[gcc r16-9411] tree-cfg: Revert part of r8-546 [PR125290]

https://gcc.gnu.org/g:8a8b309e0ec8447ad08e3d1c99b3b37e18272f02

commit r16-9411-g8a8b309e0ec8447ad08e3d1c99b3b37e18272f02
Author: Andrew Pinski <[email protected]>
Date:   Wed May 13 21:24:43 2026 -0700

    tree-cfg: Revert part of r8-546 [PR125290]
    
    This reverts the group_case_labels_stmt part of r8-546-gca4d2851687875.
    This is placed in the wrong location to remove the case statements that go
    directly to __builtin_unreachable. In fact the removal of the case statements
    make us lose optimizations in some cases (Wuninitialized-pr107919-1.C for one).
    
    Also this fixes PR 125290 by no longer leaving around a switch which just
    has a default case.
    
    Bootstrapped and tested on x86_64-linux-gnu.
    
            PR tree-optimization/125290
    
    gcc/ChangeLog:
    
            * tree-cfg.cc (group_case_labels_stmt): Remove code that was
            added to remove `cases` that goto blocks of unreachable.
            * tree-ssa-forwprop.cc (optimize_unreachable): Remove the
            comment about switch cases being handled.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/warn/Wuninitialized-pr107919-1.C: Remove xfail.
            * gcc.dg/analyzer/taint-assert.c: Update for the non-removal
            of block containing unreachable.
            * gcc.dg/torture/pr125290-1.c: New test.
    
    Signed-off-by: Andrew Pinski <[email protected]>
    (cherry picked from commit f108e23d2bff50d0ee8cf0d25a08be5432b702b6)

Diff:
---
 .../g++.dg/warn/Wuninitialized-pr107919-1.C        |  2 +-
 gcc/testsuite/gcc.dg/analyzer/taint-assert.c       |  4 +-
 gcc/testsuite/gcc.dg/torture/pr125290-1.c          | 40 +++++++++++++++++
 gcc/tree-cfg.cc                                    | 51 +---------------------
 gcc/tree-ssa-forwprop.cc                           |  3 +-
 5 files changed, 46 insertions(+), 54 deletions(-)

diff --git a/gcc/testsuite/g++.dg/warn/Wuninitialized-pr107919-1.C b/gcc/testsuite/g++.dg/warn/Wuninitialized-pr107919-1.C
index 049fa4d307ae..b3ed4628bdda 100644
--- a/gcc/testsuite/g++.dg/warn/Wuninitialized-pr107919-1.C
+++ b/gcc/testsuite/g++.dg/warn/Wuninitialized-pr107919-1.C
@@ -14,4 +14,4 @@ void do_something(void* storage)
   std::swap(event, swappedValue);
 }
 
-// { dg-bogus "may be used uninitialized" "" { xfail *-*-* } 0 }
+// { dg-bogus "may be used uninitialized" "" 0 }
diff --git a/gcc/testsuite/gcc.dg/analyzer/taint-assert.c b/gcc/testsuite/gcc.dg/analyzer/taint-assert.c
index a858e996a801..e46cbe95801d 100644
--- a/gcc/testsuite/gcc.dg/analyzer/taint-assert.c
+++ b/gcc/testsuite/gcc.dg/analyzer/taint-assert.c
@@ -322,8 +322,8 @@ test_switch_bogus_case_unreachable (int n)
     case 2:
       return -1;
     case 42:
-      /* This case gets optimized away before we see it.  */
-      __builtin_unreachable ();
+      /* The wording is rather inaccurate here.  */
+      __builtin_unreachable (); /* { dg-warning "use of attacked-controlled value in condition for assertion" } */
     }
 }
 
diff --git a/gcc/testsuite/gcc.dg/torture/pr125290-1.c b/gcc/testsuite/gcc.dg/torture/pr125290-1.c
new file mode 100644
index 000000000000..6183cbd26819
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr125290-1.c
@@ -0,0 +1,40 @@
+/* PR tree-optimization/125290 */
+/* { dg-do compile } */
+
+int g21;
+int g31, f14f16_c12;
+void f14f16()
+{
+    short v7;
+    long v9;
+    long v13;
+    if (g31)
+    {
+        g21 = 0;
+        switch (v7)
+        {
+            case 4:
+            case 66: break;
+            default: __builtin_unreachable();
+        }
+    }
+    else
+    {
+    lbl_bf2:
+        v9 = g21;
+    }
+    v13 = v9;
+    switch (v13)
+    {
+        case 55:
+        case 2: goto lbl_sw12;
+        default:
+            if (f14f16_c12)
+                goto lbl_bf2;
+            else
+                return;
+    }
+lbl_sw12:
+    __builtin_unreachable();
+}
+
diff --git a/gcc/tree-cfg.cc b/gcc/tree-cfg.cc
index e42e22cf769f..51858d9f2655 100644
--- a/gcc/tree-cfg.cc
+++ b/gcc/tree-cfg.cc
@@ -1712,7 +1712,6 @@ group_case_labels_stmt (gswitch *stmt)
   int old_size = gimple_switch_num_labels (stmt);
   int i, next_index, new_size;
   basic_block default_bb = NULL;
-  hash_set<tree> *removed_labels = NULL;
 
