Fix atomic operations on PA-RISC 2.0 processors.

PA-RISC 2.0 supports out-of-order execution for loads and stores.
Thus, we need to synchonize memory accesses.

This change revises the lock releases in __exchange_and_add and
__atomic_add to use an ordered store with release semantics.  We
also use an ordered load in the inner spin loop.

We use the "ldcw,co" instruction instead of "ldcw" when compiled
for PA 2.0.  Most PA 2.0 processors are coherent and can execute
the ldcw instruction in cache for improved performance.

Finally, the inner spin loop is revised to immediately branch to
the ldcw instruction when it detects the lock is free.

2023-01-05  John David Anglin  <danglin@gcc.gnu.org>

libstdc++-v3/ChangeLog:

	* config/cpu/hppa/atomicity.h (_PA_LDCW_INSN): Define.
	(__exchange_and_add): Use _PA_LDCW_INSN.  Use ordered store for
	lock release.  Revise loop.
	(__atomic_add): Likewise.

diff --git a/libstdc++-v3/config/cpu/hppa/atomicity.h b/libstdc++-v3/config/cpu/hppa/atomicity.h
index bb997e70c1d47dc1c7bb23163c8318e257aff924..658073537a44b55f0d8538e57a716bd731837b54 100644 (file)
--- a/libstdc++-v3/config/cpu/hppa/atomicity.h
+++ b/libstdc++-v3/config/cpu/hppa/atomicity.h
@@ -25,6 +25,15 @@
 #include <bits/c++config.h>
 #include <ext/atomicity.h>
 
+/* Perform ldcw operation in cache when possible.  */
+#ifndef _PA_LDCW_INSN
+# ifdef _PA_RISC2_0
+# define _PA_LDCW_INSN "ldcw,co"
+# else
+# define _PA_LDCW_INSN "ldcw"
+# endif
+#endif
+
 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
@@ -51,19 +60,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     int tmp;
     volatile int& lock = _Atomicity_lock<0>::_S_atomicity_lock;
 
-    __asm__ __volatile__ ("ldcw 0(%1),%0\n\t"
+    __asm__ __volatile__ (_PA_LDCW_INSN " 0(%1),%0\n\t"
                          "cmpib,<>,n 0,%0,.+20\n\t"
-                         "ldw 0(%1),%0\n\t"
-                         "cmpib,= 0,%0,.-4\n\t"
+                         "ldw,ma 0(%1),%0\n\t"
+                         "cmpib,<> 0,%0,.-12\n\t"
                          "nop\n\t"
-                         "b,n .-20"
+                         "b,n .-12"
                          : "=&r" (tmp)
                          : "r" (&lock)
                          : "memory");
 
     result = *__mem;
     *__mem = result + __val;
-    __asm__ __volatile__ ("stw %1,0(%0)"
+    __asm__ __volatile__ ("stw,ma %1,0(%0)"
                          : : "r" (&lock), "r" (tmp) : "memory");
     return result;
   }
@@ -75,18 +84,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     int tmp;
     volatile int& lock = _Atomicity_lock<0>::_S_atomicity_lock;
 
-    __asm__ __volatile__ ("ldcw 0(%1),%0\n\t"
+    __asm__ __volatile__ (_PA_LDCW_INSN " 0(%1),%0\n\t"
                          "cmpib,<>,n 0,%0,.+20\n\t"
-                         "ldw 0(%1),%0\n\t"
-                         "cmpib,= 0,%0,.-4\n\t"
+                         "ldw,ma 0(%1),%0\n\t"
+                         "cmpib,<> 0,%0,.-12\n\t"
                          "nop\n\t"
-                         "b,n .-20"
+                         "b,n .-12"
                          : "=&r" (tmp)
                          : "r" (&lock)
                          : "memory");
 
     *__mem += __val;
-    __asm__ __volatile__ ("stw %1,0(%0)"
+    __asm__ __volatile__ ("stw,ma %1,0(%0)"
                          : : "r" (&lock), "r" (tmp) : "memory");
   }