[PATCH], Make PowerPC -mcpu=future enable -mpcrel on linux ELFv2

[Michael Meissner <meissner@linux.ibm.com>]

This is a revised version of the patch I posted on March 23rd.  The changes are
to update the comments and improve the ChangeLog.

There were no regressions when I did the bootstrap and make check steps.  I
verified that -mcpu=future does turn on -mprecl if you are targeting a Linux
ELF v2 system and use the medium code model.  Can I check this into the master
branch?

2020-03-27  Michael Meissner  <meissner@linux.ibm.com>

	* config/rs6000/linux64.h (PCREL_SUPPORTED_BY_OS): New macro.
	* config/rs6000/rs6000-cpus.def (ISA_FUTURE_MASKS_SERVER): Do not
	set -mprefixed here.
	* config/rs6000/rs6000.c (PCREL_SUPPORTED_BY_OS): New macro.
	(rs6000_option_override_internal): Set the -mprefixed and -mpcrel
	options for -mcpu=future if these options can be used.

--- /tmp/JVBhAf_linux64.h	2020-03-27 16:27:05.478619500 -0400
+++ gcc/config/rs6000/linux64.h	2020-03-27 16:21:56.268876616 -0400
@@ -640,3 +640,11 @@ extern int dot_symbols;
    enabling the __float128 keyword.  */
 #undef	TARGET_FLOAT128_ENABLE_TYPE
 #define TARGET_FLOAT128_ENABLE_TYPE 1
+
+/* Enable default support for PC-relative addressing on the 'future' system if
+   we can use the PC-relative instructions.  Currently this support only exits
+   for the ELF v2 object file format using the medium code model.  */
+#undef  PCREL_SUPPORTED_BY_OS
+#define PCREL_SUPPORTED_BY_OS	(TARGET_FUTURE && TARGET_PREFIXED	\
+				 && ELFv2_ABI_CHECK			\
+				 && (TARGET_CMODEL == CMODEL_MEDIUM))
--- /tmp/KyQOUN_rs6000-cpus.def	2020-03-27 16:27:05.488619427 -0400
+++ gcc/config/rs6000/rs6000-cpus.def	2020-03-27 16:23:51.780030238 -0400
@@ -75,11 +75,11 @@
 				 | OPTION_MASK_P8_VECTOR		\
 				 | OPTION_MASK_P9_VECTOR)
 
-/* Support for a future processor's features.  Do not enable -mpcrel until it
-   is fully functional.  */
+/* Support for a future processor's features.  We do not set -mpcrel or
+   -mprefixed here.  These bits are set in rs6000_option_override if the system
+   supports those options. */
 #define ISA_FUTURE_MASKS_SERVER	(ISA_3_0_MASKS_SERVER			\
-				 | OPTION_MASK_FUTURE			\
-				 | OPTION_MASK_PREFIXED)
+				 | OPTION_MASK_FUTURE)
 
 /* Flags that need to be turned off if -mno-future.  */
 #define OTHER_FUTURE_MASKS	(OPTION_MASK_PCREL			\
--- /tmp/z4Mwhm_rs6000.c	2020-03-27 16:27:05.500619340 -0400
+++ gcc/config/rs6000/rs6000.c	2020-03-27 16:20:13.066641659 -0400
@@ -98,6 +98,12 @@
 #endif
 #endif
 
+/* Set up the defaults for whether PC-relative addressing is supported by the
+   target system.  */
+#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;
 
@@ -4014,6 +4020,11 @@ rs6000_option_override_internal (bool gl
       rs6000_isa_flags &= ~OPTION_MASK_FLOAT128_HW;
     }
 
+  /* Enable -mprefixed by default on 64-bit 'future' systems.  */
+  if (TARGET_FUTURE && TARGET_POWERPC64
+      && (rs6000_isa_flags_explicit & OPTION_MASK_PREFIXED) == 0)
+    rs6000_isa_flags |= OPTION_MASK_PREFIXED;
+
   /* -mprefixed (and hence -mpcrel) requires -mcpu=future.  */
   if (TARGET_PREFIXED && !TARGET_FUTURE)
     {
@@ -4175,6 +4186,11 @@ rs6000_option_override_internal (bool gl
       rs6000_isa_flags &= ~OPTION_MASK_PCREL;
     }
 
+  /* If the OS has support for PC-relative relocations, enable it now.  */
+  if (PCREL_SUPPORTED_BY_OS
+      && (rs6000_isa_flags_explicit & OPTION_MASK_PCREL) == 0)
+    rs6000_isa_flags |= OPTION_MASK_PCREL;
+
   if (TARGET_DEBUG_REG || TARGET_DEBUG_TARGET)
     rs6000_print_isa_options (stderr, 0, "after subtarget", rs6000_isa_flags);
 


-- 
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA
email: meissner@linux.ibm.com, phone: +1 (978) 899-4797