arm: Ignore --with-mode when CPU only supports one instruction set.

Arm processors can support up to two instruction sets.  Some early
cores only support the traditional A32 (Arm) instructions, while some
more recent devices only support T32 (Thumb) instructions.

When configuring the compiler,--with-mode can be used to select the
default instruction set to target if the user has not made an explicit
choice, but this can cause needless problems if the default is not
supported by the requested CPU.

To fix this this patch adjusts the way that the --with-mode selection
is processed so that it can take into account the selected CPU or
architecture and not create a meaningless combination.

gcc:
	* common/config/arm/arm-common.c: Include configargs.h.
	(arm_config_default): New function.
	(arm_target_mode): Renamed from arm_target_thumb_only.  Handle
	processors that do not support Thumb.  Take into account the
	--with-mode configuration setting for selecting the default.
	* config/arm/arm.h (OPTION_DEFAULT_SPECS): Remove entry for 'mode'.
	(TARGET_MODE_SPEC_FUNCTIONS): Update for function name change.

1 files changed, 43 insertions, 6 deletions

diff --git a/gcc/common/config/arm/arm-common.c b/gcc/common/config/arm/arm-common.c
index 98824517c7b..5b03b86724d 100644
--- a/gcc/common/config/arm/arm-common.c
+++ b/gcc/common/config/arm/arm-common.c
@@ -33,6 +33,8 @@
 #include "sbitmap.h"
 #include "diagnostic.h"
 
+#include "configargs.h"
+
 /* Set default optimization options.  */
 static const struct default_options arm_option_optimization_table[] =
   {
@@ -240,16 +242,34 @@ check_isa_bits_for (const enum isa_feature* bits, enum isa_feature bit)
   return false;
 }
 
+/* Look up NAME in the configuration defaults for this build of the
+   the compiler.  Return the value associated with that name, or NULL
+   if no value is found.  */
+static const char *
+arm_config_default (const char *name)
+{
+  int i;
+
+  if (configure_default_options[0].name == NULL)
+    return NULL;
+
+  for (i = 0; i < ARRAY_SIZE (configure_default_options); i++)
+    if (strcmp (configure_default_options[i].name, name) == 0)
+      return configure_default_options[i].value;
+
+  return NULL;
+}
+
 /* Called by the driver to check whether the target denoted by current
-   command line options is a Thumb-only target.  ARGV is an array of
-   tupples (normally only one) where the first element of the tupple
-   is 'cpu' or 'arch' and the second is the option passed to the
-   compiler for that.  An architecture tupple is always taken in
-   preference to a cpu tupple and the last of each type always
+   command line options is a Thumb-only, or ARM-only, target.  ARGV is
+   an array of tupples (normally only one) where the first element of
+   the tupple is 'cpu' or 'arch' and the second is the option passed
+   to the compiler for that.  An architecture tupple is always taken
+   in preference to a cpu tupple and the last of each type always
    overrides any earlier setting.  */
 
 const char *
-arm_target_thumb_only (int argc, const char **argv)
+arm_target_mode (int argc, const char **argv)
 {
   const char *arch = NULL;
   const char *cpu = NULL;
@@ -285,6 +305,9 @@ arm_target_thumb_only (int argc, const char **argv)
       if (arch_opt && !check_isa_bits_for (arch_opt->common.isa_bits,
 					   isa_bit_notm))
 	return "-mthumb";
+      if (arch_opt && !check_isa_bits_for (arch_opt->common.isa_bits,
+					   isa_bit_thumb))
+	return "-marm";
     }
   else if (cpu)
     {
@@ -294,6 +317,20 @@ arm_target_thumb_only (int argc, const char **argv)
       if (cpu_opt && !check_isa_bits_for (cpu_opt->common.isa_bits,
 					  isa_bit_notm))
 	return "-mthumb";
+      if (cpu_opt && !check_isa_bits_for (cpu_opt->common.isa_bits,
+					   isa_bit_thumb))
+	return "-marm";
+    }
+
+  const char *default_mode = arm_config_default ("mode");
+  if (default_mode)
+    {
+      if (strcmp (default_mode, "thumb") == 0)
+	return "-mthumb";
+      else if (strcmp (default_mode, "arm") == 0)
+	return "-marm";
+      else
+	gcc_unreachable ();
     }
 
   /* Compiler hasn't been configured with a default, and the CPU