On Thu, Oct 16, 2014 at 12:25 PM, Uros Bizjak <ubiz...@gmail.com> wrote:
>>> >> Now that %ebx is also allocatable in PIC modes, we can cleanup
>>> >> config/i386/cpuid considerably. I propose to remove all PIC related
>>> >> specializations of __cpuid and __cpuid_count and protect the
>>> >> compilation with "#if __GNUC__ >= 5".
>>> >>
>>> >> The only drawback would be that non-bootstrapped build with gcc < 5.0
>>> >> will ignore -march=native, but I think this should be acceptable.
>>> >
>>> > I'm worried about that.
>>> > Can't you instead keep the current cpuid.h stuff as is, just add
>>> > && __GNUC__ < 5
>>> > to that, so it treats GCC 5+ PIC as if __PIC__ wasn't defined?
>>> >
>>> > Or, at least use cpuid.h even for older GCC if __PIC__ is not defined
>>> > (or __x86_64__ is defined and not medium/large PIC model)?
>>>
>>> Do we really care that much about non-bootstrapped build? I don't see
>>
>> At least on Linux, driver-i386.c should not be built with PIC normally,
>> so at least changing
>> #if __GNUC__ >= 5
>> to
>> #if defined(__GNUC__) && (__GNUC__ >= 5 || !defined(__PIC__))
>> would limit the -march=native change for non-bootstrapped compilers to
>> Darwin only (or what other targets use PIC by default?).
>
> Yes, this would work for me - the goal is to keep only one "universal"
> __cpuid (and __cpuid_count) define, and the above condition fits this
> goal.
I have committed the attached patch to mainline SVN.
2014-10-17 Uros Bizjak <ubiz...@gmail.com>
* config/i386/cpuid.h (__cpuid): Remove definitions that handle %ebx
register in a special way.
(__cpuid_count): Ditto.
* config/i386/driver-i386.h: Protect with
"#if defined(__GNUC__) && (__GNUC__ >= 5 || !defined(__PIC__))".
(host_detect_local_cpu): Mention that GCC with non-fixed %ebx
is required to compile the function.
Bootstrapped and regression tested on x86_64-linux-gnu.
Uros.
Index: config/i386/cpuid.h
===================================================================
--- config/i386/cpuid.h (revision 216298)
+++ config/i386/cpuid.h (working copy)
@@ -146,56 +146,7 @@
#define signature_VORTEX_ecx 0x436f5320
#define signature_VORTEX_edx 0x36387865
-#if defined(__i386__) && defined(__PIC__)
-/* %ebx may be the PIC register. */
-#if __GNUC__ >= 3
#define __cpuid(level, a, b, c, d) \
- __asm__ ("xchg{l}\t{%%}ebx, %k1\n\t" \
- "cpuid\n\t" \
- "xchg{l}\t{%%}ebx, %k1\n\t" \
- : "=a" (a), "=&r" (b), "=c" (c), "=d" (d) \
- : "0" (level))
-
-#define __cpuid_count(level, count, a, b, c, d) \
- __asm__ ("xchg{l}\t{%%}ebx, %k1\n\t" \
- "cpuid\n\t" \
- "xchg{l}\t{%%}ebx, %k1\n\t" \
- : "=a" (a), "=&r" (b), "=c" (c), "=d" (d) \
- : "0" (level), "2" (count))
-#else
-/* Host GCCs older than 3.0 weren't supporting Intel asm syntax
- nor alternatives in i386 code. */
-#define __cpuid(level, a, b, c, d) \
- __asm__ ("xchgl\t%%ebx, %k1\n\t" \
- "cpuid\n\t" \
- "xchgl\t%%ebx, %k1\n\t" \
- : "=a" (a), "=&r" (b), "=c" (c), "=d" (d) \
- : "0" (level))
-
-#define __cpuid_count(level, count, a, b, c, d) \
- __asm__ ("xchgl\t%%ebx, %k1\n\t" \
- "cpuid\n\t" \
- "xchgl\t%%ebx, %k1\n\t" \
- : "=a" (a), "=&r" (b), "=c" (c), "=d" (d) \
- : "0" (level), "2" (count))
-#endif
-#elif defined(__x86_64__) && (defined(__code_model_medium__) ||
defined(__code_model_large__)) && defined(__PIC__)
-/* %rbx may be the PIC register. */
-#define __cpuid(level, a, b, c, d) \
- __asm__ ("xchg{q}\t{%%}rbx, %q1\n\t" \
- "cpuid\n\t" \
- "xchg{q}\t{%%}rbx, %q1\n\t" \
- : "=a" (a), "=&r" (b), "=c" (c), "=d" (d) \
- : "0" (level))
-
-#define __cpuid_count(level, count, a, b, c, d) \
- __asm__ ("xchg{q}\t{%%}rbx, %q1\n\t" \
- "cpuid\n\t" \
- "xchg{q}\t{%%}rbx, %q1\n\t" \
- : "=a" (a), "=&r" (b), "=c" (c), "=d" (d) \
- : "0" (level), "2" (count))
-#else
-#define __cpuid(level, a, b, c, d) \
__asm__ ("cpuid\n\t" \
: "=a" (a), "=b" (b), "=c" (c), "=d" (d) \
: "0" (level))
@@ -204,8 +155,8 @@
__asm__ ("cpuid\n\t" \
: "=a" (a), "=b" (b), "=c" (c), "=d" (d) \
: "0" (level), "2" (count))
-#endif
+
/* Return highest supported input value for cpuid instruction. ext can
be either 0x0 or 0x8000000 to return highest supported value for
basic or extended cpuid information. Function returns 0 if cpuid
Index: config/i386/driver-i386.c
===================================================================
--- config/i386/driver-i386.c (revision 216298)
+++ config/i386/driver-i386.c (working copy)
@@ -24,7 +24,7 @@
const char *host_detect_local_cpu (int argc, const char **argv);
-#ifdef __GNUC__
+#if defined(__GNUC__) && (__GNUC__ >= 5 || !defined(__PIC__))
#include "cpuid.h"
struct cache_desc
@@ -942,9 +942,9 @@
}
#else
-/* If we aren't compiling with GCC then the driver will just ignore
- -march and -mtune "native" target and will leave to the newly
- built compiler to generate code for its default target. */
+/* If we are compiling with GCC where %EBX register is fixed, then the
+ driver will just ignore -march and -mtune "native" target and will leave
+ to the newly built compiler to generate code for its default target. */
const char *host_detect_local_cpu (int, const char **)
{
