MIPS: Not trigger error for pre-R6 and -mcompact-branches=always

For MIPSr6, we may wish to use compact-branches only.
Currently, we have to use `always' option, while it is mark as conflict
with pre-R6.
  cc1: error: unsupported combination: ‘mips32r2’ -mcompact-branches=always
Just ignore -mcompact-branches=always for pre-R6.

This patch also defines
    __mips_compact_branches_never
    __mips_compact_branches_always
    __mips_compact_branches_optimal
predefined macros

gcc/ChangeLog:
	* config/mips/mips.cc (mips_option_override): not trigger error
	for compact-branches=always for pre-R6.
	* config/mips/mips.h (TARGET_RTP_PIC): not trigger error for
	compact-branches=always for pre-R6.
	(TARGET_CB_NEVER): Likewise.
	(TARGET_CB_ALWAYS): Likewise.
	(struct mips_cpu_info): define macros for compact branch policy.
	* doc/invoke.texi: Document "always" with pre-R6.

gcc/testsuite/ChangeLog:
	* gcc.target/mips/compact-branches-1.c: add isa_rev>=6.
	* gcc.target/mips/mips.exp: don't add -mipsXXr6 option for
	-mcompact-branches=always. It is usable for pre-R6 now.
	* gcc.target/mips/compact-branches-8.c: New test.
	* gcc.target/mips/compact-branches-9.c: New test.

2 files changed, 15 insertions, 15 deletions

diff --git a/gcc/config/mips/mips.cc b/gcc/config/mips/mips.cc
index 387376b..699ea6c 100644
--- a/gcc/config/mips/mips.cc
+++ b/gcc/config/mips/mips.cc
@@ -20277,13 +20277,7 @@ mips_option_override (void)
       target_flags |= MASK_ODD_SPREG;
     }
 
-  if (!ISA_HAS_COMPACT_BRANCHES && mips_cb == MIPS_CB_ALWAYS)
-    {
-      error ("unsupported combination: %qs%s %s",
-	      mips_arch_info->name, TARGET_MICROMIPS ? " -mmicromips" : "",
-	      "-mcompact-branches=always");
-    }
-  else if (!ISA_HAS_DELAY_SLOTS && mips_cb == MIPS_CB_NEVER)
+  if (!ISA_HAS_DELAY_SLOTS && mips_cb == MIPS_CB_NEVER)
     {
       error ("unsupported combination: %qs%s %s",
 	      mips_arch_info->name, TARGET_MICROMIPS ? " -mmicromips" : "",
diff --git a/gcc/config/mips/mips.h b/gcc/config/mips/mips.h
index fe7f5b2..ed058b5 100644
--- a/gcc/config/mips/mips.h
+++ b/gcc/config/mips/mips.h
@@ -120,11 +120,9 @@ struct mips_cpu_info {
 #define TARGET_RTP_PIC (TARGET_VXWORKS_RTP && flag_pic)
 
 /* Compact branches must not be used if the user either selects the
-   'never' policy or the 'optimal' policy on a core that lacks
+   'never' policy or the 'optimal' / 'always' policy on a core that lacks
    compact branch instructions.  */
-#define TARGET_CB_NEVER (mips_cb == MIPS_CB_NEVER	\
-			 || (mips_cb == MIPS_CB_OPTIMAL \
-			     && !ISA_HAS_COMPACT_BRANCHES))
+#define TARGET_CB_NEVER (mips_cb == MIPS_CB_NEVER || !ISA_HAS_COMPACT_BRANCHES)
 
 /* Compact branches may be used if the user either selects the
    'always' policy or the 'optimal' policy on a core that supports
@@ -134,10 +132,11 @@ struct mips_cpu_info {
 			     && ISA_HAS_COMPACT_BRANCHES))
 
 /* Compact branches must always be generated if the user selects
-   the 'always' policy or the 'optimal' policy om a core that
-   lacks delay slot branch instructions.  */
-#define TARGET_CB_ALWAYS (mips_cb == MIPS_CB_ALWAYS	\
-			 || (mips_cb == MIPS_CB_OPTIMAL \
+   the 'always' policy on a core support compact branches,
+   or the 'optimal' policy on a core that lacks delay slot branch instructions.  */
+#define TARGET_CB_ALWAYS ((mips_cb == MIPS_CB_ALWAYS	  \
+			     && ISA_HAS_COMPACT_BRANCHES) \
+			 || (mips_cb == MIPS_CB_OPTIMAL   \
 			     && !ISA_HAS_DELAY_SLOTS))
 
 /* Special handling for JRC that exists in microMIPSR3 as well as R6
@@ -677,6 +676,13 @@ struct mips_cpu_info {
 	builtin_define ("__mips_no_lxc1_sxc1");				\
       if (!ISA_HAS_UNFUSED_MADD4 && !ISA_HAS_FUSED_MADD4)		\
 	builtin_define ("__mips_no_madd4");				\
+									\
+      if (TARGET_CB_NEVER)						\
+	builtin_define ("__mips_compact_branches_never");		\
+      else if (TARGET_CB_ALWAYS)					\
+	builtin_define ("__mips_compact_branches_always");		\
+      else 								\
+	builtin_define ("__mips_compact_branches_optimal");		\
     }									\
   while (0)