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.

7 files changed, 43 insertions, 23 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)
 
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index d49c137..64f77e8 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -27091,11 +27091,13 @@ The @option{-mcompact-branches=never} option ensures that compact branch
 instructions will never be generated.
 
 The @option{-mcompact-branches=always} option ensures that a compact
-branch instruction will be generated if available.  If a compact branch
-instruction is not available, a delay slot form of the branch will be
-used instead.
+branch instruction will be generated if available for MIPS Release 6 onwards.
+If a compact branch instruction is not available (or pre-R6),
+a delay slot form of the branch will be used instead.
 
-This option is supported from MIPS Release 6 onwards.
+If it is used for MIPS16/microMIPS targets, it will be just ignored now.
+The behaviour for MIPS16/microMIPS may change in future,
+since they do have some compact branch instructions.
 
 The @option{-mcompact-branches=optimal} option will cause a delay slot
 branch to be used if one is available in the current ISA and the delay
diff --git a/gcc/testsuite/gcc.target/mips/compact-branches-1.c b/gcc/testsuite/gcc.target/mips/compact-branches-1.c
index 9c7365e..6b8e197 100644
--- a/gcc/testsuite/gcc.target/mips/compact-branches-1.c
+++ b/gcc/testsuite/gcc.target/mips/compact-branches-1.c
@@ -1,4 +1,4 @@
-/* { dg-options "-mcompact-branches=always -mno-micromips" } */
+/* { dg-options "-mcompact-branches=always -mno-micromips isa_rev>=6" } */
 int glob;
 
 void
diff --git a/gcc/testsuite/gcc.target/mips/compact-branches-8.c b/gcc/testsuite/gcc.target/mips/compact-branches-8.c
new file mode 100644
index 0000000..1290ced
--- /dev/null
+++ b/gcc/testsuite/gcc.target/mips/compact-branches-8.c
@@ -0,0 +1,10 @@
+/* { dg-options "-mno-abicalls -mcompact-branches=always isa_rev<=5" } */
+void bar (int);
+
+void
+foo ()
+{
+  bar (1);
+}
+
+/* { dg-final { scan-assembler "\t(j|jal)\t" } } */
diff --git a/gcc/testsuite/gcc.target/mips/compact-branches-9.c b/gcc/testsuite/gcc.target/mips/compact-branches-9.c
new file mode 100644
index 0000000..4b23bf4
--- /dev/null
+++ b/gcc/testsuite/gcc.target/mips/compact-branches-9.c
@@ -0,0 +1,10 @@
+/* { dg-options "-mno-abicalls -fno-PIC -mcompact-branches=always isa_rev>=6" } */
+void bar (int);
+
+void
+foo ()
+{
+  bar (1);
+}
+
+/* { dg-final { scan-assembler "\t(bc|balc)\t" } } */
diff --git a/gcc/testsuite/gcc.target/mips/mips.exp b/gcc/testsuite/gcc.target/mips/mips.exp
index 42a0dbb..c89626a 100644
--- a/gcc/testsuite/gcc.target/mips/mips.exp
+++ b/gcc/testsuite/gcc.target/mips/mips.exp
@@ -1167,10 +1167,8 @@ proc mips-dg-options { args } {
 	# We need a revision 6 or better ISA for:
 	#
 	#   - When the LSA instruction is required
-	#   - When only using compact branches
 	if { $isa_rev < 6
-	     && ([mips_have_test_option_p options "HAS_LSA"]
-		 || [mips_have_test_option_p options "-mcompact-branches=always"]) } {
+	     && ([mips_have_test_option_p options "HAS_LSA"]) } {
 	    if { $gp_size == 32 } {
 		mips_make_test_option options "-mips32r6"
 	    } else {