tree-optimization/104373 - early diagnostic on unreachable code

The following improves early uninit diagnostics by computing edge
reachability using VN and ignoring unreachable blocks when looking
for uninitialized uses.  To not ICE with -fdump-tree-all the
early uninit pass needs a dumpfile since VN tries to dump statistics.

2022-02-04  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/104373
	* tree-ssa-sccvn.h (do_rpo_vn): New export exposing the
	walk kind.
	* tree-ssa-sccvn.cc (do_rpo_vn): Export, get the default
	walk kind as argument.
	(run_rpo_vn): Adjust.
	(pass_fre::execute): Likewise.
	* tree-ssa-uninit.cc (warn_uninitialized_vars): Skip
	blocks not reachable.
	(execute_late_warn_uninitialized): Mark all edges as
	executable.
	(execute_early_warn_uninitialized): Use VN to compute
	executable edges.
	(pass_data_early_warn_uninitialized): Enable a dump file,
	change dump name to warn_uninit.

	* g++.dg/warn/Wuninitialized-32.C: New testcase.
	* gcc.dg/uninit-pr20644-O0.c: Remove XFAIL.

5 files changed, 58 insertions, 16 deletions

diff --git a/gcc/testsuite/g++.dg/warn/Wuninitialized-32.C b/gcc/testsuite/g++.dg/warn/Wuninitialized-32.C
new file mode 100644
index 0000000..8b02b5c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wuninitialized-32.C
@@ -0,0 +1,14 @@
+// { dg-do compile }
+// { dg-additional-options "-Wall" }
+
+void* operator new[](unsigned long, void* __p);
+
+struct allocator
+{
+  ~allocator();
+};
+
+void *foo (void *p)
+{
+  return p ? new(p) allocator[1] : new allocator[1]; // { dg-bogus "uninitialized" }
+}
diff --git a/gcc/testsuite/gcc.dg/uninit-pr20644-O0.c b/gcc/testsuite/gcc.dg/uninit-pr20644-O0.c
index 8ae697a..a335d8c 100644
--- a/gcc/testsuite/gcc.dg/uninit-pr20644-O0.c
+++ b/gcc/testsuite/gcc.dg/uninit-pr20644-O0.c
@@ -7,7 +7,7 @@ int foo ()
   int j;
 
   if (1 == i)
-    return j; /* { dg-bogus "uninitialized" "uninitialized" { xfail *-*-* } } */
+    return j; /* { dg-bogus "uninitialized" "uninitialized" } */
 
   return 0;
 }
diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index a03f0aa..eb17549 100644
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -7034,15 +7034,14 @@ eliminate_with_rpo_vn (bitmap inserted_exprs)
   return walker.eliminate_cleanup ();
 }
 
-static unsigned
+unsigned
 do_rpo_vn (function *fn, edge entry, bitmap exit_bbs,
-	   bool iterate, bool eliminate);
+	   bool iterate, bool eliminate, vn_lookup_kind kind);
 
 void
 run_rpo_vn (vn_lookup_kind kind)
 {
-  default_vn_walk_kind = kind;
-  do_rpo_vn (cfun, NULL, NULL, true, false);
+  do_rpo_vn (cfun, NULL, NULL, true, false, kind);
 
   /* ???  Prune requirement of these.  */
   constant_to_value_id = new hash_table<vn_constant_hasher> (23);
@@ -7740,11 +7739,12 @@ do_unwind (unwind_state *to, rpo_elim &avail)
    executed and iterate.  If ELIMINATE is true then perform
    elimination, otherwise leave that to the caller.  */
 
-static unsigned
+unsigned
 do_rpo_vn (function *fn, edge entry, bitmap exit_bbs,
-	   bool iterate, bool eliminate)
+	   bool iterate, bool eliminate, vn_lookup_kind kind)
 {
   unsigned todo = 0;
+  default_vn_walk_kind = kind;
 
   /* We currently do not support region-based iteration when
      elimination is requested.  */
@@ -8164,8 +8164,7 @@ do_rpo_vn (function *fn, edge entry, bitmap exit_bbs,
 unsigned
 do_rpo_vn (function *fn, edge entry, bitmap exit_bbs)
 {
-  default_vn_walk_kind = VN_WALKREWRITE;
-  unsigned todo = do_rpo_vn (fn, entry, exit_bbs, false, true);
+  unsigned todo = do_rpo_vn (fn, entry, exit_bbs, false, true, VN_WALKREWRITE);
   free_rpo_vn ();
   return todo;
 }
@@ -8221,8 +8220,7 @@ pass_fre::execute (function *fun)
   if (iterate_p)
     loop_optimizer_init (AVOID_CFG_MODIFICATIONS);
 
