Backport <b2ccc9731e3a183bc6f31480c7d12f110633ea2b>

src/hotspot/share/opto/chaitin.cpp

@@ -220,41 +220,60 @@ PhaseChaitin::PhaseChaitin(uint unique, PhaseCFG &cfg, Matcher &matcher, bool sc
   _high_frequency_lrg = MIN2(double(OPTO_LRG_HIGH_FREQ), _cfg.get_outer_loop_frequency());
 
   // Build a list of basic blocks, sorted by frequency
-  _blks = NEW_RESOURCE_ARRAY(Block *, _cfg.number_of_blocks());
   // Experiment with sorting strategies to speed compilation
+  uint nr_blocks = _cfg.number_of_blocks();
   double  cutoff = BLOCK_FREQUENCY(1.0); // Cutoff for high frequency bucket
   Block **buckets[NUMBUCKS];             // Array of buckets
   uint    buckcnt[NUMBUCKS];             // Array of bucket counters
   double  buckval[NUMBUCKS];             // Array of bucket value cutoffs
+
+  // The space which our buckets point into.
+  Block** start = NEW_RESOURCE_ARRAY(Block *, nr_blocks*NUMBUCKS);
+
   for (uint i = 0; i < NUMBUCKS; i++) {
-    buckets[i] = NEW_RESOURCE_ARRAY(Block *, _cfg.number_of_blocks());
+    buckets[i] = &start[i*nr_blocks];
     buckcnt[i] = 0;
     // Bump by three orders of magnitude each time
     cutoff *= 0.001;
     buckval[i] = cutoff;
-    for (uint j = 0; j < _cfg.number_of_blocks(); j++) {
-      buckets[i][j] = nullptr;
-    }
   }
+
   // Sort blocks into buckets
-  for (uint i = 0; i < _cfg.number_of_blocks(); i++) {
+  for (uint i = 0; i < nr_blocks; i++) {
     for (uint j = 0; j < NUMBUCKS; j++) {
-      if ((j == NUMBUCKS - 1) || (_cfg.get_block(i)->_freq > buckval[j])) {
+      double bval = buckval[j];
+      Block* blk = _cfg.get_block(i);
+      if (j == NUMBUCKS - 1 || blk->_freq > bval) {
+        uint cnt = buckcnt[j];
         // Assign block to end of list for appropriate bucket
-        buckets[j][buckcnt[j]++] = _cfg.get_block(i);
+        buckets[j][cnt] = blk;
+        buckcnt[j] = cnt+1;
         break; // kick out of inner loop
       }
     }
   }
-  // Dump buckets into final block array
+
+  // Squash the partially filled buckets together into the first one.
+  static_assert(NUMBUCKS >= 2, "must"); // If this isn't true then it'll mess up the squashing.
+  Block** offset = &buckets[0][buckcnt[0]];
+  for (int i = 1; i < NUMBUCKS; i++) {
+    ::memmove(offset, buckets[i], buckcnt[i]*sizeof(Block*));
+    offset += buckcnt[i];
+  }
+  assert((&buckets[0][0] + nr_blocks) == offset, "should be");
+
+  // Free the now unused memory
+  FREE_RESOURCE_ARRAY(Block*, buckets[1], (NUMBUCKS-1)*nr_blocks);
+  // Finally, point the _blks to our memory
+  _blks = buckets[0];
+
+#ifdef ASSERT
   uint blkcnt = 0;
   for (uint i = 0; i < NUMBUCKS; i++) {
-    for (uint j = 0; j < buckcnt[i]; j++) {
-      _blks[blkcnt++] = buckets[i][j];
-    }
+    blkcnt += buckcnt[i];
   }
-
-  assert(blkcnt == _cfg.number_of_blocks(), "Block array not totally filled");
+  assert(blkcnt == nr_blocks, "Block array not totally filled");
+#endif
 }
 
 // union 2 sets together.