changeset 51171:d9936e986e4f

8203915: Induction variable of over-unrolled loop conflicts with range checks Summary: Update skeleton predicates before main loop during unrolling to remove dead code. Reviewed-by: kvn, roland
author thartmann
date Thu, 14 Jun 2018 09:04:55 +0200
parents 83e2deb73612
children 27929b7eae4b
files src/hotspot/share/opto/loopPredicate.cpp src/hotspot/share/opto/loopTransform.cpp src/hotspot/share/opto/loopnode.hpp test/hotspot/jtreg/compiler/loopopts/IterationSplitPredicateInconsistency.java test/hotspot/jtreg/compiler/loopopts/TestOverunrolling.java
diffstat 5 files changed, 225 insertions(+), 118 deletions(-) [+]
line wrap: on
line diff
--- a/src/hotspot/share/opto/loopPredicate.cpp	Thu Jun 14 02:01:31 2018 -0400
+++ b/src/hotspot/share/opto/loopPredicate.cpp	Thu Jun 14 09:04:55 2018 +0200
@@ -89,7 +89,7 @@
 //
 //
 // We will create a region to guard the uct call if there is no one there.
-// The true projecttion (if_cont) of the new_iff is returned.
+// The true projection (if_cont) of the new_iff is returned.
 // This code is also used to clone predicates to cloned loops.
 ProjNode* PhaseIdealLoop::create_new_if_for_predicate(ProjNode* cont_proj, Node* new_entry,
                                                       Deoptimization::DeoptReason reason,
@@ -767,10 +767,10 @@
 }
 
