[gcc(refs/users/marxin/heads/loop-unswitching-switch-v5)] Loop unswitching: support gswitch statements.

[Martin Liska <marxin@gcc.gnu.org>]

https://gcc.gnu.org/g:cf96b955f5a9a5e1ad7fcbeec892257ce3c8ebea

commit cf96b955f5a9a5e1ad7fcbeec892257ce3c8ebea
Author: Martin Liska <mliska@suse.cz>
Date:   Wed Sep 1 13:04:15 2021 +0200

    Loop unswitching: support gswitch statements.
    
    The patch extends the loop unswitching pass so that gswitch
    statements are supported. The pass now uses ranger which marks
    switch edges that are known to be unreachable in a versioned loop.
    
    gcc/ChangeLog:
    
            * tree-cfg.c (gimple_lv_add_condition_to_bb): Support non-gimple
            expressions that needs to be gimplified.
            * tree-ssa-loop-unswitch.c (tree_unswitch_loop): Add new
            cond_edge argument.
            (tree_may_unswitch_on): Support gswitch statements.
            (clean_up_switches): New function.
            (tree_ssa_unswitch_loops): Call clean_up_switches.
            (tree_unswitch_single_loop): Change assumptions.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.dg/loop-unswitch-6.c: New test.
            * gcc.dg/loop-unswitch-7.c: New test.
            * gcc.dg/loop-unswitch-8.c: New test.
            * gcc.dg/loop-unswitch-9.c: New test.
            * gcc.dg/loop-unswitch-10.c: New test.
            * gcc.dg/loop-unswitch-11.c: New test.
    
