[gcc r13-5036] Fix atomic operations on PA-RISC 2.0 processors.

[John David Anglin <danglin@gcc.gnu.org>]

https://gcc.gnu.org/g:9807c31af91326988d083436483f9577296e1f9a

commit r13-5036-g9807c31af91326988d083436483f9577296e1f9a
Author: John David Anglin <danglin@gcc.gnu.org>
Date:   Thu Jan 5 18:15:18 2023 +0000

    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:
---
 libstdc++-v3/config/cpu/hppa/atomicity.h | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/libstdc++-v3/config/cpu/hppa/atomicity.h b/libstdc++-v3/config/cpu/hppa/atomicity.h
index bb997e70c1d..658073537a4 100644
--- 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");
   }