 // After pre/main/post loops are created, we'll put a copy of some
-// range checks between the pre and main loop to validate the initial
-// value of the induction variable for the main loop. Make a copy of
-// the predicates here with an opaque node as a place holder for the
-// initial value.
+// range checks between the pre and main loop to validate the value
+// of the main loop induction variable. Make a copy of the predicates
+// here with an opaque node as a place holder for the value (will be
+// updated by PhaseIdealLoop::update_skeleton_predicate()).
 ProjNode* PhaseIdealLoop::insert_skeleton_predicate(IfNode* iff, IdealLoopTree *loop,
                                                     ProjNode* proj, ProjNode *predicate_proj,
                                                     ProjNode* upper_bound_proj,
--- a/src/hotspot/share/opto/loopTransform.cpp	Thu Jun 14 02:01:31 2018 -0400
+++ b/src/hotspot/share/opto/loopTransform.cpp	Thu Jun 14 09:04:55 2018 +0200
@@ -1014,125 +1014,143 @@
 // loop is never executed). When that happens, range check
 // CastII/ConvI2L nodes cause some data paths to die. For consistency,
 // the control paths must die too but the range checks were removed by
-// predication. The range checks that we add here guarantee that they
-// do.
+// predication. The range checks that we add here guarantee that they do.
 void PhaseIdealLoop::duplicate_predicates(CountedLoopNode* pre_head, Node* min_taken, Node* castii,
                                           IdealLoopTree* outer_loop, LoopNode* outer_main_head,
                                           uint dd_main_head) {
-  if (UseLoopPredicate) {
-    Node* entry = pre_head->in(LoopNode::EntryControl);
-    Node* predicate = NULL;
-    predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
-    if (predicate != NULL) {
+  assert(UseLoopPredicate, "loop predicates must be enabled");
+  Node* entry = pre_head->in(LoopNode::EntryControl);
+  Node* predicate = NULL;
+  predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
+  if (predicate != NULL) {
+    entry = entry->in(0)->in(0);
+  }
+  predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
+  if (predicate != NULL) {
+    IfNode* iff = entry->in(0)->as_If();
+    ProjNode* uncommon_proj = iff->proj_out(1 - entry->as_Proj()->_con);
+    Node* rgn = uncommon_proj->unique_ctrl_out();
+    assert(rgn->is_Region() || rgn->is_Call(), "must be a region or call uct");
+    assert(iff->in(1)->in(1)->Opcode() == Op_Opaque1, "unexpected predicate shape");
+    entry = entry->in(0)->in(0);
+    Node* prev_proj = min_taken;
+    while (entry != NULL && entry->is_Proj() && entry->in(0)->is_If()) {
+      iff = entry->in(0)->as_If();
+      uncommon_proj = iff->proj_out(1 - entry->as_Proj()->_con);
+      if (uncommon_proj->unique_ctrl_out() != rgn)
+        break;
+      if (iff->in(1)->Opcode() == Op_Opaque4) {
+        // Clone the predicate twice and initialize one with the initial
+        // value of the loop induction variable. Leave the other predicate
+        // to be initialized when increasing the stride during loop unrolling.
+        prev_proj = update_skeleton_predicate(iff, castii, entry, uncommon_proj, min_taken, outer_loop, prev_proj);
+        Node* value = new Opaque1Node(C, castii);
+        register_new_node(value, min_taken);
+        prev_proj = update_skeleton_predicate(iff, value, entry, uncommon_proj, min_taken, outer_loop, prev_proj);
+        // Remove the skeleton predicate from the pre-loop
+        _igvn.replace_input_of(iff, 1, _igvn.intcon(1));
+      }
       entry = entry->in(0)->in(0);
     }
-    predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
-    if (predicate != NULL) {
-      IfNode* iff = entry->in(0)->as_If();
-      ProjNode* uncommon_proj = iff->proj_out(1 - entry->as_Proj()->_con);
-      Node* rgn = uncommon_proj->unique_ctrl_out();
-      assert(rgn->is_Region() || rgn->is_Call(), "must be a region or call uct");
-      assert(iff->in(1)->in(1)->Opcode() == Op_Opaque1, "unexpected predicate shape");
-      entry = entry->in(0)->in(0);
-      Node* prev_proj = min_taken;
-      while (entry != NULL && entry->is_Proj() && entry->in(0)->is_If()) {
-        uncommon_proj = entry->in(0)->as_If()->proj_out(1 - entry->as_Proj()->_con);
-        if (uncommon_proj->unique_ctrl_out() != rgn)
-          break;
-        iff = entry->in(0)->as_If();
-        if (iff->in(1)->Opcode() == Op_Opaque4) {
-          Node_Stack to_clone(2);
-          to_clone.push(iff->in(1), 1);
-          uint current = C->unique();
-          Node* result = NULL;
-          // Look for the opaque node to replace with the init value
-          // and clone everything in between. We keep the Opaque4 node
-          // so the duplicated predicates are eliminated once loop
-          // opts are over: they are here only to keep the IR graph
-          // consistent.
-          do {
-            Node* n = to_clone.node();
-            uint i = to_clone.index();
-            Node* m = n->in(i);
-            int op = m->Opcode();
-            if (m->is_Bool() ||
-                m->is_Cmp() ||
-                op == Op_AndL ||
-                op == Op_OrL ||
-                op == Op_RShiftL ||
-                op == Op_LShiftL ||
-                op == Op_AddL ||
-                op == Op_AddI ||
-                op == Op_MulL ||
-                op == Op_MulI ||
-                op == Op_SubL ||
-                op == Op_SubI ||
-                op == Op_ConvI2L) {
-              to_clone.push(m, 1);
-              continue;
