2 files changed, 35 insertions, 2 deletions
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr46555.c b/gcc/testsuite/gcc.dg/tree-ssa/pr46555.c
new file mode 100644
index 0000000..d4de7c2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr46555.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized-details -fdump-rtl-pro_and_epilogue" } */
+/* PR tree-optimization/46555 */
+/* Here should not remove the forwarder block (or rather recreate it and not
+   remove it again). This improves expansion to RTL as there is one less copy
+   (or constant formation) in some cases. In this case we also get the ability
+   to shrink wrap the function.  */
+
+int h(void);
+int f(int a, int b, int c)
+{
+  if (a)
+    return 2;
+  h();
+  if (b)
+    return 2;
+  h();
+  if (c)
+    return 2;
+  h();
+  return 4;
+}
+
+/* { dg-final { scan-tree-dump-times "New forwarder block for edge" 1 "optimized" } } */
+/* Make sure we only have a PHI with 2 arguments here, 2 and 4.  */
+/* { dg-final { scan-tree-dump "PHI <2..., 4...>|PHI <4..., 2...>" "optimized" } } */
+/* Make sure we can shrink wrap the function now too. */
+/* { dg-final { scan-rtl-dump "Performing shrink-wrapping" "pro_and_epilogue" { target { { { i?86-*-* x86_64-*-* } && { ! ia32 } } || { powerpc*-*-* aarch64*-*-* riscv*-*-* arm*-*-* }  } } } } */
diff --git a/gcc/tree-cfgcleanup.cc b/gcc/tree-cfgcleanup.cc
index 872ded3..093fde9 100644
--- a/gcc/tree-cfgcleanup.cc
+++ b/gcc/tree-cfgcleanup.cc
@@ -1415,8 +1415,13 @@ execute_cleanup_cfg_post_optimizing (void)
     }
   maybe_remove_unreachable_handlers ();
   cleanup_dead_labels ();
-  if (group_case_labels ())
-    todo |= TODO_cleanup_cfg;
+  if (group_case_labels () && cleanup_tree_cfg ())
+    todo |= TODO_update_ssa;
+
+  /* When optimizing undo the merging of forwarder blocks
+     that phis for better out of ssa expansion.  */
+  if (optimize)
+    make_forwarders_with_degenerate_phis (cfun);
 
   basic_block bb = single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun));
   gimple_stmt_iterator gsi = gsi_start_nondebug_after_labels_bb (bb);