Turn on -mpcrel by default for -mcpu=future

2020-04-25  Michael Meissner  <meissner@linux.ibm.com>

	* config/rs6000/linux64.h (PCREL_SUPPORTED_BY_OS): Define to
	enable PC-relative addressing for -mcpu=future.
	* config/rs6000/rs6000-cpus.def (ISA_FUTURE_MASKS_SERVER): Move
	after OTHER_FUTURE_MASKS.  Use OTHER_FUTURE_MASKS.
	* config/rs6000/rs6000.c (PCREL_SUPPORTED_BY_OS): If not defined,
	suppress PC-relative addressing.
	(rs6000_option_override_internal): Split up error messages
	checking for -mprefixed and -mpcrel.  Enable -mpcrel if the target
	system supports it.

gcc/ChangeLog

+2020-04-25  Michael Meissner  <meissner@linux.ibm.com>
+
+	* config/rs6000/linux64.h (PCREL_SUPPORTED_BY_OS): Define to
+	enable PC-relative addressing for -mcpu=future.
+	* config/rs6000/rs6000-cpus.def (ISA_FUTURE_MASKS_SERVER): Move
+	after OTHER_FUTURE_MASKS.  Use OTHER_FUTURE_MASKS.
+	* config/rs6000/rs6000.c (PCREL_SUPPORTED_BY_OS): If not defined,
+	suppress PC-relative addressing.
+	(rs6000_option_override_internal): Split up error messages
+	checking for -mprefixed and -mpcrel.  Enable -mpcrel if the target
+	system supports it.
+
 2020-04-25  Jakub Jelinek  <jakub@redhat.com>
 	    Richard Biener  <rguenther@suse.de>
 

gcc/config/rs6000/linux64.h

@@ -640,3 +640,10 @@ extern int dot_symbols;
    enabling the __float128 keyword.  */
 #undef	TARGET_FLOAT128_ENABLE_TYPE
 #define TARGET_FLOAT128_ENABLE_TYPE 1
+
+/* Enable using prefixed PC-relative addressing on the 'future' machine if the
+   ABI supports it.  The ELF v2 ABI only supports PC-relative relocations for
+   the medium code model.  */
+#define PCREL_SUPPORTED_BY_OS	(TARGET_FUTURE && TARGET_PREFIXED	\
+				 && ELFv2_ABI_CHECK			\
+				 && TARGET_CMODEL == CMODEL_MEDIUM)

gcc/config/rs6000/rs6000-cpus.def

@@ -75,16 +75,15 @@
 				 | OPTION_MASK_P8_VECTOR		\
 				 | OPTION_MASK_P9_VECTOR)
 
-/* Support for a future processor's features.  Do not enable -mpcrel until it
-   is fully functional.  */
-#define ISA_FUTURE_MASKS_SERVER	(ISA_3_0_MASKS_SERVER			\
-				 | OPTION_MASK_FUTURE			\
-				 | OPTION_MASK_PREFIXED)
-
 /* Flags that need to be turned off if -mno-future.  */
 #define OTHER_FUTURE_MASKS	(OPTION_MASK_PCREL			\
 				 | OPTION_MASK_PREFIXED)
 
+/* Support for a future processor's features.  */
+#define ISA_FUTURE_MASKS_SERVER	(ISA_3_0_MASKS_SERVER			\
+				 | OPTION_MASK_FUTURE			\
+				 | OTHER_FUTURE_MASKS)
+
 /* Flags that need to be turned off if -mno-power9-vector.  */
 #define OTHER_P9_VECTOR_MASKS	(OPTION_MASK_FLOAT128_HW		\
 				 | OPTION_MASK_P9_MINMAX)

gcc/config/rs6000/rs6000.c

@@ -98,6 +98,11 @@
 #endif
 #endif
 
+/* Don't enable PC-relative addressing if the target does not support it.  */
+#ifndef PCREL_SUPPORTED_BY_OS
+#define PCREL_SUPPORTED_BY_OS	0
+#endif
+
 /* Support targetm.vectorize.builtin_mask_for_load.  */
 tree altivec_builtin_mask_for_load;
 
@@ -4024,15 +4029,17 @@ rs6000_option_override_internal (bool global_init_p)
       rs6000_isa_flags &= ~OPTION_MASK_FLOAT128_HW;
     }
 
-  /* -mprefixed (and hence -mpcrel) requires -mcpu=future.  */
-  if (TARGET_PREFIXED && !TARGET_FUTURE)
+  /* Enable -mprefixed by default on 'future' systems.  */
+  if (TARGET_FUTURE && (rs6000_isa_flags_explicit & OPTION_MASK_PREFIXED) == 0)
+    rs6000_isa_flags |= OPTION_MASK_PREFIXED;
+
+  /* -mprefixed requires -mcpu=future.  */
+  else if (TARGET_PREFIXED && !TARGET_FUTURE)
     {
-      if ((rs6000_isa_flags_explicit & OPTION_MASK_PCREL) != 0)
-	error ("%qs requires %qs", "-mpcrel", "-mcpu=future");
-      else if ((rs6000_isa_flags_explicit & OPTION_MASK_PREFIXED) != 0)
+      if ((rs6000_isa_flags_explicit & OPTION_MASK_PREFIXED) != 0)
 	error ("%qs requires %qs", "-mprefixed", "-mcpu=future");
 
-      rs6000_isa_flags &= ~(OPTION_MASK_PCREL | OPTION_MASK_PREFIXED);
+      rs6000_isa_flags &= ~OPTION_MASK_PREFIXED;
     }
 
   /* -mpcrel requires prefixed load/store addressing.  */
@@ -4175,9 +4182,16 @@ rs6000_option_override_internal (bool global_init_p)
   SUB3TARGET_OVERRIDE_OPTIONS;
 #endif
 
+  /* If the ABI has support for PC-relative relocations, enable it by default.
+     This test depends on the sub-target tests above setting the code model to
+     medium for ELF v2 systems.  */
+  if (PCREL_SUPPORTED_BY_OS
+      && (rs6000_isa_flags_explicit & OPTION_MASK_PCREL) == 0)
+    rs6000_isa_flags |= OPTION_MASK_PCREL;
+
   /* -mpcrel requires -mcmodel=medium, but we can't check TARGET_CMODEL until
       after the subtarget override options are done.  */
-  if (TARGET_PCREL && TARGET_CMODEL != CMODEL_MEDIUM)
+  else if (TARGET_PCREL && TARGET_CMODEL != CMODEL_MEDIUM)
     {
       if ((rs6000_isa_flags_explicit & OPTION_MASK_PCREL) != 0)
 	error ("%qs requires %qs", "-mpcrel", "-mcmodel=medium");