-            }
-            if (op == Op_Opaque1) {
-              if (n->_idx < current) {
-                n = n->clone();
-              }
-              n->set_req(i, castii);
-              register_new_node(n, min_taken);
-              to_clone.set_node(n);
-            }
-            for (;;) {
-              Node* cur = to_clone.node();
-              uint j = to_clone.index();
-              if (j+1 < cur->req()) {
-                to_clone.set_index(j+1);
-                break;
-              }
-              to_clone.pop();
-              if (to_clone.size() == 0) {
-                result = cur;
-                break;
-              }
-              Node* next = to_clone.node();
-              j = to_clone.index();
-              if (cur->_idx >= current) {
-                if (next->_idx < current) {
-                  next = next->clone();
-                  register_new_node(next, min_taken);
-                  to_clone.set_node(next);
-                }
-                assert(next->in(j) != cur, "input should have been cloned");
-                next->set_req(j, cur);
-              }
-            }
-          } while (result == NULL);
-          assert(result->_idx >= current, "new node expected");
-
-          Node* proj = entry->clone();
-          Node* other_proj = uncommon_proj->clone();
-          Node* new_iff = iff->clone();
-          new_iff->set_req(1, result);
-          proj->set_req(0, new_iff);
-          other_proj->set_req(0, new_iff);
-          Node *frame = new ParmNode(C->start(), TypeFunc::FramePtr);
-          register_new_node(frame, C->start());
-          // It's impossible for the predicate to fail at runtime. Use
-          // an Halt node.
-          Node* halt = new HaltNode(other_proj, frame);
-          C->root()->add_req(halt);
-          new_iff->set_req(0, prev_proj);
-
-          register_control(new_iff, outer_loop->_parent, prev_proj);
-          register_control(proj, outer_loop->_parent, new_iff);
-          register_control(other_proj, _ltree_root, new_iff);
-          register_control(halt, _ltree_root, other_proj);
-
-          prev_proj = proj;
+    _igvn.replace_input_of(outer_main_head, LoopNode::EntryControl, prev_proj);
+    set_idom(outer_main_head, prev_proj, dd_main_head);
+  }
+}
+
+Node* PhaseIdealLoop::update_skeleton_predicate(Node* iff, Node* value, Node* entry, Node* uncommon_proj,
+                                                Node* min_taken, IdealLoopTree* outer_loop, Node* prev_proj) {
+  bool clone = (outer_loop != NULL); // Clone the predicate?
+  Node_Stack to_clone(2);
+  to_clone.push(iff->in(1), 1);
+  uint current = C->unique();
+  Node* result = NULL;
+  // Look for the opaque node to replace with the new value
+  // and clone everything in between. We keep the Opaque4 node
+  // so the duplicated predicates are eliminated once loop
+  // opts are over: they are here only to keep the IR graph
+  // consistent.
+  do {
+    Node* n = to_clone.node();
+    uint i = to_clone.index();
+    Node* m = n->in(i);
+    int op = m->Opcode();
+    if (m->is_Bool() ||
+        m->is_Cmp() ||
+        op == Op_AndL ||
+        op == Op_OrL ||
+        op == Op_RShiftL ||
+        op == Op_LShiftL ||
+        op == Op_AddL ||
+        op == Op_AddI ||
+        op == Op_MulL ||
+        op == Op_MulI ||
+        op == Op_SubL ||
+        op == Op_SubI ||
+        op == Op_ConvI2L) {
+      to_clone.push(m, 1);
+      continue;
+    }
+    if (op == Op_Opaque1) {
+      if (!clone) {
+        // Update the input of the Opaque1Node and exit
+        _igvn.replace_input_of(m, 1, value);
+        return prev_proj;
+      }
+      if (n->_idx < current) {
+        n = n->clone();
+      }
+      n->set_req(i, value);
+      register_new_node(n, min_taken);
+      to_clone.set_node(n);
+    }
+    for (;;) {
+      Node* cur = to_clone.node();
+      uint j = to_clone.index();
+      if (j+1 < cur->req()) {
+        to_clone.set_index(j+1);
+        break;
+      }
+      to_clone.pop();
+      if (to_clone.size() == 0) {
+        result = cur;
+        break;
+      }
+      Node* next = to_clone.node();
+      j = to_clone.index();
+      if (clone && cur->_idx >= current) {
+        if (next->_idx < current) {
+          next = next->clone();
+          register_new_node(next, min_taken);
+          to_clone.set_node(next);
         }
-        entry = entry->in(0)->in(0);
+        assert(next->in(j) != cur, "input should have been cloned");
+        next->set_req(j, cur);
       }
-      _igvn.replace_input_of(outer_main_head, LoopNode::EntryControl, prev_proj);
-      set_idom(outer_main_head, prev_proj, dd_main_head);
     }
+  } while (result == NULL);
+  if (!clone) {
+    return NULL;
   }
+  assert(result->_idx >= current, "new node expected");
+
+  Node* proj = entry->clone();
+  Node* other_proj = uncommon_proj->clone();
+  Node* new_iff = iff->clone();
+  new_iff->set_req(1, result);
+  proj->set_req(0, new_iff);
+  other_proj->set_req(0, new_iff);
+  Node *frame = new ParmNode(C->start(), TypeFunc::FramePtr);
+  register_new_node(frame, C->start());
+  // It's impossible for the predicate to fail at runtime. Use an Halt node.
+  Node* halt = new HaltNode(other_proj, frame);
+  C->root()->add_req(halt);
+  new_iff->set_req(0, prev_proj);
+
+  register_control(new_iff, outer_loop->_parent, prev_proj);
+  register_control(proj, outer_loop->_parent, new_iff);
+  register_control(other_proj, _ltree_root, new_iff);
+  register_control(halt, _ltree_root, other_proj);
+  return proj;
 }
 
