Re: [PATCH] middle-end/93519 - avoid folding stmts in obviously unreachable code

[Richard Biener <rguenther@suse.de>]

On Thu, 6 Feb 2020, Martin Sebor wrote:

> On 2/6/20 7:52 AM, Richard Biener wrote:
> > The inliner folds stmts delayed, the following arranges things so
> > to not fold stmts that are obviously not reachable to avoid warnings
> > from those code regions.
> > 
> > Bootstrapped and tested on x86_64-unknown-linux-gnu.
> 
> It fixes the reported problem so it works for me.
> 
> The tests I submitted with my patch fail a number of cases because
> along with strcpy it also deferred folding overlapping mempcpy calls.
> That was not strictly part of the regression so I'm okay with deferring
> it until GCC 11.  I will resubmit an updated patch to defer the folding
> then.

The following is what I have applied, fixing the quadraticness with
switch stmt edges, trading it with possible re-allocation of the
worker stack.

Bootstrapped and tested on x86_64-unknown-linux-gnu.

Richard.

From ed41d9926a45d5ebc50d3721dde564cabd36f861 Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Thu, 6 Feb 2020 15:49:57 +0100
Subject: [PATCH] middle-end/93519 - avoid folding stmts in obviously
 unreachable code

The inliner folds stmts delayed, the following arranges things so
to not fold stmts that are obviously not reachable to avoid warnings
from those code regions.

2020-02-06  Richard Biener  <rguenther@suse.de>

	PR middle-end/93519
	* tree-inline.c (fold_marked_statements): Do a PRE walk,
	skipping unreachable regions.
	(optimize_inline_calls): Skip folding stmts when we didn't
	inline.

	* gcc.dg/Wrestrict-21.c: New testcase.

diff --git a/gcc/testsuite/gcc.dg/Wrestrict-21.c b/gcc/testsuite/gcc.dg/Wrestrict-21.c
new file mode 100644
index 00000000000..e300663758e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wrestrict-21.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wrestrict" } */
+
+static char *
+str_numth(char *dest, char *num, int type)
+{
+  if (dest != num)
+    __builtin_strcpy(dest, num); /* { dg-bogus "is the same" } */
+  __builtin_strcat(dest, "foo");
+  return dest;
+}
+
+void
+DCH_to_char(char *in, char *out, int collid)
+{
+  char *s = out;
+  str_numth(s, s, 42);
+}
diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c
index 5b0050a53d2..23941dade55 100644
--- a/gcc/tree-inline.c
+++ b/gcc/tree-inline.c
@@ -5261,86 +5261,117 @@ static void
 fold_marked_statements (int first, hash_set<gimple *> *statements)
 {
   auto_bitmap to_purge;
-  for (; first < last_basic_block_for_fn (cfun); first++)
-    if (BASIC_BLOCK_FOR_FN (cfun, first))
-      {
-        gimple_stmt_iterator gsi;
 
-	for (gsi = gsi_start_bb (BASIC_BLOCK_FOR_FN (cfun, first));
-	     !gsi_end_p (gsi);
-	     gsi_next (&gsi))
-	  if (statements->contains (gsi_stmt (gsi)))
-	    {
-	      gimple *old_stmt = gsi_stmt (gsi);
-	      tree old_decl
-		= is_gimple_call (old_stmt) ? gimple_call_fndecl (old_stmt) : 0;
+  auto_vec<edge, 20> stack (n_basic_blocks_for_fn (cfun) + 2);
+  auto_sbitmap visited (last_basic_block_for_fn (cfun));
+  bitmap_clear (visited);
 
