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[PATCH] Teach VRP to register assertions along default switch labels (PR 18046)


This patch teaches VRP to register along a default switch label
assertions that corresponds to the anti range of each case label.

Does this look OK to commit after bootstrap + regtest on
x86_64-pc-linux-gnu?
---
 gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-6.c |  2 +-
 gcc/testsuite/gcc.dg/tree-ssa/vrp103.c           | 30 ++++++++++++++++++
 gcc/testsuite/gcc.dg/tree-ssa/vrp104.c           | 32 +++++++++++++++++++
 gcc/tree-vrp.c                                   | 39 ++++++++++++++++++++++--
 4 files changed, 100 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/vrp103.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/vrp104.c

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-6.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-6.c
index 5ec4687..551fbac 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-6.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-6.c
@@ -1,7 +1,7 @@
 /* { dg-do compile } */
 /* { dg-options "-O2 -fdump-tree-thread1-details -fdump-tree-thread2-details" } */
 /* { dg-final { scan-tree-dump-times "FSM" 3 "thread1" } } */
-/* { dg-final { scan-tree-dump-times "FSM" 4 "thread2" } } */
+/* { dg-final { scan-tree-dump-times "FSM" 5 "thread2" } } */
 
 int sum0, sum1, sum2, sum3;
 int foo (char *s, char **ret)
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp103.c b/gcc/testsuite/gcc.dg/tree-ssa/vrp103.c
new file mode 100644
index 0000000..eea98bb
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp103.c
@@ -0,0 +1,30 @@
+/* PR tree-optimization/18046  */
+/* { dg-options "-O2 -fdump-tree-vrp" }  */
+/* { dg-final { scan-tree-dump-times "baz \\(0\\);" 4 "vrp1" } }  */
+
+void foo ();
+void bar ();
+void baz (int);
+
+void
+test (int i)
+{
+  switch (i)
+    {
+    case 1:
+    case 2:
+    case 3:
+      foo ();
+      break;
+    case 5:
+      bar ();
+      break;
+    default:
+      /* These tests should be folded to 0, resulting in 4 calls to bar (0).  */
+      baz (i == 1);
+      baz (i == 2);
+      baz (i == 3);
+      baz (i == 5);
+      break;
+    }
+}
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp104.c b/gcc/testsuite/gcc.dg/tree-ssa/vrp104.c
new file mode 100644
index 0000000..6410847
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp104.c
@@ -0,0 +1,32 @@
+/* PR tree-optimization/18046  */
+/* { dg-options "-O2 -fdump-tree-optimized" }  */
+/* { dg-final { scan-tree-dump-times "switch" 1 "optimized" } }  */
+
+void foo ();
+void bar ();
+
+void
+test (int i)
+{
+  switch (i)
+    {
+    case 1:
+      foo ();
+      break;
+    case 2:
+      bar ();
+      break;
+    default:
+      break;
+    }
+
+  /* This switch should be gone after threading/VRP.  */
+  switch (i)
+    {
+    case 1:
+      foo ();
+      break;
+    default:
+      break;
+    }
+}
diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index 06364b7..32a4de3 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -5917,6 +5917,7 @@ find_switch_asserts (basic_block bb, gswitch *last)
       ci[idx].expr = gimple_switch_label (last, idx);
       ci[idx].bb = label_to_block (CASE_LABEL (ci[idx].expr));
     }
+  edge default_edge = find_edge (bb, ci[0].bb);
   qsort (ci, n, sizeof (struct case_info), compare_case_labels);
 
   for (idx = 0; idx < n; ++idx)
@@ -5945,8 +5946,8 @@ find_switch_asserts (basic_block bb, gswitch *last)
 	    max = CASE_LOW (ci[idx].expr);
 	}
 
-      /* Nothing to do if the range includes the default label until we
-	 can register anti-ranges.  */
+      /* Can't extract a useful assertion out of a range that includes the
+         default label.  */
       if (min == NULL_TREE)
 	continue;
 
@@ -5963,6 +5964,40 @@ find_switch_asserts (basic_block bb, gswitch *last)
 				  fold_convert (TREE_TYPE (op), max));
     }
 
+  /* For each case label, register along the default label an assertion that
+     corresponds to the anti-range of that label.  */
+  for (idx = 0; idx < n; ++idx)
+    {
+      tree min, max;
+      tree cl = ci[idx].expr;
+
+      min = CASE_LOW (cl);
+      max = CASE_HIGH (cl);
+
+      if (min == NULL_TREE)
+	continue;
+
+      if (max == NULL_TREE)
+	{
+	  /* Register the assertion OP != MIN.  */
+	  min = fold_convert (TREE_TYPE (op), min);
+	  register_edge_assert_for (op, default_edge, bsi, NE_EXPR, op, min);
+	}
+      else
+	{
+	  /* Register the assertion (unsigned)OP - MIN > (MAX - MIN),
+	     which will give OP the anti-range ~[MIN,MAX].  */
+	  tree uop = fold_convert (unsigned_type_for (TREE_TYPE (op)), op);
+	  min = fold_convert (TREE_TYPE (uop), min);
+	  max = fold_convert (TREE_TYPE (uop), max);
+
+	  tree lhs = fold_build2 (MINUS_EXPR, TREE_TYPE (uop), uop, min);
+	  tree rhs = int_const_binop (MINUS_EXPR, max, min);
+	  register_new_assert_for (op, lhs, GT_EXPR, rhs,
+				   NULL, default_edge, bsi);
+	}
+    }
+
   XDELETEVEC (ci);
 }
 
-- 
2.9.2.413.g76d2a70


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