[v1,3/4] LoongArch: Disable relaxation if the assembler don't support conditional branch relaxation [PR112330]

Message ID 20240221031050.24343-4-chenglulu@loongson.cn
State New
Headers
Series Fix a series of problems caused by ASM_OUTPUT_ALIGN_WITH_NOP (release/gcc-12). |

Checks

Context Check Description
linaro-tcwg-bot/tcwg_gcc_build--master-aarch64 fail Patch failed to apply
linaro-tcwg-bot/tcwg_gcc_build--master-arm fail Patch failed to apply

Commit Message

Lulu Cheng Feb. 21, 2024, 3:10 a.m. UTC
  From: Xi Ruoyao <xry111@xry111.site>

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-driver.h (ASM_MRELAX_DEFAULT):
	Define.
	(ASM_MRELAX_SPEC): Define.
	(ASM_SPEC): Use ASM_MRELAX_SPEC instead of "%{mno-relax}".
	* config/loongarch/loongarch.cc: Take the setting of
	-m[no-]relax into account when determining the default of
	-mexplicit-relocs=.
	* doc/invoke.texi: Document -m[no-]relax and
	-m[no-]pass-mrelax-to-as for LoongArch.  Update the default
	value of -mexplicit-relocs=.

(cherry picked from commit fe23a2ff1f5072559552be0e41ab55bf72f5c79f)
---
 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(-)
  

Patch

diff --git a/gcc/config.in b/gcc/config.in
index f5b6287a96a..f3bdcb4cdda 100644
--- a/gcc/config.in
+++ b/gcc/config.in
@@ -367,6 +367,12 @@ 
 #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 edc2ed045d7..420a3941b3b 100644
--- a/gcc/config/loongarch/genopts/loongarch.opt.in
+++ b/gcc/config/loongarch/genopts/loongarch.opt.in
@@ -179,6 +179,10 @@  Target RejectNegative Joined Enum(cmodel) Var(la_opt_cmodel) Init(CMODEL_NORMAL)
 Specify the code model.
 
 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 60e682f57a0..bdf79ecc193 100644
--- a/gcc/config/loongarch/loongarch-opts.h
+++ b/gcc/config/loongarch/loongarch-opts.h
@@ -91,4 +91,8 @@  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 8d08b84c8eb..28ab87eb660 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 78b5e0cc452..3a39dcbd92e 100644
--- a/gcc/config/loongarch/loongarch.opt
+++ b/gcc/config/loongarch/loongarch.opt
@@ -186,6 +186,10 @@  Target RejectNegative Joined Enum(cmodel) Var(la_opt_cmodel) Init(CMODEL_NORMAL)
 Specify the code model.
 
 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 67cdd92a4f3..ac904c88f9f 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -28900,6 +28900,41 @@  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 e08ac5f4b49..87ae2d88e79 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -5340,6 +5340,16 @@  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 f4fdd8e6509..8f5c7abea64 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -1004,7 +1004,7 @@  Objective-C and Objective-C++ Dialects}.
 -mcond-move-float  -mno-cond-move-float @gol
 -memcpy  -mno-memcpy -mstrict-align -mno-strict-align @gol
 -mmax-inline-memcpy-size=@var{n} @gol
--mcmodel=@var{code-model}}
+-mcmodel=@var{code-model} -mrelax -mpass-mrelax-to-as}
 
 @emph{M32R/D Options}
 @gccoptlist{-m32r2  -m32rx  -m32r @gol
@@ -24626,6 +24626,28 @@  global symbol: The data got table must be within +/-8EiB addressing space.
 @end itemize
 @end table
 The default code model is @code{normal}.
+
+@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