 //------------------------------insert_pre_post_loops--------------------------
@@ -1278,7 +1296,9 @@
   // CastII for the main loop:
   Node* castii = cast_incr_before_loop( pre_incr, min_taken, main_head );
   assert(castii != NULL, "no castII inserted");
-  duplicate_predicates(pre_head, min_taken, castii, outer_loop, outer_main_head, dd_main_head);
+  if (UseLoopPredicate) {
+    duplicate_predicates(pre_head, min_taken, castii, outer_loop, outer_main_head, dd_main_head);
+  }
 
   // Step B4: Shorten the pre-loop to run only 1 iteration (for now).
   // RCE and alignment may change this later.
@@ -1622,6 +1642,26 @@
   assert(old_trip_count > 1 &&
       (!adjust_min_trip || stride_p <= (1<<3)*loop_head->unrolled_count()), "sanity");
 
+  if (UseLoopPredicate) {
+    // Search for skeleton predicates and update them according to the new stride
+    Node* entry = ctrl;
+    while (entry != NULL && entry->is_Proj() && entry->in(0)->is_If()) {
+      IfNode* iff = entry->in(0)->as_If();
+      ProjNode* proj = iff->proj_out(1 - entry->as_Proj()->_con);
+      if (proj->unique_ctrl_out()->Opcode() != Op_Halt) {
+        break;
+      }
+      if (iff->in(1)->Opcode() == Op_Opaque4) {
+        // Compute value of loop induction variable at the end of the first iteration
+        Node* max_value = _igvn.intcon(2 * stride_con - (stride_con > 0 ? 1 : -1));
+        max_value = new AddINode(init, max_value);
+        register_new_node(max_value, get_ctrl(iff->in(1)));
+        update_skeleton_predicate(iff, max_value);
+      }
+      entry = entry->in(0)->in(0);
+    }
+  }
+
   // Adjust loop limit to keep valid iterations number after unroll.
   // Use (limit - stride) instead of (((limit - init)/stride) & (-2))*stride
   // which may overflow.
--- a/src/hotspot/share/opto/loopnode.hpp	Thu Jun 14 02:01:31 2018 -0400
+++ b/src/hotspot/share/opto/loopnode.hpp	Thu Jun 14 09:04:55 2018 +0200
@@ -735,6 +735,8 @@
   void duplicate_predicates(CountedLoopNode* pre_head, Node *min_taken, Node* castii,
                             IdealLoopTree* outer_loop, LoopNode* outer_main_head,
                             uint dd_main_head);
+  Node* update_skeleton_predicate(Node* iff, Node* value, Node* entry = NULL, Node* uncommon_proj = NULL,
+                                  Node* min_taken = NULL, IdealLoopTree* outer_loop = NULL, Node* prev_proj = NULL);
 
 public:
 
