Enable -mpcrel on PowerPC -mcpu=future ELF v2 systems, V3
This patch changes the default for -mcpu=future to be -mpcrel (i.e. use
PC-relative addressing) if the ABI allows PC-relative relocations and the user
did not use either -mno-pcrel or -mno-prefixed.
I have changed the spelling of the macro to PCREL_SUPPORTED_BY_ABI (from
PCREL_SUPPORTED_BY_OS) since you pointed out it is more properly a function of
the particular ABI, rather than just an OS choice. I have changed the various
comments to make it clearer.
I have done a bootstrap and a make check with and without the patch and there
were no regressions by adding the patch on a little endian PowerPC Linux
system.
I also tested by hand that if I use:
-mcpu=power9
-mcpu=future -mno-prefixed
-mcpu=future -mno-pcrel
-mcpu=future -mabi=elfv1 (or)
-mcpu=future -mcmodel=large
that PC-relative addressing is not enabled by default. Variants of this patch
have been used since December, building power8/power9 code on big endian
systems, and power8/power9/future on little endian systems. Can I check this
into the master branch?
2020-04-02 Michael Meissner <meiss...@linux.ibm.com>
* config/rs6000/linux64.h (PCREL_SUPPORTED_BY_ABI): Enable
prefixed PC-relative addressing if the ABI supports it.
* config/rs6000/rs6000-cpus.def (ISA_FUTURE_MASKS_SERVER): Do not
set OPTION_MASK_FUTURE here.
* config/rs6000/rs6000.c (rs6000_option_override_internal): Enable
OPTION_MASK_PREFIXED and OPTION_MASK_PREFIXED on -mcpu=future by
default if the current ABI allows the options.
--- /tmp/IPB30g_linux64.h 2020-04-02 15:23:19.977060411 -0500
+++ gcc/config/rs6000/linux64.h 2020-04-02 15:23:01.016474023 -0500
@@ -640,3 +640,11 @@ 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. */
+#undef PCREL_SUPPORTED_BY_ABI
+#define PCREL_SUPPORTED_BY_ABI (TARGET_FUTURE && TARGET_PREFIXED \
+ && ELFv2_ABI_CHECK \
+ && (TARGET_CMODEL == CMODEL_MEDIUM))
--- /tmp/EHqpAk_rs6000-cpus.def 2020-04-02 15:23:19.993064282 -0500
+++ gcc/config/rs6000/rs6000-cpus.def 2020-04-02 15:23:01.016474023 -0500
@@ -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 the addressing
+ options OPTION_MASK_PREFIXED or OPTION_MASK_PCREL here. Those options are
+ enabled in the function rs6000_option_override if the ABI supports them. */
#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/Zayhhc_rs6000.c 2020-04-02 15:23:20.009068153 -0500
+++ gcc/config/rs6000/rs6000.c 2020-04-02 15:23:01.020474991 -0500
@@ -4020,6 +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)
{
@@ -4181,6 +4186,14 @@ rs6000_option_override_internal (bool gl
rs6000_isa_flags &= ~OPTION_MASK_PCREL;
}
+#ifdef PCREL_SUPPORTED_BY_ABI
+ /* If the ABI has support for PC-relative relocations, enable it by
+ default. */
+ if (PCREL_SUPPORTED_BY_ABI
+ && (rs6000_isa_flags_explicit & OPTION_MASK_PCREL) == 0)
+ rs6000_isa_flags |= OPTION_MASK_PCREL;
+#endif
+
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: meiss...@linux.ibm.com, phone: +1 (978) 899-4797
