[PATCH, V3, #5 of 10], Make -mpcrel default on little endian Linux systems

[Michael Meissner <meissner at linux dot ibm dot com>]

I rewrote the simple previous patch (V1 #5) to enable pc-relative addressing by
default, to only enable by default on little endian Linux systems.  Other
systems like AIX and BSD will default to not supporting prefixed addressing
until they are configured to support these addressing modes.

I added checks for 32-bit, ELF v1, and reworked the checks for small/large code
model.  The check is now done in one place.

I built a bootstrap compiler on a little endian power8 system and there were no
regressions in running make check.

In addition, I built cross compilers on my Linux x86_64 system, and checked
that even on Linux 64-bit little endian systems, you can disable the default
behavior by defining TARGET_PREFIXED_ADDR_DEFAULT and TARGET_PCREL_DEFAULT to 0
(the first disables both prefixed addressing with numeric offsets and
pc-relative addressing, while the second disables pc-relative addressing).

I built a bootstrap compiler on a little endian power8 system, and there were
no regressions in make check.  Can I check this into the trunk once the
previous patches are checked in?

2019-08-26  Michael Meissner  <meissner@linux.ibm.com>

	* config/rs6000/linux64.h (TARGET_PREFIXED_ADDR_DEFAULT): On
	'future' systems, enable prefixed addressing by default.
	(TARGET_PCREL_DEFAULT): On 'future' systems, enable pc-relative
	addressing by default.
	* config/rs6000/rs6000-cpus.def (FUTURE_ADDRESS_MASKS): New macro
	of 'future' addressing masks.
	(OTHER_FUTURE_MASKS): Use FUTURE_ADDRESS_MASKS.
	* config/rs6000/rs6000.c (TARGET_PREFIXED_ADDR_DEFAULT): If not
	defined, don't enable prefixed addressing on 'future' systems.
	(TARGET_PCREL_DEFAULT): If not defined, don't enable pc-relative
	addressing on 'future' systems.
	(rs6000_debug_reg_global): Print TARGET_PREFIXED_ADDR_DEFAULT and
	TARGET_PCREL_DEFAULT.
	(rs6000_option_override_internal): Add checks for 32-bit systems
	and non ELFv2 systems trying to enable prefixed addressing.  If
	the target OS tm.h says it is safe to do, enable prefixed and
	pc-relative addressing.

Index: gcc/config/rs6000/linux64.h
===================================================================
--- gcc/config/rs6000/linux64.h	(revision 274864)
+++ gcc/config/rs6000/linux64.h	(working copy)
@@ -640,3 +640,13 @@ extern int dot_symbols;
    enabling the __float128 keyword.  */
 #undef	TARGET_FLOAT128_ENABLE_TYPE
 #define TARGET_FLOAT128_ENABLE_TYPE 1
+
+/* By default enable support for pc-relative and numeric prefixed addressing on
+   the 'future' system, unless it is overriden at build time.  */
+#ifndef TARGET_PREFIXED_ADDR_DEFAULT
+#define TARGET_PREFIXED_ADDR_DEFAULT	1
+#endif
+
+#if !defined (TARGET_PCREL_DEFAULT) && TARGET_PREFIXED_ADDR_DEFAULT
+#define TARGET_PCREL_DEFAULT		1
+#endif
Index: gcc/config/rs6000/rs6000-cpus.def
===================================================================
--- gcc/config/rs6000/rs6000-cpus.def	(revision 274864)
+++ gcc/config/rs6000/rs6000-cpus.def	(working copy)
@@ -75,15 +75,21 @@
 				 | 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.  The prefixed and pc-relative
+   addressing bits are not added here.  Instead, rs6000.c adds them if the OS
+   tm.h says that it supports the addressing modes.  */
 #define ISA_FUTURE_MASKS_SERVER	(ISA_3_0_MASKS_SERVER			\
-				 | OPTION_MASK_FUTURE			\
+				 | OPTION_MASK_FUTURE)
+
+/* Addressing related flags on a future processor.  These flags are broken out
+   because not all targets will support either pc-relative addressing, or even
+   prefixed addressing, and we want to clear all of the addressing bits
+   on targets that cannot support prefixed/pcrel addressing.  */
+#define ADDRESSING_FUTURE_MASKS	(OPTION_MASK_PCREL			\
 				 | OPTION_MASK_PREFIXED_ADDR)
 