--- a/test/hotspot/jtreg/compiler/loopopts/IterationSplitPredicateInconsistency.java	Thu Jun 14 02:01:31 2018 -0400
+++ b/test/hotspot/jtreg/compiler/loopopts/IterationSplitPredicateInconsistency.java	Thu Jun 14 09:04:55 2018 +0200
@@ -23,11 +23,12 @@
 
 /**
  * @test
- * @bug 8193130
+ * @bug 8193130 8203915
  * @summary Bad graph when unrolled loop bounds conflicts with range checks
  *
  * @run main/othervm IterationSplitPredicateInconsistency
  * @run main/othervm -XX:-UseLoopPredicate IterationSplitPredicateInconsistency
+ * @run main/othervm -XX:LoopStripMiningIter=0 IterationSplitPredicateInconsistency
  *
  */
 
--- a/test/hotspot/jtreg/compiler/loopopts/TestOverunrolling.java	Thu Jun 14 02:01:31 2018 -0400
+++ b/test/hotspot/jtreg/compiler/loopopts/TestOverunrolling.java	Thu Jun 14 09:04:55 2018 +0200
@@ -23,11 +23,12 @@
 
 /*
  * @test
- * @bug 8159016 8202949
+ * @bug 8159016 8202949 8203915
  * @summary Tests correct dominator information after over-unrolling a loop.
  * @requires vm.gc == "Parallel" | vm.gc == "null"
  * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -XX:+UnlockExperimentalVMOptions
  *                   -Xcomp -XX:-TieredCompilation -XX:-UseSwitchProfiling
+ *                   -XX:-UseCountedLoopSafepoints -XX:LoopUnrollLimit=250
  *                   -XX:-UseG1GC -XX:+UseParallelGC compiler.loopopts.TestOverunrolling
  */
 
@@ -81,11 +82,74 @@
         }
     }
 
+    // Similar to test2 but we cannot statically determine the upper bound of
+    // the inner for loop and can therefore not prevent over-unrolling.
+    public static void test3(int[] array) {
+        int[] iArr = new int[8];
+        for (int i = 0; i < array.length; i++) {
+            for (int j = 5; j < i; j++) {
+                int k = 1;
+                do {
+                    iArr[j] = 0;
+                    switch (k) {
+                    case 1:
+                        lFld = 0;
+                        break;
+                    case 10:
+                        dFld = 0;
+                        break;
+                    }
+                } while (++k < 1);
+            }
+        }
+    }
+
+    // Similar to test3 but with negative stride and constant outer loop limit
+    public static void test4(int[] array, boolean store) {
+        int[] iArr = new int[8];
+        for (int i = -8; i < 8; i++) {
+            for (int j = 5; j > i; j--) {
+                int k = 1;
+                do {
+                    if (store) {
+                        iArr[j] = 0;
+                    }
+                    switch (k) {
+                    case 1:
+                        lFld = 0;
+                        break;
+                    case 10:
+                        dFld = 0;
+                        break;
+                    }
+                } while (++k < 1);
+            }
+        }
+    }
+
+    // The inner for-loop is over-unrolled and vectorized resulting in
+    // a crash in the matcher because the memory input to a vector is top.
+    public static int test5(int[] array) {
+        int result = 0;
+        int[] iArr = new int[8];
+        for (int i = 0; i < array.length; i++) {
+            for (int j = 5; j < i; j++) {
+                iArr[j] += array[j];
+                result += array[j];
+            }
+        }
+        return result;
+    }
+
     public static void main(String args[]) {
         for (int i = 0; i < 42; ++i) {
             test1(i);
         }
         test2();
+        int[] array = new int[8];
+        test3(array);
+        test4(array, false);
+        test5(array);
     }
 }