    Co-Authored-By: Richard Biener <rguenther@suse.de>

Diff:
---
 gcc/testsuite/gcc.dg/loop-unswitch-10.c |  28 ++++
 gcc/testsuite/gcc.dg/loop-unswitch-11.c |  60 ++++++++
 gcc/testsuite/gcc.dg/loop-unswitch-6.c  |  56 +++++++
 gcc/testsuite/gcc.dg/loop-unswitch-7.c  |  45 ++++++
 gcc/testsuite/gcc.dg/loop-unswitch-8.c  |  28 ++++
 gcc/testsuite/gcc.dg/loop-unswitch-9.c  |  34 +++++
 gcc/tree-cfg.c                          |   7 +-
 gcc/tree-ssa-loop-unswitch.c            | 256 ++++++++++++++++++++++++++------
 8 files changed, 468 insertions(+), 46 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/loop-unswitch-10.c b/gcc/testsuite/gcc.dg/loop-unswitch-10.c
new file mode 100644
index 00000000000..747de272935
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/loop-unswitch-10.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -funswitch-loops -fdump-tree-unswitch-details" } */
+
+int
+foo(double *a, double *b, double *c, double *d, double *r, int size, float order)
+{
+  for (int i = 0; i < size; i++)
+  {
+    double tmp;
+
+    if (order == 1.f)
+      tmp = -8 * a[i];
+    else
+      tmp = -4 * b[i];
+
+    double x = 3 * tmp + d[i] + tmp;
+
+    if (order == 1.f)
+      x += 2;
+
+    double y = 3.4f * tmp + d[i];
+    r[i] = x + y;
+  }
+
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order.* == 1.0e" 1 "unswitch" } } */
diff --git a/gcc/testsuite/gcc.dg/loop-unswitch-11.c b/gcc/testsuite/gcc.dg/loop-unswitch-11.c
new file mode 100644
index 00000000000..30f4f347f7b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/loop-unswitch-11.c
@@ -0,0 +1,60 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -funswitch-loops -fdump-tree-unswitch-details --param=max-unswitch-insns=1000 --param=max-unswitch-level=10" } */
+
+int
+__attribute__((noipa))
+foo(double *a, double *b, double *c, double *d, double *r, int size, int order)
+{
+  for (int i = 0; i < size; i++)
+  {
+    double tmp, tmp2;
+
+    if (order <= 0)
+      tmp = 123;
+
+    switch(order)
+    {
+      case 0:
+        tmp += -8 * a[i];
+        tmp2 = 2 * b[i];
+        break;
+      case 1: 
+        tmp = 3 * a[i] -  2 * b[i];
+        tmp2 = 5 * b[i] - 2 * c[i];
+        break;
+      case 2:
+        tmp = 9 * a[i] +  2 * b[i] + c[i];
+        tmp2 = 4 * b[i] + 2 * c[i] + 8 * d[i];
+        break;
+      case 3:
+        tmp = 3 * a[i] +  2 * b[i] - c[i];
+        tmp2 = b[i] - 2 * c[i] + 8 * d[i];
+        break;
+      defaut:
+        __builtin_unreachable ();
+    }
+
+    double x = 3 * tmp + d[i] + tmp;
+    double y = 3.4f * tmp + d[i] + tmp2;
+    r[i] = x + y;
+  }
+
+  return 0;
+}
+
+#define N 16 * 1024
+double aa[N], bb[N], cc[N], dd[N], rr[N];
+
+int main()
+{
+  for (int i = 0; i < 100 * 1000; i++)
+    foo (aa, bb, cc, dd, rr, N, i % 4);
+}
+
+
+/* Test that we actually unswitched something.  */
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order.* <= 0" 1 "unswitch" } } */
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order.* == 0" 1 "unswitch" } } */
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order.* == 1" 1 "unswitch" } } */
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order.* == 2" 1 "unswitch" } } */
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order.* == 3" 1 "unswitch" } } */
diff --git a/gcc/testsuite/gcc.dg/loop-unswitch-6.c b/gcc/testsuite/gcc.dg/loop-unswitch-6.c
new file mode 100644
index 00000000000..315d6850877
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/loop-unswitch-6.c
@@ -0,0 +1,56 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -funswitch-loops -fdump-tree-unswitch-details --param=max-unswitch-insns=1000 --param=max-unswitch-level=10" } */
+
+int
+__attribute__((noipa))
+foo(double *a, double *b, double *c, double *d, double *r, int size, int order)
+{
+  for (int i = 0; i < size; i++)
+  {
+    double tmp, tmp2;
+
+    switch(order)
+    {
+      case 0:
+        tmp = -8 * a[i];
+        tmp2 = 2 * b[i];
+        break;
+      case 1: 
+        tmp = 3 * a[i] -  2 * b[i];
+        tmp2 = 5 * b[i] - 2 * c[i];
+        break;
+      case 2:
+        tmp = 9 * a[i] +  2 * b[i] + c[i];
+        tmp2 = 4 * b[i] + 2 * c[i] + 8 * d[i];
+        break;
+      case 3:
+        tmp = 3 * a[i] +  2 * b[i] - c[i];
+        tmp2 = b[i] - 2 * c[i] + 8 * d[i];
+        break;
+      defaut:
