[PATCH] Fix thinko in early bail out in tree-switch-conversion.

[Martin Liška]

Hi.

Thanks to Jakub, the patch addresses one memory leak in
bit_test_cluster::find_bit_tests (allocation of output).
And moreover, it implements proper guard when clustering
is not successful. In such situation we want a quick bail out.

Patch can bootstrap on x86_64-linux-gnu and survives regression tests.

Ready to be installed?
Thanks,
Martin

gcc/ChangeLog:

2019-08-29  Martin Liska  <mli...@suse.cz>

        * tree-switch-conversion.c (jump_table_cluster::find_jump_tables):
        Bail out when we'll end up with the same number of clusters as
        at the beginning.
        (bit_test_cluster::find_bit_tests): Likewise for bit tests.
        (jump_table_cluster::can_be_handled): Remove the guard
        as it's already handled in ::is_enabled.  Allocate output
        after early bail out.
---
 gcc/tree-switch-conversion.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)



diff --git a/gcc/tree-switch-conversion.c b/gcc/tree-switch-conversion.c
index 776db77f53a..988e923d7e8 100644
--- a/gcc/tree-switch-conversion.c
+++ b/gcc/tree-switch-conversion.c
@@ -1213,14 +1213,14 @@ jump_table_cluster::find_jump_tables (vec<cluster *> &clusters)
     }
 
   /* No result.  */
-  if (min[l].m_count == INT_MAX)
+  if (min[l].m_count == l)
     return clusters.copy ();
 
   vec<cluster *> output;
   output.create (4);
 
   /* Find and build the clusters.  */
-  for (int end = l;;)
+  for (unsigned int end = l;;)
     {
       int start = min[end].m_start;
 
@@ -1257,11 +1257,9 @@ jump_table_cluster::can_be_handled (const vec<cluster *> &clusters,
      make a sequence of conditional branches instead of a dispatch.
 
      The definition of "much bigger" depends on whether we are
-     optimizing for size or for speed.  */
-  if (!flag_jump_tables)
-    return false;
+     optimizing for size or for speed.
 
-  /* For algorithm correctness, jump table for a single case must return
+     For algorithm correctness, jump table for a single case must return
      true.  We bail out in is_beneficial if it's called just for
      a single case.  */
   if (start == end)
@@ -1311,9 +1309,6 @@ jump_table_cluster::is_beneficial (const vec<cluster *> &,
 vec<cluster *>
 bit_test_cluster::find_bit_tests (vec<cluster *> &clusters)
 {
-  vec<cluster *> output;
-  output.create (4);
-
   unsigned l = clusters.length ();
   auto_vec<min_cluster_item> min;
   min.reserve (l + 1);
@@ -1336,9 +1331,12 @@ bit_test_cluster::find_bit_tests (vec<cluster *> &clusters)
     }
 
   /* No result.  */
-  if (min[l].m_count == INT_MAX)
+  if (min[l].m_count == l)
     return clusters.copy ();
 
+  vec<cluster *> output;
+  output.create (4);
+
   /* Find and build the clusters.  */
   for (unsigned end = l;;)
     {