 /* Flags that need to be turned off if -mno-future.  */
-#define OTHER_FUTURE_MASKS	(OPTION_MASK_PCREL			\
-				 | OPTION_MASK_PREFIXED_ADDR)
+#define OTHER_FUTURE_MASKS	ADDRESSING_FUTURE_MASKS
 
 /* Flags that need to be turned off if -mno-power9-vector.  */
 #define OTHER_P9_VECTOR_MASKS	(OPTION_MASK_FLOAT128_HW		\
Index: gcc/config/rs6000/rs6000.c
===================================================================
--- gcc/config/rs6000/rs6000.c	(revision 274874)
+++ gcc/config/rs6000/rs6000.c	(working copy)
@@ -98,6 +98,16 @@
 #endif
 #endif
 
+/* Set up the defaults for whether prefixed addressing is used, and if it is
+   used, whether we want to turn on pc-relative support by default.  */
+#ifndef TARGET_PREFIXED_ADDR_DEFAULT
+#define TARGET_PREFIXED_ADDR_DEFAULT	0
+#endif
+
+#ifndef TARGET_PCREL_DEFAULT
+#define TARGET_PCREL_DEFAULT		0
+#endif
+
 /* Support targetm.vectorize.builtin_mask_for_load.  */
 GTY(()) tree altivec_builtin_mask_for_load;
 
@@ -2523,6 +2533,14 @@ rs6000_debug_reg_global (void)
   if (TARGET_DIRECT_MOVE_128)
     fprintf (stderr, DEBUG_FMT_D, "VSX easy 64-bit mfvsrld element",
 	     (int)VECTOR_ELEMENT_MFVSRLD_64BIT);
+
+  if (TARGET_FUTURE)
+    {
+      fprintf (stderr, DEBUG_FMT_D, "TARGET_PREFIXED_ADDR_DEFAULT",
+	       TARGET_PREFIXED_ADDR_DEFAULT);
+      fprintf (stderr, DEBUG_FMT_D, "TARGET_PCREL_DEFAULT",
+	       TARGET_PCREL_DEFAULT);
+    }
 }
 
 
@@ -4217,26 +4235,6 @@ rs6000_option_override_internal (bool gl
       rs6000_isa_flags &= ~OPTION_MASK_FLOAT128_HW;
     }
 
-  /* -mprefixed-addr (and hence -mpcrel) requires -mcpu=future.  */
-  if (TARGET_PREFIXED_ADDR && !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_ADDR) != 0)
-	error ("%qs requires %qs", "-mprefixed-addr", "-mcpu=future");
-
-      rs6000_isa_flags &= ~(OPTION_MASK_PCREL | OPTION_MASK_PREFIXED_ADDR);
-    }
-
-  /* -mpcrel requires prefixed load/store addressing.  */
-  if (TARGET_PCREL && !TARGET_PREFIXED_ADDR)
-    {
-      if ((rs6000_isa_flags_explicit & OPTION_MASK_PCREL) != 0)
-	error ("%qs requires %qs", "-mpcrel", "-mprefixed-addr");
-
-      rs6000_isa_flags &= ~OPTION_MASK_PCREL;
-    }
-
   /* Print the options after updating the defaults.  */
   if (TARGET_DEBUG_REG || TARGET_DEBUG_TARGET)
     rs6000_print_isa_options (stderr, 0, "after defaults", rs6000_isa_flags);
@@ -4368,12 +4366,89 @@ rs6000_option_override_internal (bool gl
   SUB3TARGET_OVERRIDE_OPTIONS;
 #endif
 
