[gcc r13-8351] LoongArch: Disable relaxation if the assembler don't support conditional branch relaxation [PR112330

[gcc r13-8351] LoongArch: Disable relaxation if the assembler don't support conditional branch relaxation [PR112330

[LuluCheng]

https://gcc.gnu.org/g:727ae33dae301d9ae5cc753493764ded1876a1ac

commit r13-8351-g727ae33dae301d9ae5cc753493764ded1876a1ac
Author: Xi Ruoyao <xry111@xry111.site>
Date:   Fri Nov 3 21:19:59 2023 +0800

    LoongArch: Disable relaxation if the assembler don't support conditional branch relaxation [PR112330]
    
    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:
---
 gcc/config.in                                 |  6 +++++
 gcc/config/loongarch/genopts/loongarch.opt.in |  6 ++++-
 gcc/config/loongarch/loongarch-opts.h         |  4 +++
 gcc/config/loongarch/loongarch.h              | 17 ++++++++++++-
 gcc/config/loongarch/loongarch.opt            |  6 ++++-
 gcc/configure                                 | 35 +++++++++++++++++++++++++++
 gcc/configure.ac                              | 10 ++++++++
 gcc/doc/invoke.texi                           | 24 +++++++++++++++++-
 8 files changed, 104 insertions(+), 4 deletions(-)

diff --git a/gcc/config.in b/gcc/config.in
index 36a74dd59748..83c98ae14574 100644
--- 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 e7c32e61a509..da6fedd153ef 100644
--- 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 7ea02f4978cc..edd41c82b177 100644
--- 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 cc719d0c7967..d072522e3cfe 100644
--- 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 e37ed9015de5..59b1e06d3f20 100644
--- 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 760bea9d4a0a..8a92601ef401 100755
--- 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 4f3c4ebb5a5f..f2e61a32d7ed 100644
--- 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 49941bf03701..99657fb44d86 100644
--- 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