   default_bb = gimple_switch_default_bb (cfun, stmt);
 
@@ -1728,12 +1727,9 @@ group_case_labels_stmt (gswitch *stmt)
       gcc_assert (base_case);
       base_bb = label_to_block (cfun, CASE_LABEL (base_case));
 
-      /* Discard cases that have the same destination as the default case or
-	 whose destination blocks have already been removed as unreachable.  */
+      /* Discard cases that have the same destination as the default case.  */
       if (base_bb == NULL
-	  || base_bb == default_bb
-	  || (removed_labels
-	      && removed_labels->contains (CASE_LABEL (base_case))))
+	  || base_bb == default_bb)
 	{
 	  i++;
 	  continue;
@@ -1756,8 +1752,6 @@ group_case_labels_stmt (gswitch *stmt)
 	  /* Merge the cases if they jump to the same place,
 	     and their ranges are consecutive.  */
 	  if (merge_bb == base_bb
-	      && (removed_labels == NULL
-		  || !removed_labels->contains (CASE_LABEL (merge_case)))
 	      && wi::to_wide (CASE_LOW (merge_case)) == bhp1)
 	    {
 	      base_high
@@ -1770,46 +1764,6 @@ group_case_labels_stmt (gswitch *stmt)
 	    break;
 	}
 
-      /* Discard cases that have an unreachable destination block.  */
-      if (EDGE_COUNT (base_bb->succs) == 0
-	  && gimple_seq_unreachable_p (bb_seq (base_bb))
-	  /* Don't optimize this if __builtin_unreachable () is the
-	     implicitly added one by the C++ FE too early, before
-	     -Wreturn-type can be diagnosed.  We'll optimize it later
-	     during switchconv pass or any other cfg cleanup.  */
-	  && (gimple_in_ssa_p (cfun)
-	      || (LOCATION_LOCUS (gimple_location (last_nondebug_stmt (base_bb)))
-		  != BUILTINS_LOCATION)))
-	{
-	  edge base_edge = find_edge (gimple_bb (stmt), base_bb);
-	  if (base_edge != NULL)
-	    {
-	      for (gimple_stmt_iterator gsi = gsi_start_bb (base_bb);
-		   !gsi_end_p (gsi); gsi_next (&gsi))
-		if (glabel *stmt = dyn_cast <glabel *> (gsi_stmt (gsi)))
-		  {
-		    if (FORCED_LABEL (gimple_label_label (stmt))
-			|| DECL_NONLOCAL (gimple_label_label (stmt)))
-		      {
-			/* Forced/non-local labels aren't going to be removed,
-			   but they will be moved to some neighbouring basic
-			   block. If some later case label refers to one of
-			   those labels, we should throw that case away rather
-			   than keeping it around and referring to some random
-			   other basic block without an edge to it.  */
-			if (removed_labels == NULL)
-			  removed_labels = new hash_set<tree>;
-			removed_labels->add (gimple_label_label (stmt));
-		      }
-		  }
-		else
-		  break;
-	      remove_edge_and_dominated_blocks (base_edge);
-	    }
-	  i = next_index;
-	  continue;
-	}
-
       if (new_size < i)
 	gimple_switch_set_label (stmt, new_size,
 				 gimple_switch_label (stmt, i));
@@ -1822,7 +1776,6 @@ group_case_labels_stmt (gswitch *stmt)
   if (new_size < old_size)
     gimple_switch_set_num_labels (stmt, new_size);
 
-  delete removed_labels;
   return new_size < old_size;
 }
 
diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index 6b745382fa0e..ce8bd0e0599d 100644
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -5258,8 +5258,7 @@ optimize_unreachable (basic_block bb)
 	}
       else
 	{
-	  /* Todo: handle other cases.  Note that unreachable switch case
-	     statements have already been removed.  */
+	  /* Todo: handle other cases.  e.g. switch.  */
 	  continue;
 	}