno-relax to the assembler to
really disable relaxation.  But, if the assembler does not support
-mrelax option at all, we should not pass -mno-relax to the assembler or
it will immediately error out.  Also handle this with the build time
assembler capability probing, and add a pair of options
-m[no-]pass-mrelax-to-as to allow using a different assembler from the
build-time one.

With this change, if GCC is built with GAS 2.41, relaxation will be
disabled by default.  So the default value of -mexplicit-relocs= is also
changed to 'always' if -mno-relax is specified or implied by the
build-time default, because using assembler macros for symbol addresses
produces no benefit when relaxation is disabled.

gcc/ChangeLog:

	PR target/112330
	* config/loongarch/genopts/loongarch.opt.in: Add
	-m[no]-pass-relax-to-as.  Change the default of -m[no]-relax to
	account conditional branch relaxation support status.
	* config/loongarch/loongarch.opt: Regenerate.
	* configure.ac (gcc_cv_as_loongarch_cond_branch_relax): Check if
	the assembler supports conditional branch relaxation.
	* configure: Regenerate.
	* config.in: Regenerate.  Note that there are some unrelated
	changes introduced by r14-5424 (which does not contain a
	config.in regeneration).
	* config/loongarch/loongarch-opts.h
	(HAVE_AS_COND_BRANCH_RELAXATION): Define to 0 if not defined.
	* config/loongarch/loongarch.h (ASM_MRELAX_DEFAULT): Define.
	(ASM_MRELAX_SPEC): Define.
	(ASM_SPEC): Use ASM_MRELAX_SPEC instead of "%{mno-relax}".
	* doc/invoke.texi: Document -m[no-]relax and
	-m[no-]pass-mrelax-to-as for LoongArch.

(cherry picked from commit fe23a2ff1f5072559552be0e41ab55bf72f5c79f)

diff --git a/gcc/config.in b/gcc/config.in
index 36a74dd597489186123cbacecf51b8dd56860bef..83c98ae14574d446d3f9d32aeb21c642c70580b9 100644 (file)
--- a/gcc/config.in
+++ b/gcc/config.in
@@ -373,6 +373,12 @@
 #endif
 
 
+/* Define if your assembler supports conditional branch relaxation. */
+#ifndef USED_FOR_TARGET
+#undef HAVE_AS_COND_BRANCH_RELAXATION
+#endif
+
+
 /* Define if your assembler supports the --debug-prefix-map option. */
 #ifndef USED_FOR_TARGET
 #undef HAVE_AS_DEBUG_PREFIX_MAP

diff --git a/gcc/config/loongarch/genopts/loongarch.opt.in b/gcc/config/loongarch/genopts/loongarch.opt.in
index e7c32e61a509140803e34d8fae56c1179cb11c8e..da6fedd153efbe14dec15552bf43c242ec90ff76 100644 (file)
--- a/gcc/config/loongarch/genopts/loongarch.opt.in
+++ b/gcc/config/loongarch/genopts/loongarch.opt.in
@@ -190,6 +190,10 @@ Target Var(TARGET_DIRECT_EXTERN_ACCESS) Init(0)
 Avoid using the GOT to access external symbols.
 
 mrelax
-Target Var(loongarch_mrelax) Init(HAVE_AS_MRELAX_OPTION)
+Target Var(loongarch_mrelax) Init(HAVE_AS_MRELAX_OPTION && HAVE_AS_COND_BRANCH_RELAXATION)
 Take advantage of linker relaxations to reduce the number of instructions
 required to materialize symbol addresses.
+
+mpass-mrelax-to-as
+Target Var(loongarch_pass_mrelax_to_as) Init(HAVE_AS_MRELAX_OPTION)
+Pass -mrelax or -mno-relax option to the assembler.

diff --git a/gcc/config/loongarch/loongarch-opts.h b/gcc/config/loongarch/loongarch-opts.h
index 7ea02f4978ccd201c985154544462f1f7e92cfd8..edd41c82b1774e2e028c2f1f6a74b879f60987aa 100644 (file)
--- a/gcc/config/loongarch/loongarch-opts.h
+++ b/gcc/config/loongarch/loongarch-opts.h
@@ -96,4 +96,8 @@ loongarch_config_target (struct loongarch_target *target,
 #define HAVE_AS_MRELAX_OPTION 0
 #endif
 
