# HG changeset patch
# User eosterlund
# Date 1573122509 0
# Node ID 5d462d4b7a8bcc9f0db647398955a70d4e6a119f
# Parent  f79a8217d4c9eab38583641ad61a7205c65b8ac2
8233073: Make BitMap accessors more memory ordering friendly
Reviewed-by: kbarrett, pliden

diff -r f79a8217d4c9 -r 5d462d4b7a8b src/hotspot/share/c1/c1_Instruction.cpp
--- a/src/hotspot/share/c1/c1_Instruction.cpp	Tue Oct 22 11:55:58 2019 +0200
+++ b/src/hotspot/share/c1/c1_Instruction.cpp	Thu Nov 07 10:28:29 2019 +0000
@@ -29,6 +29,7 @@
 #include "c1/c1_ValueStack.hpp"
 #include "ci/ciObjArrayKlass.hpp"
 #include "ci/ciTypeArrayKlass.hpp"
+#include "utilities/bitMap.inline.hpp"
 
 
 // Implementation of Instruction
diff -r f79a8217d4c9 -r 5d462d4b7a8b src/hotspot/share/opto/graphKit.cpp
--- a/src/hotspot/share/opto/graphKit.cpp	Tue Oct 22 11:55:58 2019 +0200
+++ b/src/hotspot/share/opto/graphKit.cpp	Thu Nov 07 10:28:29 2019 +0000
@@ -43,6 +43,7 @@
 #include "opto/runtime.hpp"
 #include "runtime/deoptimization.hpp"
 #include "runtime/sharedRuntime.hpp"
+#include "utilities/bitMap.inline.hpp"
 
 //----------------------------GraphKit-----------------------------------------
 // Main utility constructor.
diff -r f79a8217d4c9 -r 5d462d4b7a8b src/hotspot/share/opto/parse1.cpp
--- a/src/hotspot/share/opto/parse1.cpp	Tue Oct 22 11:55:58 2019 +0200
+++ b/src/hotspot/share/opto/parse1.cpp	Thu Nov 07 10:28:29 2019 +0000
@@ -41,6 +41,7 @@
 #include "runtime/handles.inline.hpp"
 #include "runtime/safepointMechanism.hpp"
 #include "runtime/sharedRuntime.hpp"
+#include "utilities/bitMap.inline.hpp"
 #include "utilities/copy.hpp"
 
 // Static array so we can figure out which bytecodes stop us from compiling
diff -r f79a8217d4c9 -r 5d462d4b7a8b src/hotspot/share/utilities/bitMap.hpp
--- a/src/hotspot/share/utilities/bitMap.hpp	Tue Oct 22 11:55:58 2019 +0200
+++ b/src/hotspot/share/utilities/bitMap.hpp	Thu Nov 07 10:28:29 2019 +0000
@@ -26,6 +26,7 @@
 #define SHARE_UTILITIES_BITMAP_HPP
 
 #include "memory/allocation.hpp"
+#include "runtime/atomic.hpp"
 #include "utilities/align.hpp"
 
 // Forward decl;
@@ -105,6 +106,8 @@
   void set_word  (idx_t word)            { set_word(word, ~(bm_word_t)0); }
   void clear_word(idx_t word)            { _map[word] = 0; }
 
+  static inline const bm_word_t load_word_ordered(const volatile bm_word_t* const addr, atomic_memory_order memory_order);
+
   // Utilities for ranges of bits.  Ranges are half-open [beg, end).
 
   // Ranges within a single word.
@@ -204,6 +207,9 @@
     return (*word_addr(index) & bit_mask(index)) != 0;
   }
 
+  // memory_order must be memory_order_relaxed or memory_order_acquire.
+  bool par_at(idx_t index, atomic_memory_order memory_order = memory_order_acquire) const;
+
   // Align bit index up or down to the next bitmap word boundary, or check
   // alignment.
   static idx_t word_align_up(idx_t bit) {
@@ -220,9 +226,14 @@
   inline void set_bit(idx_t bit);
   inline void clear_bit(idx_t bit);
 