+        __builtin_unreachable ();
+    }
+
+    double x = 3 * tmp + d[i] + tmp;
+    double y = 3.4f * tmp + d[i] + tmp2;
+    r[i] = x + y;
+  }
+
+  return 0;
+}
+
+#define N 16 * 1024
+double aa[N], bb[N], cc[N], dd[N], rr[N];
+
+int main()
+{
+  for (int i = 0; i < 100 * 1000; i++)
+    foo (aa, bb, cc, dd, rr, N, i % 4);
+}
+
+
+/* Test that we actually unswitched something.  */
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order.* == 0" 1 "unswitch" } } */
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order.* == 1" 1 "unswitch" } } */
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order.* == 2" 1 "unswitch" } } */
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order.* == 3" 1 "unswitch" } } */
diff --git a/gcc/testsuite/gcc.dg/loop-unswitch-7.c b/gcc/testsuite/gcc.dg/loop-unswitch-7.c
new file mode 100644
index 00000000000..efabd52886c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/loop-unswitch-7.c
@@ -0,0 +1,45 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -funswitch-loops -fdump-tree-unswitch-details --param=max-unswitch-insns=1000 --param=max-unswitch-level=10" } */
+
+int
+foo(double *a, double *b, double *c, double *d, double *r, int size, int order)
+{
+  for (int i = 0; i < size; i++)
+  {
+    double tmp, tmp2;
+
+    switch(order)
+    {
+      case 5 ... 6:
+      case 9:
+        tmp = -8 * a[i];
+        tmp2 = 2 * b[i];
+        break;
+      case 11: 
+        tmp = 3 * a[i] -  2 * b[i];
+        tmp2 = 5 * b[i] - 2 * c[i];
+        break;
+      case 22:
+        tmp = 9 * a[i] +  2 * b[i] + c[i];
+        tmp2 = 4 * b[i] + 2 * c[i] + 8 * d[i];
+        break;
+      case 33:
+        tmp = 3 * a[i] +  2 * b[i] - c[i];
+        tmp2 = b[i] - 2 * c[i] + 8 * d[i];
+        break;
+      defaut:
+        __builtin_unreachable ();
+    }
+
+    double x = 3 * tmp + d[i] + tmp;
+    double y = 3.4f * tmp + d[i] + tmp2;
+    r[i] = x + y;
+  }
+
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order_.* >= 5 & order_.* <= 6 \\| order_.* == 9" 1 "unswitch" } } */
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order.* == 1" 1 "unswitch" } } */
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order.* == 2" 1 "unswitch" } } */
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order.* == 3" 1 "unswitch" } } */
diff --git a/gcc/testsuite/gcc.dg/loop-unswitch-8.c b/gcc/testsuite/gcc.dg/loop-unswitch-8.c
new file mode 100644
index 00000000000..4cec1f53bcc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/loop-unswitch-8.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -funswitch-loops -fdump-tree-unswitch-details" } */
+
+int
+foo(double *a, double *b, double *c, double *d, double *r, int size, int order)
+{
+  for (int i = 0; i < size; i++)
+  {
+    double tmp;
+
+    if (order == 1)
+      tmp = -8 * a[i];
+    else
+      tmp = -4 * b[i];
+
+    double x = 3 * tmp + d[i] + tmp;
+
+    if (order == 1)
+      x += 2;
+
+    double y = 3.4f * tmp + d[i];
+    r[i] = x + y;
+  }
+
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order.* == 1" 1 "unswitch" } } */
diff --git a/gcc/testsuite/gcc.dg/loop-unswitch-9.c b/gcc/testsuite/gcc.dg/loop-unswitch-9.c
new file mode 100644
index 00000000000..3058d4a5b38
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/loop-unswitch-9.c
@@ -0,0 +1,34 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -funswitch-loops -fdump-tree-unswitch-details" } */
+
+int
+foo(double *a, double *b, double *c, double *d, double *r, int size, unsigned order)
+{
+  for (int i = 0; i < size; i++)
+  {
+    double tmp;
+
+    switch (order)
+      {
+      case 0 ... 4:
+	tmp = -8 * a[i];
+	break;
+      default:
+	tmp = -4 * b[i];
+	break;
+      }
+
+    double x = 3 * tmp + d[i] + tmp;
+
+    /* This should not be unswitched as it's mutually excluded with case 0 ... 4.  */
+    if (order >= 5)
+      x += 2;
+
+    double y = 3.4f * tmp + d[i];
+    r[i] = x + y;
+  }
+
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-times ";; Unswitching loop with condition: order.* <= 4" 1 "unswitch" } } */
diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
index 8ed8c69b5b1..7db54f1cda2 100644
--- a/gcc/tree-cfg.c
+++ b/gcc/tree-cfg.c
@@ -9062,11 +9062,16 @@ gimple_lv_add_condition_to_bb (basic_block first_head ATTRIBUTE_UNUSED,
   edge e0;
 
