[PATCH V2] Setup predicate for switch default case in IPA (PR ipa/91089)

[Feng Xue OS <fxue at os dot amperecomputing dot com>]

> I have read through the patch and it looks OK to me but I cannot approve
> it, you have to ping Honza for that.  Since you decided to use the value
> range info, it would be nice if you could also add a testcase where it
> plays a role. 

It is somewhat hard to write a testcase to show role of range info only with
this patch. If another patch "Generalized predicate/condition for parameter
reference in IPA (PR ipa/91088)" is accepted, it will become easy and I will
update this testcase to show that.

And this new version also resolves a problem that we might generate very
complicated predicate for basic block in convergence point reached from
all switch cases.

       switch (index)
        /       |       \
case1   case2  ... default
        \       |       /
   convergence point

For switch/if statement, current algorithm synthesizes predicate of
convergence point by OR-combining predicates of all its cases/branches, which
might give us a very complicated one.  Actually, we can get simplified predicate
by using the fact that predicate for a basic block must also hold true for its post
dominators.  To be specific, convergence point should include (at least equal to)
predicate of the switch/if statement.

Honza & Martin,
    
  Would please review this new patch when you have time? Thanks.

Feng

-----
diff --git a/gcc/ipa-fnsummary.c b/gcc/ipa-fnsummary.c
index 278bf606661..dc5752fc005 100644
--- a/gcc/ipa-fnsummary.c
+++ b/gcc/ipa-fnsummary.c
@@ -1198,7 +1198,8 @@ set_cond_stmt_execution_predicate (struct ipa_func_body_info *fbi,
 	  /* invert_tree_comparison will return ERROR_MARK on FP
 	     comparsions that are not EQ/NE instead of returning proper
 	     unordered one.  Be sure it is not confused with NON_CONSTANT.  */
-	  if (this_code != ERROR_MARK)
+	  if (this_code != ERROR_MARK
+	      && !dominated_by_p (CDI_POST_DOMINATORS, bb, e->dest))
 	    {
 	      predicate p
 		= add_condition (summary, index, size, &aggpos, this_code,
@@ -1269,13 +1270,31 @@ set_switch_stmt_execution_predicate (struct ipa_func_body_info *fbi,
   if (!unmodified_parm_or_parm_agg_item (fbi, last, op, &index, &size, &aggpos))
     return;
 
+  auto_vec<std::pair<tree, tree> > ranges;
+  tree type = TREE_TYPE (op);
+  tree one_cst = build_one_cst (type);
+  int bound_limit = PARAM_VALUE (PARAM_IPA_MAX_SWITCH_PREDICATE_BOUNDS);
+  int bound_count = 0;
+  value_range_base vr;
+
+  get_range_info (op, vr);
+
   FOR_EACH_EDGE (e, ei, bb->succs)
     {
       e->aux = edge_predicate_pool.allocate ();
       *(predicate *) e->aux = false;
     }
+
+  e = gimple_switch_edge (cfun, last, 0);
+  /* Set BOUND_COUNT to maximum count to bypass computing predicate for
+     default case if its target basic block is in convergence point of all
+     switch cases, which can be determined by checking whether it
+     post-dominates the switch statement.  */
+  if (dominated_by_p (CDI_POST_DOMINATORS, bb, e->dest))
+    bound_count = INT_MAX;
+
   n = gimple_switch_num_labels (last);
-  for (case_idx = 0; case_idx < n; ++case_idx)
+  for (case_idx = 1; case_idx < n; ++case_idx)
     {
       tree cl = gimple_switch_label (last, case_idx);
       tree min, max;
@@ -1285,10 +1304,10 @@ set_switch_stmt_execution_predicate (struct ipa_func_body_info *fbi,
       min = CASE_LOW (cl);
       max = CASE_HIGH (cl);
 