-  default_vn_walk_kind = VN_WALKREWRITE;
-  todo = do_rpo_vn (fun, NULL, NULL, iterate_p, true);
+  todo = do_rpo_vn (fun, NULL, NULL, iterate_p, true, VN_WALKREWRITE);
   free_rpo_vn ();
 
   if (iterate_p)
diff --git a/gcc/tree-ssa-sccvn.h b/gcc/tree-ssa-sccvn.h
index f161b80..aeed070 100644
--- a/gcc/tree-ssa-sccvn.h
+++ b/gcc/tree-ssa-sccvn.h
@@ -291,6 +291,7 @@ value_id_constant_p (unsigned int v)
 tree fully_constant_vn_reference_p (vn_reference_t);
 tree vn_nary_simplify (vn_nary_op_t);
 
+unsigned do_rpo_vn (function *, edge, bitmap, bool, bool, vn_lookup_kind);
 unsigned do_rpo_vn (function *, edge, bitmap);
 void run_rpo_vn (vn_lookup_kind);
 unsigned eliminate_with_rpo_vn (bitmap);
diff --git a/gcc/tree-ssa-uninit.cc b/gcc/tree-ssa-uninit.cc
index 02e88d5..ab83a4b 100644
--- a/gcc/tree-ssa-uninit.cc
+++ b/gcc/tree-ssa-uninit.cc
@@ -38,8 +38,9 @@ along with GCC; see the file COPYING3.  If not see
 #include "builtins.h"
 #include "calls.h"
 #include "gimple-range.h"
-
 #include "gimple-predicate-analysis.h"
+#include "domwalk.h"
+#include "tree-ssa-sccvn.h"
 
 /* This implements the pass that does predicate aware warning on uses of
    possibly uninitialized variables.  The pass first collects the set of
@@ -986,7 +987,19 @@ warn_uninitialized_vars (bool wmaybe_uninit)
   basic_block bb;
   FOR_EACH_BB_FN (bb, cfun)
     {
+      edge_iterator ei;
+      edge e;
+      FOR_EACH_EDGE (e, ei, bb->preds)
+	if (e->flags & EDGE_EXECUTABLE)
+	  break;
+      /* Skip unreachable blocks.  For early analysis we use VN to
+	 determine edge executability when wmaybe_uninit.  */
+      if (!e)
+	continue;
+
       basic_block succ = single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun));
+      /* ???  This could be improved when we use a greedy walk and have
+	 some edges marked as not executable.  */
       wlims.always_executed = dominated_by_p (CDI_POST_DOMINATORS, succ, bb);
 
       if (wlims.always_executed)
@@ -1319,6 +1332,11 @@ execute_late_warn_uninitialized (function *fun)
 
   calculate_dominance_info (CDI_DOMINATORS);
   calculate_dominance_info (CDI_POST_DOMINATORS);
+
+  /* Mark all edges executable, warn_uninitialized_vars will skip
+     unreachable blocks.  */
+  set_all_edges_as_executable (fun);
+
   /* Re-do the plain uninitialized variable check, as optimization may have
      straightened control flow.  Do this first so that we don't accidentally
      get a "may be" warning when we'd have seen an "is" warning later.  */
@@ -1388,7 +1406,7 @@ make_pass_late_warn_uninitialized (gcc::context *ctxt)
 }
 
 static unsigned int
-execute_early_warn_uninitialized (void)
+execute_early_warn_uninitialized (struct function *fun)
 {
   /* Currently, this pass runs always but
      execute_late_warn_uninitialized only runs with optimization.  With
@@ -1398,6 +1416,17 @@ execute_early_warn_uninitialized (void)
   calculate_dominance_info (CDI_DOMINATORS);
   calculate_dominance_info (CDI_POST_DOMINATORS);
 
+  /* Use VN in its cheapest incarnation and without doing any
+     elimination to compute edge reachability.  Don't bother when
+     we only warn for unconditionally executed code though.  */
+  if (!optimize)
+    {
+      do_rpo_vn (fun, NULL, NULL, false, false, VN_NOWALK);
+      free_rpo_vn ();
+    }
+  else
+    set_all_edges_as_executable (fun);
+
   warn_uninitialized_vars (/*warn_maybe_uninitialized=*/!optimize);
 
   /* Post-dominator information cannot be reliably updated.  Free it
@@ -1412,7 +1441,7 @@ namespace {
 const pass_data pass_data_early_warn_uninitialized =
 {
   GIMPLE_PASS, /* type */
-  "*early_warn_uninitialized", /* name */
+  "early_uninit", /* name */
   OPTGROUP_NONE, /* optinfo_flags */
   TV_TREE_UNINIT, /* tv_id */
   PROP_ssa, /* properties_required */
@@ -1431,9 +1460,9 @@ public:
 
   /* opt_pass methods: */
   virtual bool gate (function *) { return gate_warn_uninitialized (); }
-  virtual unsigned int execute (function *)
+  virtual unsigned int execute (function *fun)
   {
-    return execute_early_warn_uninitialized ();
+    return execute_early_warn_uninitialized (fun);
   }
 
 }; // class pass_early_warn_uninitialized