   /* Build new conditional expr */
+  gsi = gsi_last_bb (cond_bb);
+
+  cond_expr = force_gimple_operand_gsi_1 (&gsi, cond_expr,
+					  is_gimple_condexpr_for_cond,
+					  NULL_TREE, false,
+					  GSI_CONTINUE_LINKING);
   new_cond_expr = gimple_build_cond_from_tree (cond_expr,
 					       NULL_TREE, NULL_TREE);
 
   /* Add new cond in cond_bb.  */
-  gsi = gsi_last_bb (cond_bb);
   gsi_insert_after (&gsi, new_cond_expr, GSI_NEW_STMT);
 
   /* Adjust edges appropriately to connect new head with first head
diff --git a/gcc/tree-ssa-loop-unswitch.c b/gcc/tree-ssa-loop-unswitch.c
index fe4dacc0833..45d53f5a6da 100644
--- a/gcc/tree-ssa-loop-unswitch.c
+++ b/gcc/tree-ssa-loop-unswitch.c
@@ -37,6 +37,10 @@ along with GCC; see the file COPYING3.  If not see
 #include "gimple-iterator.h"
 #include "cfghooks.h"
 #include "tree-ssa-loop-manip.h"
+#include "cfganal.h"
+#include "tree-cfgcleanup.h"
+#include "tree-pretty-print.h"
+#include "gimple-range.h"
 
 /* This file implements the loop unswitching, i.e. transformation of loops like
 
@@ -74,9 +78,9 @@ along with GCC; see the file COPYING3.  If not see
    tree-ssa-loop-im.c ensures that all the suitable conditions are in this
    shape.  */
 
-static class loop *tree_unswitch_loop (class loop *, basic_block, tree);
+static class loop *tree_unswitch_loop (class loop *, basic_block, tree, edge);
 static bool tree_unswitch_single_loop (class loop *, int);
-static tree tree_may_unswitch_on (basic_block, class loop *);
+static tree tree_may_unswitch_on (basic_block, class loop *, edge *);
 static bool tree_unswitch_outer_loop (class loop *);
 static edge find_loop_guard (class loop *);
 static bool empty_bb_without_guard_p (class loop *, basic_block);
@@ -84,6 +88,7 @@ static bool used_outside_loop_p (class loop *, tree);
 static void hoist_guard (class loop *, edge);
 static bool check_exit_phi (class loop *);
 static tree get_vop_from_header (class loop *);
+static void clean_up_switches (void);
 
 /* Main entry point.  Perform loop unswitching on all suitable loops.  */
 
@@ -103,7 +108,10 @@ tree_ssa_unswitch_loops (void)
     }
 
   if (changed)
-    return TODO_cleanup_cfg;
+    {
+      clean_up_switches ();
+      return TODO_cleanup_cfg;
+    }
   return 0;
 }
 
@@ -182,47 +190,114 @@ is_maybe_undefined (const tree name, gimple *stmt, class loop *loop)
 }
 
 /* Checks whether we can unswitch LOOP on condition at end of BB -- one of its
-   basic blocks (for what it means see comments below).  */
+   basic blocks (for what it means see comments below).
+   When a gswitch case is returned, fill up COND_EDGE for it.  */
 
 static tree
-tree_may_unswitch_on (basic_block bb, class loop *loop)
+tree_may_unswitch_on (basic_block bb, class loop *loop, edge *cond_edge)
 {
   gimple *last, *def;
-  gcond *stmt;
-  tree cond, use;
+  tree use;
   basic_block def_bb;
   ssa_op_iter iter;
 
   /* BB must end in a simple conditional jump.  */
   last = last_stmt (bb);
-  if (!last || gimple_code (last) != GIMPLE_COND)
-    return NULL_TREE;
-  stmt = as_a <gcond *> (last);
+  if (gcond *stmt = safe_dyn_cast <gcond *> (last))
+    {
+      /* To keep the things simple, we do not directly remove the conditions,
+	 but just replace tests with 0 != 0 resp. 1 != 0.  Prevent the infinite
+	 loop where we would unswitch again on such a condition.  */
+      if (gimple_cond_true_p (stmt) || gimple_cond_false_p (stmt))
+	return NULL_TREE;
 