-      /* For default we might want to construct predicate that none
-         of cases is met, but it is bit hard to do not having negations
-         of conditionals handy.  */
-      if (!min && !max)
+      /* The case's target basic block is in convergence point of all switch
+	 cases, its predicate should be at least as that of the switch
+	 statement.  */
+      if (dominated_by_p (CDI_POST_DOMINATORS, bb, e->dest))
 	p = true;
       else if (!max)
 	p = add_condition (summary, index, size, &aggpos, EQ_EXPR,
@@ -1304,7 +1323,111 @@ set_switch_stmt_execution_predicate (struct ipa_func_body_info *fbi,
 	}
       *(class predicate *) e->aux
 	= p.or_with (summary->conds, *(class predicate *) e->aux);
+
+      /* If there are too many disjoint case ranges, predicate for default
+	 case might become too complicated.  So add a limit here.  */
+      if (bound_count > bound_limit)
+	continue;
+
+      bool new_range = true;
+
+      if (!ranges.is_empty ())
+	{
+	  tree last_max_plus_one
+		= int_const_binop (PLUS_EXPR, ranges.last ().second, one_cst);
+
+	  /* Merge case ranges if they are continuous.  */
+	  if (tree_int_cst_equal (min, last_max_plus_one))
+	    new_range = false;
+	  else if (vr.kind () == VR_ANTI_RANGE)
+	    {
+	      tree min_minus_one = int_const_binop (MINUS_EXPR, min, one_cst);
+
+	      /* If two disjoint case ranges can be connected by anti-range
+		of switch index, combine them to one range.  */
+	      if (tree_int_cst_lt (vr.max (), min_minus_one))
+		vr.set_undefined ();
+	      else if (tree_int_cst_le (vr.min (), last_max_plus_one))
+		new_range = false;
+	    }
+	}
+
+      if (!max)
+	max = min;
+
+      /* Create/extend a case range.  And we count endpoints of range set,
+	 this number nearly equals to number of conditions that we will create
+	 for predicate of default case.  */
+      if (new_range)
+	{
+	  bound_count += (min == max) ? 1 : 2;
+	  ranges.safe_push (std::make_pair (min, max));
+	}
+      else
+	{
+	  bound_count += (ranges.last ().first == ranges.last ().second);
+	  ranges.last ().second = max;
+	}
+    }
+
+  e = gimple_switch_edge (cfun, last, 0);
+  if (bound_count > bound_limit)
+    {
+      *(class predicate *) e->aux = true;
+      return;
+    }
+
+  tree vr_min = vr.kind () == VR_RANGE ? vr.min () : TYPE_MIN_VALUE (type);
+  tree vr_max = vr.kind () == VR_RANGE ? vr.max () : TYPE_MAX_VALUE (type);
+  predicate p_seg = true;
+  predicate p_all = false;
+
+  /* Construct predicate to represent default range set that is negation of
+     all case ranges.  Case range is classified as containing single/non-single
+     values.  Suppose a piece of case ranges in the following.
+
+                [D1...D2]  [S1] ... [Sn]  [D3...D4]
+
+     To represent default case's range sets between two non-single value
+     case ranges (From D2 to D3), we construct predicate as:
+
+              D2 < x < D3 && x != S1 && ... && x != Sn
+   */
+  for (size_t i = 0; i < ranges.length (); i++)
+    {
+      tree min = ranges[i].first;
+      tree max = ranges[i].second;
+
+      if (min == max)
+	p_seg &= add_condition (summary, index, size, &aggpos, NE_EXPR,
+				unshare_expr_without_location (min));
+      else
+	{
+	  /* Do not create sub-predicate for range that is beyond low bound
+	     of switch index.  */
+	  if (tree_int_cst_lt (vr_min, min))
+	    {
+	      p_seg &= add_condition (summary, index, size, &aggpos, LT_EXPR,
+				      unshare_expr_without_location (min));
+	      p_all = p_all.or_with (summary->conds, p_seg);
+	    }
+
+	  /* Do not create sub-predicate for range that is beyond up bound
+	     of switch index.  */
+	  if (tree_int_cst_le (vr_max, max))
+	    {
+	      p_seg = false;
+	      break;
+	    }
+
+	  p_seg = add_condition (summary, index, size, &aggpos, GT_EXPR,
+				 unshare_expr_without_location (max));
+	}
     }
+
+  p_all = p_all.or_with (summary->conds, p_seg);
+  *(class predicate *) e->aux
+    = p_all.or_with (summary->conds, *(class predicate *) e->aux);
 }
 