-  /* -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)
+  /* Enable prefixed addressing and pc-relative addressing on 64-bit ELF v2
+     systems if the OS tm.h file says that it is supported and the user did not
+     explicitly use -mprefixed-addr or -mpcrel.  At the present time, only
+     64-bit Linux enables this.
+
+     Pc-relative support also requires the medium code model.
+
+     However, we can't check for ELFv2 or -mcmodel=medium until after the
+     subtarget macros are run.
+
+     If prefixed addressing is disabled by default, and the user does -mpcrel,
+     don't force them to also specify -mprefixed-addr.  */
+  if (TARGET_FUTURE)
+    {
+      bool explicit_prefixed = ((rs6000_isa_flags_explicit
+				 & OPTION_MASK_PREFIXED_ADDR) != 0);
+      bool explicit_pcrel = ((rs6000_isa_flags_explicit
+			      & OPTION_MASK_PCREL) != 0);
+
+      /* Prefixed addressing requires 64-bit registers.  */
+      if (!TARGET_POWERPC64)
+	{
+	  if (TARGET_PCREL && explicit_pcrel)
+	    error ("%qs requires %qs", "-mpcrel", "-m64");
+
+	  else if (TARGET_PREFIXED_ADDR && explicit_prefixed)
+	    error ("%qs requires %qs", "-mprefixed-addr", "-m64");
+
+	  rs6000_isa_flags &= ~ADDRESSING_FUTURE_MASKS;
+	}
+
+      /* Only ELFv2 currently supports prefixed/pcrel addressing.  */
+      else if (rs6000_current_abi != ABI_ELFv2)
+	{
+	  if (TARGET_PCREL && explicit_pcrel)
+	    error ("%qs requires %qs", "-mpcrel", "-mabi=elfv2");
+
+	  else if (TARGET_PREFIXED_ADDR && explicit_prefixed)
+	    error ("%qs requires %qs", "-mprefixed-addr", "-mabi=elfv2");
+
+	  rs6000_isa_flags &= ~ADDRESSING_FUTURE_MASKS;
+	}
+
+      /* Pc-relative requires the medium code model.  */
+      else if (TARGET_PCREL && TARGET_CMODEL != CMODEL_MEDIUM)
+	{
+	  if ((rs6000_isa_flags_explicit & OPTION_MASK_PCREL) != 0)
+	    error ("%qs requires %qs", "-mpcrel", "-mcmodel=medium");
+
+	  rs6000_isa_flags &= ~OPTION_MASK_PCREL;
+	}
+
+      /* Enable defaults if desired.  */
+      else
+	{
+	  if (!explicit_prefixed
+	      && (TARGET_PREFIXED_ADDR_DEFAULT
+		  || TARGET_PCREL
+		  || TARGET_PCREL_DEFAULT))
+	    rs6000_isa_flags |= OPTION_MASK_PREFIXED_ADDR;
+
+	  if (!explicit_pcrel && TARGET_PCREL_DEFAULT
+	      && TARGET_CMODEL == CMODEL_MEDIUM)
+	    rs6000_isa_flags |= OPTION_MASK_PCREL;
+	}
+    }
+
+  /* -mprefixed-addr (and hence -mpcrel) requires -mcpu=future.  */
+  if (TARGET_PREFIXED_ADDR && !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_ADDR) != 0)
+	error ("%qs requires %qs", "-mprefixed-addr", "-mcpu=future");
+
+      rs6000_isa_flags &= ~(OPTION_MASK_PCREL | OPTION_MASK_PREFIXED_ADDR);
+    }
+
+  /* -mpcrel requires prefixed load/store addressing.  */
+  if (TARGET_PCREL && !TARGET_PREFIXED_ADDR)
     {
       if ((rs6000_isa_flags_explicit & OPTION_MASK_PCREL) != 0)
-	error ("%qs requires %qs", "-mpcrel", "-mcmodel=medium");
+	error ("%qs requires %qs", "-mpcrel", "-mprefixed-addr");
 
       rs6000_isa_flags &= ~OPTION_MASK_PCREL;
     }

-- 
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