-  /* To keep the things simple, we do not directly remove the conditions,
-     but just replace tests with 0 != 0 resp. 1 != 0.  Prevent the infinite
-     loop where we would unswitch again on such a condition.  */
-  if (gimple_cond_true_p (stmt) || gimple_cond_false_p (stmt))
-    return NULL_TREE;
+      /* Condition must be invariant.  */
+      FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
+	{
+	  def = SSA_NAME_DEF_STMT (use);
+	  def_bb = gimple_bb (def);
+	  if (def_bb
+	      && flow_bb_inside_loop_p (loop, def_bb))
+	    return NULL_TREE;
+	  /* Unswitching on undefined values would introduce undefined
+	     behavior that the original program might never exercise.  */
+	  if (is_maybe_undefined (use, stmt, loop))
+	    return NULL_TREE;
+	}
 
-  /* Condition must be invariant.  */
-  FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
+      edge e1 = EDGE_SUCC (bb, 0);
+      edge e2 = EDGE_SUCC (bb, 1);
+      *cond_edge = e1->flags & EDGE_TRUE_VALUE ? e1 : e2;
+      return build2 (gimple_cond_code (stmt), boolean_type_node,
+		     gimple_cond_lhs (stmt), gimple_cond_rhs (stmt));
+    }
+  else if (gswitch *stmt = safe_dyn_cast <gswitch *> (last))
     {
-      def = SSA_NAME_DEF_STMT (use);
+      unsigned nlabels = gimple_switch_num_labels (stmt);
+      tree idx = gimple_switch_index (stmt);
+      if (TREE_CODE (idx) != SSA_NAME
+	  || nlabels < 1)
+	return NULL_TREE;
+      /* Index must be invariant.  */
+      def = SSA_NAME_DEF_STMT (idx);
       def_bb = gimple_bb (def);
       if (def_bb
 	  && flow_bb_inside_loop_p (loop, def_bb))
 	return NULL_TREE;
       /* Unswitching on undefined values would introduce undefined
 	 behavior that the original program might never exercise.  */
-      if (is_maybe_undefined (use, stmt, loop))
+      if (is_maybe_undefined (idx, stmt, loop))
 	return NULL_TREE;
-    }
 
-  cond = build2 (gimple_cond_code (stmt), boolean_type_node,
-		 gimple_cond_lhs (stmt), gimple_cond_rhs (stmt));
+      edge e;
+      edge_iterator ei;
+      FOR_EACH_EDGE (e, ei, gimple_bb (stmt)->succs)
+	{
+	  if (!(e->flags & EDGE_IGNORE))
+	    {
+	      /* Build compound expression for all cases leading
+		 to this edge.  */
+	      tree expr = NULL_TREE;
+	      for (unsigned i = 1; i < gimple_switch_num_labels (stmt); ++i)
+		{
+		  tree lab = gimple_switch_label (stmt, i);
+		  basic_block dest = label_to_block (cfun, CASE_LABEL (lab));
+		  edge e2 = find_edge (gimple_bb (stmt), dest);
+		  if (e == e2)
+		    {
+		      tree cmp;
+		      if (CASE_HIGH (lab) != NULL_TREE)
+			{
+			  tree cmp1 = build2 (GE_EXPR, boolean_type_node, idx,
+					      CASE_LOW (lab));
+			  tree cmp2 = build2 (LE_EXPR, boolean_type_node, idx,
+					      CASE_HIGH (lab));
+			  cmp = build2 (BIT_AND_EXPR, boolean_type_node, cmp1,
+					cmp2);
+			}
+		      else
+			cmp = build2 (EQ_EXPR, boolean_type_node, idx,
+				      CASE_LOW (lab));
+
+		      /* Combine the expression with the existing one.  */
+		      if (expr == NULL_TREE)
+			expr = cmp;
+		      else
+			expr = build2 (BIT_IOR_EXPR, boolean_type_node, expr,
+				       cmp);
+		    }
+		}
 
