arm: pass architecture extensions to assembler if supported

When I originally added the new extended architecture features support
to GCC, the assembler was unable to parse the new feature lists on the
command-line and would throw an error.  This has now been fixed in GAS
and the behaviour is the same as GCC.

So this patch adds a configure-time test for the assembler in use to
detect that it is recent enough to support this behaviour and then
enables passing the architecture extensions to the assembler when this
is the case.

Although the assembly output generated by GCC does not rely on this,
this should ease some issues when using GCC as a driver for compiling
source written directly in assembly language when the programmer was
expecting the appropriate options to be passed on the command line.

gcc/ChangeLog:

	* configure.ac: Detect when the assembler supports new-style
	architecture extensions.
	* common/config/arm/arm-common.c (arm_rewrite_mcpu): Return
	the full CPU string if the assembler can grok it.
	(arm_rewrite_march): Likewise but for the architecture.
	* config.in: Regenerate.
	* configure: Regenerate.

4 files changed, 62 insertions, 0 deletions

diff --git a/gcc/common/config/arm/arm-common.c b/gcc/common/config/arm/arm-common.c
index 481aa9e..de898a7 100644
--- a/gcc/common/config/arm/arm-common.c
+++ b/gcc/common/config/arm/arm-common.c
@@ -115,7 +115,12 @@ const char *
 arm_rewrite_mcpu (int argc, const char **argv)
 {
   gcc_assert (argc);
+
+#ifdef HAVE_GAS_ARM_EXTENDED_ARCH
+  return argv[argc - 1];
+#else
   return arm_rewrite_selected_cpu (argv[argc - 1]);
+#endif
 }
 
 /* Comparator for arm_rewrite_selected_arch.  Compare the two arch extension
@@ -223,7 +228,12 @@ const char *
 arm_rewrite_march (int argc, const char **argv)
 {
   gcc_assert (argc);
+
+#ifdef HAVE_GAS_ARM_EXTENDED_ARCH
+  return argv[argc - 1];
+#else
   return arm_rewrite_selected_arch (argv[argc - 1]);
+#endif
 }
 
 #include "arm-cpu-cdata.h"
diff --git a/gcc/config.in b/gcc/config.in
index d8a810b..61cafe4 100644
--- a/gcc/config.in
+++ b/gcc/config.in
@@ -1331,6 +1331,13 @@
 #endif
 
 
+/* Define if your Arm assembler permits context-specific feature extensions.
+   */
+#ifndef USED_FOR_TARGET
+#undef HAVE_GAS_ARM_EXTENDED_ARCH
+#endif
+
+
 /* Define if your assembler supports .balign and .p2align. */
 #ifndef USED_FOR_TARGET
 #undef HAVE_GAS_BALIGN_AND_P2ALIGN
diff --git a/gcc/configure b/gcc/configure
index 36dba4e..b3de170 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -28881,6 +28881,41 @@ $as_echo "#define HAVE_GCN_SRAM_ECC_GFX908 1" >>confdefs.h
 fi
 
     ;;
+  arm*)
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking assembler for assembler for arm accepts context-specific architecture extensions" >&5
+$as_echo_n "checking assembler for assembler for arm accepts context-specific architecture extensions... " >&6; }
+if ${gcc_cv_as_arm_option_extensions+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  gcc_cv_as_arm_option_extensions=no
+  if test x$gcc_cv_as != x; then
+    $as_echo '.text
+	.thumb
+	.syntax unified
+	vmov.f32 s0, s1' > conftest.s
+    if { ac_try='$gcc_cv_as $gcc_cv_as_flags -march=armv8.1-m.main+mve -o conftest.o conftest.s >&5'
+  { { eval echo "\"\$as_me\":${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_arm_option_extensions=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: $gcc_cv_as_arm_option_extensions" >&5
+$as_echo "$gcc_cv_as_arm_option_extensions" >&6; }
+if test $gcc_cv_as_arm_option_extensions = yes; then
+
+$as_echo "#define HAVE_GAS_ARM_EXTENDED_ARCH 1" >>confdefs.h
+
+fi
+
 esac
 
 # ??? Not all targets support dwarf2 debug_line, even within a version
diff --git a/gcc/configure.ac b/gcc/configure.ac
index fadd34d..7d3aab4 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -5357,6 +5357,16 @@ case "$target" in
       [AC_DEFINE(HAVE_GCN_SRAM_ECC_GFX908, 1,
        [Define if your assembler allows -mattr=+sram-ecc for gfx908.])])
     ;;
+  arm*)
+    gcc_GAS_CHECK_FEATURE([assembler for arm accepts context-specific architecture extensions],
+      gcc_cv_as_arm_option_extensions,
+      [-march=armv8.1-m.main+mve],
+      [.text
+	.thumb
+	.syntax unified
+	vmov.f32 s0, s1],,
+      [AC_DEFINE(HAVE_GAS_ARM_EXTENDED_ARCH, 1,
+       [Define if your Arm assembler permits context-specific feature extensions.])])
 esac
 
 # ??? Not all targets support dwarf2 debug_line, even within a version