-  // Atomically set or clear the specified bit.
-  inline bool par_set_bit(idx_t bit);
-  inline bool par_clear_bit(idx_t bit);
+  // Attempts to change a bit to a desired value. The operation returns true if
+  // this thread changed the value of the bit. It was changed with a RMW operation
+  // using the specified memory_order. The operation returns false if the change
+  // could not be set due to the bit already being observed in the desired state.
+  // The atomic access that observed the bit in the desired state has acquire
+  // semantics, unless memory_order is memory_order_relaxed or memory_order_release.
+  inline bool par_set_bit(idx_t bit, atomic_memory_order memory_order = memory_order_conservative);
+  inline bool par_clear_bit(idx_t bit, atomic_memory_order memory_order = memory_order_conservative);
 
   // Put the given value at the given offset. The parallel version
   // will CAS the value into the bitmap and is quite a bit slower.
diff -r f79a8217d4c9 -r 5d462d4b7a8b src/hotspot/share/utilities/bitMap.inline.hpp
--- a/src/hotspot/share/utilities/bitMap.inline.hpp	Tue Oct 22 11:55:58 2019 +0200
+++ b/src/hotspot/share/utilities/bitMap.inline.hpp	Thu Nov 07 10:28:29 2019 +0000
@@ -26,6 +26,7 @@
 #define SHARE_UTILITIES_BITMAP_INLINE_HPP
 
 #include "runtime/atomic.hpp"
+#include "runtime/orderAccess.hpp"
 #include "utilities/bitMap.hpp"
 #include "utilities/count_trailing_zeros.hpp"
 
@@ -39,18 +40,39 @@
   *word_addr(bit) &= ~bit_mask(bit);
 }
 
-inline bool BitMap::par_set_bit(idx_t bit) {
+inline const BitMap::bm_word_t BitMap::load_word_ordered(const volatile bm_word_t* const addr, atomic_memory_order memory_order) {
+  if (memory_order == memory_order_relaxed || memory_order == memory_order_release) {
+    return Atomic::load(addr);
+  } else {
+    assert(memory_order == memory_order_acq_rel ||
+           memory_order == memory_order_acquire ||
+           memory_order == memory_order_conservative,
+           "unexpected memory ordering");
+    return OrderAccess::load_acquire(addr);
+  }
+}
+
+inline bool BitMap::par_at(idx_t index, atomic_memory_order memory_order) const {
+  verify_index(index);
+  assert(memory_order == memory_order_acquire ||
+         memory_order == memory_order_relaxed,
+         "unexpected memory ordering");
+  const volatile bm_word_t* const addr = word_addr(index);
+  return (load_word_ordered(addr, memory_order) & bit_mask(index)) != 0;
+}
+
+inline bool BitMap::par_set_bit(idx_t bit, atomic_memory_order memory_order) {
   verify_index(bit);
   volatile bm_word_t* const addr = word_addr(bit);
   const bm_word_t mask = bit_mask(bit);
-  bm_word_t old_val = *addr;
+  bm_word_t old_val = load_word_ordered(addr, memory_order);
 
   do {
     const bm_word_t new_val = old_val | mask;
     if (new_val == old_val) {
       return false;     // Someone else beat us to it.
     }
-    const bm_word_t cur_val = Atomic::cmpxchg(new_val, addr, old_val);
+    const bm_word_t cur_val = Atomic::cmpxchg(new_val, addr, old_val, memory_order);
     if (cur_val == old_val) {
       return true;      // Success.
     }
@@ -58,18 +80,18 @@
   } while (true);
 }
 
-inline bool BitMap::par_clear_bit(idx_t bit) {
+inline bool BitMap::par_clear_bit(idx_t bit, atomic_memory_order memory_order) {
   verify_index(bit);
   volatile bm_word_t* const addr = word_addr(bit);
   const bm_word_t mask = ~bit_mask(bit);
-  bm_word_t old_val = *addr;
+  bm_word_t old_val = load_word_ordered(addr, memory_order);
 
   do {
     const bm_word_t new_val = old_val & mask;
     if (new_val == old_val) {
       return false;     // Someone else beat us to it.
     }
-    const bm_word_t cur_val = Atomic::cmpxchg(new_val, addr, old_val);
+    const bm_word_t cur_val = Atomic::cmpxchg(new_val, addr, old_val, memory_order);
     if (cur_val == old_val) {
       return true;      // Success.
     }