+#ifndef HAVE_AS_COND_BRANCH_RELAXATION
+#define HAVE_AS_COND_BRANCH_RELAXATION 0
+#endif
+
 #endif /* LOONGARCH_OPTS_H */

diff --git a/gcc/config/loongarch/loongarch.h b/gcc/config/loongarch/loongarch.h
index cc719d0c796747888d7ec85e3cad4a959f2c776e..d072522e3cfe7832ef58d9a3b5b13472e8a64ac8 100644 (file)
--- a/gcc/config/loongarch/loongarch.h
+++ b/gcc/config/loongarch/loongarch.h
@@ -69,8 +69,23 @@ along with GCC; see the file COPYING3.  If not see
 #define SUBTARGET_ASM_SPEC ""
 #endif
 
+#if HAVE_AS_MRELAX_OPTION && HAVE_AS_COND_BRANCH_RELAXATION
+#define ASM_MRELAX_DEFAULT "%{!mrelax:%{!mno-relax:-mrelax}}"
+#else
+#define ASM_MRELAX_DEFAULT "%{!mrelax:%{!mno-relax:-mno-relax}}"
+#endif
+
+#if HAVE_AS_MRELAX_OPTION
+#define ASM_MRELAX_SPEC \
+  "%{!mno-pass-mrelax-to-as:%{mrelax} %{mno-relax} " ASM_MRELAX_DEFAULT "}"
+#else
+#define ASM_MRELAX_SPEC \
+  "%{mpass-mrelax-to-as:%{mrelax} %{mno-relax} " ASM_MRELAX_DEFAULT "}"
+#endif
+
 #undef ASM_SPEC
-#define ASM_SPEC "%{mabi=*} %{subtarget_asm_spec}"
+#define ASM_SPEC \
+  "%{mabi=*} " ASM_MRELAX_SPEC " %(subtarget_asm_spec)"
 
 /* Extra switches sometimes passed to the linker.  */
 

diff --git a/gcc/config/loongarch/loongarch.opt b/gcc/config/loongarch/loongarch.opt
index e37ed9015de55096a16cbb5d1800c83aa2afbec3..59b1e06d3f2040f93c25656af7c5b92952e82a59 100644 (file)
--- a/gcc/config/loongarch/loongarch.opt
+++ b/gcc/config/loongarch/loongarch.opt
@@ -197,6 +197,10 @@ Target Var(TARGET_DIRECT_EXTERN_ACCESS) Init(0)
 Avoid using the GOT to access external symbols.
 
 mrelax
-Target Var(loongarch_mrelax) Init(HAVE_AS_MRELAX_OPTION)
+Target Var(loongarch_mrelax) Init(HAVE_AS_MRELAX_OPTION && HAVE_AS_COND_BRANCH_RELAXATION)
 Take advantage of linker relaxations to reduce the number of instructions
 required to materialize symbol addresses.
+
+mpass-mrelax-to-as
+Target Var(loongarch_pass_mrelax_to_as) Init(HAVE_AS_MRELAX_OPTION)
+Pass -mrelax or -mno-relax option to the assembler.

diff --git a/gcc/configure b/gcc/configure
index 760bea9d4a0a147ae98440ed06ecb2f9ac007bff..8a92601ef401a742005d7bea5fb23e2bc94e0149 100755 (executable)
--- a/gcc/configure
+++ b/gcc/configure
@@ -29106,6 +29106,41 @@ if test $gcc_cv_as_loongarch_relax = yes; then
 