-  return cond;
+	      if (expr != NULL_TREE)
+		{
+		  *cond_edge = e;
+		  return expr;
+		}
+	    }
+	}
+    }
+
+  return NULL_TREE;
 }
 
 /* Simplifies COND using checks in front of the entry of the LOOP.  Just very
@@ -269,6 +344,7 @@ tree_unswitch_single_loop (class loop *loop, int num)
   class loop *nloop;
   unsigned i, found;
   tree cond = NULL_TREE;
+  edge cond_edge = NULL;
   gimple *stmt;
   bool changed = false;
   HOST_WIDE_INT iterations;
@@ -311,11 +387,12 @@ tree_unswitch_single_loop (class loop *loop, int num)
   bbs = get_loop_body (loop);
   found = loop->num_nodes;
 
+  gimple_ranger ranger;
   while (1)
     {
       /* Find a bb to unswitch on.  */
       for (; i < loop->num_nodes; i++)
-	if ((cond = tree_may_unswitch_on (bbs[i], loop)))
+	if ((cond = tree_may_unswitch_on (bbs[i], loop, &cond_edge)))
 	  break;
 
       if (i == loop->num_nodes)
@@ -333,24 +410,77 @@ tree_unswitch_single_loop (class loop *loop, int num)
 	  break;
 	}
 
-      cond = simplify_using_entry_checks (loop, cond);
       stmt = last_stmt (bbs[i]);
-      if (integer_nonzerop (cond))
+      gcond *condition = dyn_cast<gcond *> (stmt);
+      gswitch *swtch = dyn_cast<gswitch *> (stmt);
+
+      if (condition != NULL)
 	{
-	  /* Remove false path.  */
-	  gimple_cond_set_condition_from_tree (as_a <gcond *> (stmt),
-					       boolean_true_node);
-	  changed = true;
+	  tree result;
+	  int_range_max r;
+
+	  if (ranger.range_of_stmt (r, stmt) && r.singleton_p (&result))
+	    {
+	      gimple_cond_set_condition_from_tree (condition,
+						   result);
+	      update_stmt (condition);
+	      changed = true;
+	    }
+	  else
+	    {
+	      /* FIXME: Remove legacy code for floating point type that
+		 is currently not supported by ranger.  */
+	      cond = simplify_using_entry_checks (loop, cond);
+	      if (integer_nonzerop (cond))
+		{
+		  gimple_cond_set_condition_from_tree (condition,
+						       boolean_true_node);
+		  update_stmt (condition);
+		  changed = true;
+		}
+	      else if (integer_zerop (cond))
+		{
+		  /* Remove true path.  */
+		  gimple_cond_set_condition_from_tree (condition,
+						       boolean_false_node);
+		  update_stmt (condition);
+		  changed = true;
+		}
+	    }
 	}
-      else if (integer_zerop (cond))
+      else if (swtch != NULL)
 	{
-	  /* Remove true path.  */
-	  gimple_cond_set_condition_from_tree (as_a <gcond *> (stmt),
-					       boolean_false_node);
-	  changed = true;
+	  hash_set<edge> ignored_edges;
+	  unsigned nlabels = gimple_switch_num_labels (swtch);
+	  tree index_candidate = NULL_TREE;
+
+	  for (unsigned i = 0; i < nlabels; ++i)
+	    {
+	      tree lab = gimple_switch_label (swtch, i);
+	      basic_block dest = label_to_block (cfun, CASE_LABEL (lab));
+	      edge e = find_edge (gimple_bb (stmt), dest);
+
+	      int_range_max r;
+	      if (ranger.range_on_edge (r, e, gimple_switch_index (swtch))
+		  && r.undefined_p ())
+		{
+		  e->flags |= EDGE_IGNORE;
+		  ignored_edges.add (e);
+		}
+	      else
+		index_candidate = CASE_LOW (lab);
+	    }
+
+	  if (index_candidate != NULL_TREE
+	      && ignored_edges.elements () == EDGE_COUNT (bbs[i]->succs) - 1)
+	    {
+	      gimple_switch_set_index (swtch, index_candidate);
+	      update_stmt (swtch);
+	    }
 	}
+
       /* Do not unswitch too much.  */
-      else if (num > param_max_unswitch_level)
+      if (num > param_max_unswitch_level)
 	{
 	  i++;
 	  continue;
@@ -371,7 +501,6 @@ tree_unswitch_single_loop (class loop *loop, int num)
 	  break;
 	}
 