-	      if (old_decl && fndecl_built_in_p (old_decl))
-		{
-		  /* Folding builtins can create multiple instructions,
-		     we need to look at all of them.  */
-		  gimple_stmt_iterator i2 = gsi;
-		  gsi_prev (&i2);
-		  if (fold_stmt (&gsi))
-		    {
-		      gimple *new_stmt;
-		      /* If a builtin at the end of a bb folded into nothing,
-			 the following loop won't work.  */
-		      if (gsi_end_p (gsi))
-			{
-			  cgraph_update_edges_for_call_stmt (old_stmt,
-							     old_decl, NULL);
-			  break;
-			}
-		      if (gsi_end_p (i2))
-			i2 = gsi_start_bb (BASIC_BLOCK_FOR_FN (cfun, first));
-		      else
+  stack.quick_push (single_succ_edge (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
+  while (!stack.is_empty ())
+    {
+      /* Look at the edge on the top of the stack.  */
+      edge e = stack.pop ();
+      basic_block dest = e->dest;
+
+      if (dest == EXIT_BLOCK_PTR_FOR_FN (cfun)
+	  || bitmap_bit_p (visited, dest->index))
+	continue;
+
+      bitmap_set_bit (visited, dest->index);
+
+      if (dest->index >= first)
+	for (gimple_stmt_iterator gsi = gsi_start_bb (dest);
+	     !gsi_end_p (gsi); gsi_next (&gsi))
+	  {
+	    if (!statements->contains (gsi_stmt (gsi)))
+	      continue;
+
+	    gimple *old_stmt = gsi_stmt (gsi);
+	    tree old_decl = (is_gimple_call (old_stmt)
+			     ? gimple_call_fndecl (old_stmt) : 0);
+	    if (old_decl && fndecl_built_in_p (old_decl))
+	      {
+		/* Folding builtins can create multiple instructions,
+		   we need to look at all of them.  */
+		gimple_stmt_iterator i2 = gsi;
+		gsi_prev (&i2);
+		if (fold_stmt (&gsi))
+		  {
+		    gimple *new_stmt;
+		    /* If a builtin at the end of a bb folded into nothing,
+		       the following loop won't work.  */
+		    if (gsi_end_p (gsi))
+		      {
+			cgraph_update_edges_for_call_stmt (old_stmt,
+							   old_decl, NULL);
+			break;
+		      }
+		    if (gsi_end_p (i2))
+		      i2 = gsi_start_bb (dest);
+		    else
+		      gsi_next (&i2);
+		    while (1)
+		      {
+			new_stmt = gsi_stmt (i2);
+			update_stmt (new_stmt);
+			cgraph_update_edges_for_call_stmt (old_stmt, old_decl,
+							   new_stmt);
+
+			if (new_stmt == gsi_stmt (gsi))
+			  {
+			    /* It is okay to check only for the very last
+			       of these statements.  If it is a throwing
+			       statement nothing will change.  If it isn't
+			       this can remove EH edges.  If that weren't
+			       correct then because some intermediate stmts
+			       throw, but not the last one.  That would mean
+			       we'd have to split the block, which we can't
+			       here and we'd loose anyway.  And as builtins
+			       probably never throw, this all
+			       is mood anyway.  */
+			    if (maybe_clean_or_replace_eh_stmt (old_stmt,
+								new_stmt))
+			      bitmap_set_bit (to_purge, dest->index);
+			    break;
+			  }
 			gsi_next (&i2);
-		      while (1)
-			{
-			  new_stmt = gsi_stmt (i2);
-			  update_stmt (new_stmt);
-			  cgraph_update_edges_for_call_stmt (old_stmt, old_decl,
-							     new_stmt);
+		      }
+		  }
+	      }
+	    else if (fold_stmt (&gsi))
+	      {
+		/* Re-read the statement from GSI as fold_stmt() may
+		   have changed it.  */
+		gimple *new_stmt = gsi_stmt (gsi);
+		update_stmt (new_stmt);
+
+		if (is_gimple_call (old_stmt)
+		    || is_gimple_call (new_stmt))
+		  cgraph_update_edges_for_call_stmt (old_stmt, old_decl,
+						     new_stmt);
+
+		if (maybe_clean_or_replace_eh_stmt (old_stmt, new_stmt))
+		  bitmap_set_bit (to_purge, dest->index);
+	      }
+	  }
 
-			  if (new_stmt == gsi_stmt (gsi))
-			    {
-			      /* It is okay to check only for the very last
-				 of these statements.  If it is a throwing
-				 statement nothing will change.  If it isn't
-				 this can remove EH edges.  If that weren't
-				 correct then because some intermediate stmts
-				 throw, but not the last one.  That would mean
-				 we'd have to split the block, which we can't
-				 here and we'd loose anyway.  And as builtins
-				 probably never throw, this all
-				 is mood anyway.  */
-			      if (maybe_clean_or_replace_eh_stmt (old_stmt,
-								  new_stmt))
-				bitmap_set_bit (to_purge, first);
-			      break;
-			    }
-			  gsi_next (&i2);
-			}
-		    }
-		}
-	      else if (fold_stmt (&gsi))
-		{
-		  /* Re-read the statement from GSI as fold_stmt() may
-		     have changed it.  */
-		  gimple *new_stmt = gsi_stmt (gsi);
-		  update_stmt (new_stmt);
-
-		  if (is_gimple_call (old_stmt)
-		      || is_gimple_call (new_stmt))
-		    cgraph_update_edges_for_call_stmt (old_stmt, old_decl,
-						       new_stmt);
-
-		  if (maybe_clean_or_replace_eh_stmt (old_stmt, new_stmt))
-		    bitmap_set_bit (to_purge, first);
-		}
+      if (EDGE_COUNT (dest->succs) > 0)
+	{
+	  /* Avoid warnings emitted from folding statements that
+	     became unreachable because of inlined function parameter
+	     propagation.  */
+	  e = find_taken_edge (dest, NULL_TREE);
+	  if (e)
+	    stack.quick_push (e);
+	  else
+	    {
+	      edge_iterator ei;
+	      FOR_EACH_EDGE (e, ei, dest->succs)
+		stack.safe_push (e);
 	    }
-      }
+	}
+    }
+
   gimple_purge_all_dead_eh_edges (to_purge);
 }
 
@@ -5404,6 +5435,13 @@ optimize_inline_calls (tree fn)
 	gcc_assert (e->inline_failed);
     }
 
+  /* If we didn't inline into the function there is nothing to do.  */
+  if (!inlined_p)
+    {
+      delete id.statements_to_fold;
+      return 0;
+    }
+
   /* Fold queued statements.  */
   update_max_bb_count ();
   fold_marked_statements (last, id.statements_to_fold);
@@ -5426,10 +5464,6 @@ optimize_inline_calls (tree fn)
 
   gcc_assert (!id.debug_stmts.exists ());
 
-  /* If we didn't inline into the function there is nothing to do.  */
-  if (!inlined_p)
-    return 0;
-
   /* Renumber the lexical scoping (non-code) blocks consecutively.  */
   number_blocks (fn);