 
@@ -1354,10 +1477,10 @@ compute_bb_predicates (struct ipa_func_body_info *fbi,
 		    break;
 		}
 	    }
-	  if (p == false)
-	    gcc_checking_assert (!bb->aux);
-	  else
+	  if (p != false)
 	    {
+	      basic_block pdom_bb;
+
 	      if (!bb->aux)
 		{
 		  done = false;
@@ -1376,6 +1499,34 @@ compute_bb_predicates (struct ipa_func_body_info *fbi,
 		      *((predicate *) bb->aux) = p;
 		    }
 		}
+
+	      /* For switch/if statement, we can OR-combine predicates of all
+		 its cases/branches to get predicate for basic block in their
+		 convergence point, but sometimes this will generate very
+		 complicated predicate.  Actually, we can get simplified
+		 predicate in another way by using the fact that predicate
+		 for a basic block must also hold true for its post dominators.
+		 To be specific, basic block in convergence point of
+		 conditional statement should include predicate of the
+		 statement.  */
+	      pdom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, bb);
+	      if (pdom_bb == EXIT_BLOCK_PTR_FOR_FN (my_function) || !pdom_bb)
+		;
+	      else if (!pdom_bb->aux)
+		{
+		  done = false;
+		  pdom_bb->aux = edge_predicate_pool.allocate ();
+		  *((predicate *) pdom_bb->aux) = p;
+		}
+	      else if (p != *(predicate *) pdom_bb->aux)
+		{
+		  p = p.or_with (summary->conds, *(predicate *)pdom_bb->aux);
+	          if (p != *(predicate *) pdom_bb->aux)
+		    {
+		      done = false;
+		      *((predicate *) pdom_bb->aux) = p;
+		    }
+		}
 	    }
 	}
     }
@@ -1980,6 +2131,7 @@ analyze_function_body (struct cgraph_node *node, bool early)
   if (opt_for_fn (node->decl, optimize))
     {
       calculate_dominance_info (CDI_DOMINATORS);
+      calculate_dominance_info (CDI_POST_DOMINATORS);
       if (!early)
         loop_optimizer_init (LOOPS_NORMAL | LOOPS_HAVE_RECORDED_EXITS);
       else
@@ -2360,6 +2512,7 @@ analyze_function_body (struct cgraph_node *node, bool early)
       else if (!ipa_edge_args_sum)
 	ipa_free_all_node_params ();
       free_dominance_info (CDI_DOMINATORS);
+      free_dominance_info (CDI_POST_DOMINATORS);
     }
   if (dump_file)
     {
diff --git a/gcc/params.def b/gcc/params.def
index 13001a7bb2d..1461aa4849d 100644
--- a/gcc/params.def
+++ b/gcc/params.def
@@ -1123,6 +1123,14 @@ DEFPARAM (PARAM_IPA_MAX_AA_STEPS,
 	  "parameter analysis based on alias analysis in any given function.",
 	  25000, 0, 0)
 
+DEFPARAM (PARAM_IPA_MAX_SWITCH_PREDICATE_BOUNDS,
+	  "ipa-max-switch-predicate-bounds",
+	  "Maximal number of boundary endpoints of case ranges of switch "
+	  "statement.  For switch exceeding this limit, do not construct cost-"
+	  "evaluating predicate for default case during IPA function summary"
+	  "generation.",
+	  5, 0, 0)
+
 /* WHOPR partitioning configuration.  */
 
 DEFPARAM (PARAM_LTO_PARTITIONS,
diff --git a/gcc/testsuite/gcc.dg/ipa/pr91089.c b/gcc/testsuite/gcc.dg/ipa/pr91089.c
new file mode 100644
index 00000000000..dbd9b8c94fe
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ipa/pr91089.c
@@ -0,0 +1,111 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fdump-ipa-cp-details -fdump-ipa-fnsummary-details --param ipa-max-switch-predicate-bounds=10 -fno-inline" } */
+
+int fn();
+
+int data;
+
+int callee1(int i)
+{
+  switch (i)
+    {
+      case -126:  return i + 13;
+      case -127:  return i + 5;
+      case -8:    return i * i;
+      case 0:     return i % 9;
+      case 5:
+      case 7:
+      case 6:     return 3;
+      default:
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+     }
+
+  return data += i;
+}
+
+int fn2();
+
+int callee2(int i)
+{
+  switch (i )
+    {
+      case 0:
+	fn();
+	fn();
+	fn();
+      case 1:
+	fn();
+	fn();
+      case -1:
+	fn();
+      case -2:
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	fn();
+	data += i;
+	break;
+    }
+
+  if (i == 1000)
+    {
+      int j;
+
+      for (j = 0; j < 100; j++)
+	fn2();
+    }
+  return i + 3;
+}		
+
+int caller()
+{
+  return callee1 (-127) +
+	 callee1 (-126) +
+	 callee1 (-8) +
+	 callee1 (0) +
+	 callee1 (5) +
+	 callee1 (6) +
+	 callee1 (7) +
+	 callee1 (100) +
+	 callee2 (9);
+	 callee2 (13);
+}
+ 
+/* { dg-final { scan-ipa-dump-times "Creating a specialized node of callee" 7 "cp" } } */
+/* { dg-final { scan-ipa-dump "op0 < -127" "fnsummary" } } */
+/* { dg-final { scan-ipa-dump "op0 > -126" "fnsummary" } } */
+/* { dg-final { scan-ipa-dump "op0 != -8"  "fnsummary" } } */
+/* { dg-final { scan-ipa-dump "op0 != 0"   "fnsummary" } } */
+/* { dg-final { scan-ipa-dump "op0 < 5"    "fnsummary" } } */
+/* { dg-final { scan-ipa-dump "op0 > 7"    "fnsummary" } } */
+/* { dg-final { scan-ipa-dump "loop depth: 1 .+ time:\[ \]*\[0-9\]+ predicate: \\(op0 == 1000\\)" "fnsummary" } } */
-- 
2.17.1