[PATCH] Group switch cases in switch lowering (PR tree-optimization/87205).

[Martin Liška]

Hi.

It's beneficial to group cases before switch lowering machinery
is making a decision what to do with a switch.

Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.

Ready to be installed?
Martin


gcc/ChangeLog:

2018-09-04  Martin Liska  <mli...@suse.cz>

        PR tree-optimization/87205
        * tree-switch-conversion.c (pass_lower_switch::execute):
        Group cases for switch statements.

gcc/testsuite/ChangeLog:

2018-09-04  Martin Liska  <mli...@suse.cz>

        PR tree-optimization/87205
        * gcc.dg/tree-ssa/pr87205-2.c: New test.
        * gcc.dg/tree-ssa/pr87205.c: New test.
---
 gcc/testsuite/gcc.dg/tree-ssa/pr87205-2.c | 18 ++++++++++++++++++
 gcc/testsuite/gcc.dg/tree-ssa/pr87205.c   | 21 +++++++++++++++++++++
 gcc/tree-switch-conversion.c              |  8 ++++++--
 3 files changed, 45 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr87205-2.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr87205.c



diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr87205-2.c b/gcc/testsuite/gcc.dg/tree-ssa/pr87205-2.c
new file mode 100644
index 00000000000..fb1879ed71b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr87205-2.c
@@ -0,0 +1,18 @@
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+void f(int);
+void h(unsigned i)
+{
+  switch (i) {
+    default: __builtin_unreachable();
+    case 0: f(42); break;
+    case 1: f(42); break;
+    case 2: f(42); break;
+    case 3: f(42); break;
+    case 4: f(42); break;
+    case 5: f(42); break;
+  }
+} 
+
+/* { dg-final { scan-tree-dump-not "if" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "switch" "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr87205.c b/gcc/testsuite/gcc.dg/tree-ssa/pr87205.c
new file mode 100644
index 00000000000..129e60747e2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr87205.c
@@ -0,0 +1,21 @@
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+void f( int x );
+
+void h( unsigned ix )
+{
+  switch( ix )
+  {
+    case 0: f(42); break;
+    case 1: f(42); break;
+    case 2: f(42); break;
+    case 3: f(42); break;
+    case 4: f(42); break;
+    case 5: f(42); break;
+    default: __builtin_unreachable();
+  }
+}
+
+
+/* { dg-final { scan-tree-dump-not "if" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "switch" "optimized" } } */
diff --git a/gcc/tree-switch-conversion.c b/gcc/tree-switch-conversion.c
index 1f543b2ecc8..85039e23e58 100644
--- a/gcc/tree-switch-conversion.c
+++ b/gcc/tree-switch-conversion.c
@@ -2419,8 +2419,12 @@ pass_lower_switch<O0>::execute (function *fun)
   FOR_EACH_BB_FN (bb, fun)
     {
       gimple *stmt = last_stmt (bb);
-      if (stmt && gimple_code (stmt) == GIMPLE_SWITCH)
-	switch_statements.safe_push (stmt);
+      gswitch *swtch;
+      if (stmt && (swtch = dyn_cast<gswitch *> (stmt)))
+	{
+	  group_case_labels_stmt (swtch);
+	  switch_statements.safe_push (swtch);
+	}
     }
 
   for (unsigned i = 0; i < switch_statements.length (); i++)