 $as_echo "#define HAVE_AS_MRELAX_OPTION 1" >>confdefs.h
 
+fi
+
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking assembler for conditional branch relaxation support" >&5
+$as_echo_n "checking assembler for conditional branch relaxation support... " >&6; }
+if ${gcc_cv_as_loongarch_cond_branch_relax+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  gcc_cv_as_loongarch_cond_branch_relax=no
+  if test x$gcc_cv_as != x; then
+    $as_echo 'a:
+       .rept 32769
+       nop
+       .endr
+       beq $a0,$a1,a' > conftest.s
+    if { ac_try='$gcc_cv_as $gcc_cv_as_flags --fatal-warnings -o conftest.o conftest.s >&5'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; }
+    then
+       gcc_cv_as_loongarch_cond_branch_relax=yes
+    else
+      echo "configure: failed program was" >&5
+      cat conftest.s >&5
+    fi
+    rm -f conftest.o conftest.s
+  fi
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $gcc_cv_as_loongarch_cond_branch_relax" >&5
+$as_echo "$gcc_cv_as_loongarch_cond_branch_relax" >&6; }
+if test $gcc_cv_as_loongarch_cond_branch_relax = yes; then
+
+$as_echo "#define HAVE_AS_COND_BRANCH_RELAXATION 1" >>confdefs.h
+
 fi
 
     ;;

diff --git a/gcc/configure.ac b/gcc/configure.ac
index 4f3c4ebb5a5f3d76ac35d6af2c7d7c111ca6dbd9..f2e61a32d7eddd704a0d3b83318f8bf536610dd3 100644 (file)
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -5370,6 +5370,16 @@ x:
       [-mrelax], [.text],,
       [AC_DEFINE(HAVE_AS_MRELAX_OPTION, 1,
                [Define if your assembler supports -mrelax option.])])
+    gcc_GAS_CHECK_FEATURE([conditional branch relaxation support],
+      gcc_cv_as_loongarch_cond_branch_relax,
+      [--fatal-warnings],
+      [a:
+       .rept 32769
+       nop
+       .endr
+       beq $a0,$a1,a],,
+      [AC_DEFINE(HAVE_AS_COND_BRANCH_RELAXATION, 1,
+               [Define if your assembler supports conditional branch relaxation.])])
     ;;
     s390*-*-*)
     gcc_GAS_CHECK_FEATURE([.gnu_attribute support],

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 49941bf0370158082a69373b8035b1d37996b4d3..99657fb44d86a4ba1532cd35169f1d50e44ae805 100644 (file)
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -1030,7 +1030,7 @@ Objective-C and Objective-C++ Dialects}.
 -mmax-inline-memcpy-size=@var{n}
 -mexplicit-relocs -mno-explicit-relocs
 -mdirect-extern-access -mno-direct-extern-access
--mcmodel=@var{code-model}}
+-mcmodel=@var{code-model} -mrelax -mpass-mrelax-to-as}
 
 @emph{M32R/D Options}
 @gccoptlist{-m32r2  -m32rx  -m32r
@@ -25850,6 +25850,28 @@ environments where no dynamic link is performed, like firmwares, OS
 kernels, executables linked with @option{-static} or @option{-static-pie}.
 @option{-mdirect-extern-access} is not compatible with @option{-fPIC} or
 @option{-fpic}.
+
+@item -mrelax
+@itemx -mno-relax
+Take (do not take) advantage of linker relaxations.  If
+@option{-mpass-mrelax-to-as} is enabled, this option is also passed to
+the assembler.  The default is determined during GCC build-time by
+detecting corresponding assembler support:
+@option{-mrelax} if the assembler supports both the @option{-mrelax}
+option and the conditional branch relaxation (it's required or the
+@code{.align} directives and conditional branch instructions in the
+assembly code outputted by GCC may be rejected by the assembler because
+of a relocation overflow), @option{-mno-relax} otherwise.
+
+@item -mpass-mrelax-to-as
+@itemx -mno-pass-mrelax-to-as
+Pass (do not pass) the @option{-mrelax} or @option{-mno-relax} option
+to the assembler.  The default is determined during GCC build-time by
+detecting corresponding assembler support:
+@option{-mpass-mrelax-to-as} if the assembler supports the
+@option{-mrelax} option, @option{-mno-pass-mrelax-to-as} otherwise.
+This option is mostly useful for debugging, or interoperation with
+assemblers different from the build-time one.
 @end table
 
 @node M32C Options