Clean up icc + ia64 situation.

Some googling turned up multiple sources saying that older versions of icc
do not accept gcc-compatible asm blocks on IA64, though asm does work on
x86[_64].  This is apparently fixed as of icc version 12.0 or so, but that
doesn't help us much; if we have to carry the extra implementation anyway,
we may as well just use it for icc rather than add a compiler version test.

Hence, revert commit 2c713d6ea2 (though I
separated the icc code from the gcc code completely, producing what seems
cleaner code).  Document the state of affairs more explicitly, both in
s_lock.h and postgres.c, and make some cosmetic adjustments around the
IA64 code in s_lock.h.

src/backend/tcop/postgres.c

@@ -2998,6 +2998,10 @@ ProcessInterrupts(void)
  * IA64-specific code to fetch the AR.BSP register for stack depth checks.
  *
  * We currently support gcc, icc, and HP-UX's native compiler here.
+ *
+ * Note: while icc accepts gcc asm blocks on x86[_64], this is not true on
+ * ia64 (at least not in icc versions before 12.x).  So we have to carry a
+ * separate implementation for it.
  */
 #if defined(__ia64__) || defined(__ia64)
 
@@ -3005,8 +3009,12 @@ ProcessInterrupts(void)
 /* Assume it's HP-UX native compiler */
 #include <ia64/sys/inline.h>
 #define ia64_get_bsp() ((char *) (_Asm_mov_from_ar(_AREG_BSP, _NO_FENCE)))
+#elif defined(__INTEL_COMPILER)
+/* icc */
+#include <asm/ia64regs.h>
+#define ia64_get_bsp() ((char *) __getReg(_IA64_REG_AR_BSP))
 #else
-/* Use inline assembly; works with gcc and icc */
+/* gcc */
 static __inline__ char *
 ia64_get_bsp(void)
 {

src/include/storage/s_lock.h

@@ -266,6 +266,10 @@ spin_delay(void)
  * any explicit statement on that in the gcc manual.  In Intel's compiler,
  * the -m[no-]serialize-volatile option controls that, and testing shows that
  * it is enabled by default.
+ *
+ * While icc accepts gcc asm blocks on x86[_64], this is not true on ia64
+ * (at least not in icc versions before 12.x).  So we have to carry a separate
+ * compiler-intrinsic-based implementation for it.
  */
 #define HAS_TEST_AND_SET
 
@@ -303,6 +307,10 @@ tas(volatile slock_t *lock)
 	return ret;
 }
 
+/* icc can't use the regular gcc S_UNLOCK() macro either in this case */
+#define S_UNLOCK(lock)	\
+	do { __memory_barrier(); *(lock) = 0; } while (0)
+
 #endif /* __INTEL_COMPILER */
 #endif	 /* __ia64__ || __ia64 */
 
@@ -671,22 +679,19 @@ typedef unsigned char slock_t;
 #endif
 
 /*
- * Note that this implementation is unsafe for any platform that can speculate
+ * Default implementation of S_UNLOCK() for gcc/icc.
+ *
+ * Note that this implementation is unsafe for any platform that can reorder
  * a memory access (either load or store) after a following store.  That
- * happens not to be possible x86 and most legacy architectures (some are
+ * happens not to be possible on x86 and most legacy architectures (some are
  * single-processor!), but many modern systems have weaker memory ordering.
- * Those that do must define their own version S_UNLOCK() rather than relying
- * on this one.
+ * Those that do must define their own version of S_UNLOCK() rather than
+ * relying on this one.
  */
 #if !defined(S_UNLOCK)
-#if defined(__INTEL_COMPILER)
-#define S_UNLOCK(lock)	\
-	do { __memory_barrier(); *(lock) = 0; } while (0)
-#else
 #define S_UNLOCK(lock)	\
 	do { __asm__ __volatile__("" : : : "memory");  *(lock) = 0; } while (0)
 #endif
-#endif
 
 #endif	/* defined(__GNUC__) || defined(__INTEL_COMPILER) */
 
@@ -793,7 +798,7 @@ tas(volatile slock_t *lock)
 
 #if defined(__hpux) && defined(__ia64) && !defined(__GNUC__)
 /*
- * HP-UX on Itanium, non-gcc compiler
+ * HP-UX on Itanium, non-gcc/icc compiler
  *
  * We assume that the compiler enforces strict ordering of loads/stores on
  * volatile data (see comments on the gcc-version earlier in this file).
@@ -816,7 +821,7 @@ typedef unsigned int slock_t;
 #define S_UNLOCK(lock)	\
 	do { _Asm_mf(); (*(lock)) = 0; } while (0)
 
-#endif	/* HPUX on IA64, non gcc */
+#endif	/* HPUX on IA64, non gcc/icc */
 
 #if defined(_AIX)	/* AIX */
 /*
@@ -935,7 +940,7 @@ extern int	tas_sema(volatile slock_t *lock);
 #if !defined(S_UNLOCK)
 /*
  * Our default implementation of S_UNLOCK is essentially *(lock) = 0.  This
- * is unsafe if the platform can speculate a memory access (either load or
+ * is unsafe if the platform can reorder a memory access (either load or
  * store) after a following store; platforms where this is possible must
  * define their own S_UNLOCK.  But CPU reordering is not the only concern:
  * if we simply defined S_UNLOCK() as an inline macro, the compiler might