-      update_stmt (stmt);
       i++;
     }
 
@@ -435,7 +564,7 @@ tree_unswitch_single_loop (class loop *loop, int num)
       /* Find a bb to unswitch on.  */
       for (; found < loop->num_nodes; found++)
 	if ((bbs[found]->flags & BB_REACHABLE)
-	    && (cond = tree_may_unswitch_on (bbs[found], loop)))
+	    && (cond = tree_may_unswitch_on (bbs[found], loop, &cond_edge)))
 	  break;
 
       if (found == loop->num_nodes)
@@ -446,11 +575,15 @@ tree_unswitch_single_loop (class loop *loop, int num)
     }
 
   if (dump_file && (dump_flags & TDF_DETAILS))
-    fprintf (dump_file, ";; Unswitching loop\n");
+    {
+      fprintf (dump_file, ";; Unswitching loop with condition: ");
+      print_generic_expr (dump_file, cond);
+      fprintf (dump_file, "\n");
+    }
 
   initialize_original_copy_tables ();
   /* Unswitch the loop on this condition.  */
-  nloop = tree_unswitch_loop (loop, bbs[found], cond);
+  nloop = tree_unswitch_loop (loop, bbs[found], cond, cond_edge);
   if (!nloop)
     {
       free_original_copy_tables ();
@@ -476,18 +609,15 @@ tree_unswitch_single_loop (class loop *loop, int num)
 
 static class loop *
 tree_unswitch_loop (class loop *loop,
-		    basic_block unswitch_on, tree cond)
+		    basic_block unswitch_on, tree cond, edge cond_edge)
 {
   profile_probability prob_true;
-  edge edge_true, edge_false;
 
   /* Some sanity checking.  */
   gcc_assert (flow_bb_inside_loop_p (loop, unswitch_on));
-  gcc_assert (EDGE_COUNT (unswitch_on->succs) == 2);
   gcc_assert (loop->inner == NULL);
 
-  extract_true_false_edges_from_block (unswitch_on, &edge_true, &edge_false);
-  prob_true = edge_true->probability;
+  prob_true = cond_edge->probability;
   return loop_version (loop, unshare_expr (cond),
 		       NULL, prob_true,
 		       prob_true.invert (),
@@ -965,6 +1095,42 @@ check_exit_phi (class loop *loop)
   return true;
 }
 
+/* Remove all dead cases from switches that are unswitched.  */
+
+static void
+clean_up_switches (void)
+{
+  basic_block bb;
+
+  FOR_EACH_BB_FN (bb, cfun)
+    {
+      gimple *last = last_stmt (bb);
+      if (gswitch *stmt = safe_dyn_cast <gswitch *> (last))
+	{
+	  unsigned nlabels = gimple_switch_num_labels (stmt);
+	  unsigned index = 1;
+	  for (unsigned i = 1; i < nlabels; ++i)
+	    {
+	      tree lab = gimple_switch_label (stmt, i);
+	      basic_block dest = label_to_block (cfun, CASE_LABEL (lab));
+	      edge e = find_edge (gimple_bb (stmt), dest);
+	      if (e == NULL)
+		; /* The edge is already removed.  */
+	      else if (e->flags & EDGE_IGNORE)
+		remove_edge (e);
+	      else
+		{
+		  gimple_switch_set_label (stmt, index, lab);
+		  ++index;
+		}
+	    }
+
+	  if (index != nlabels)
+	    gimple_switch_set_num_labels (stmt, index);
+	}
+    }
+}
+
 /* Loop unswitching pass.  */
 
 namespace {