[PATCH] Fix PR80776

[Richard Biener <rguenther@suse.de>]

The following avoids -Wformat-overflow false positives by teaching
EVRP the trick about __builtin_unreachable () "other" edges and
attaching range info to SSA names.  EVRP does a better job in keeping
ranges for every SSA name from conditional info (VRP "optimizes" its
costly ASSERT_EXPR insertion process).

Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

This will also fix the testcase from PR83072 but it doesn't really
fix all cases I want to fix with a fix for it.  OTOH it might be
this is enough for stage3.

Richard.

2017-11-27  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/80776
	* gimple-ssa-evrp-analyze.h (evrp_range_analyzer::set_ssa_range_info):
	Declare.
	* gimple-ssa-evrp-analyze.c (evrp_range_analyzer::set_ssa_range_info):
	New function.
	(evrp_range_analyzer::record_ranges_from_incoming_edges):
	If the incoming edge is an effective fallthru because the other
	edge only reaches a __builtin_unreachable () then record ranges
	derived from the controlling condition in SSA info.
	(evrp_range_analyzer::record_ranges_from_phis): Use set_ssa_range_info.
	(evrp_range_analyzer::record_ranges_from_stmt): Likewise.

	* gcc.dg/pr80776-1.c: New testcase.
	* gcc.dg/pr80776-2.c: Likewise.

Index: gcc/gimple-ssa-evrp-analyze.c
===================================================================
--- gcc/gimple-ssa-evrp-analyze.c	(revision 255163)
+++ gcc/gimple-ssa-evrp-analyze.c	(working copy)
@@ -91,6 +91,31 @@ evrp_range_analyzer::try_find_new_range
   return NULL;
 }
 
+/* For LHS record VR in the SSA info.  */
+void
+evrp_range_analyzer::set_ssa_range_info (tree lhs, value_range *vr)
+{
+  /* Set the SSA with the value range.  */
+  if (INTEGRAL_TYPE_P (TREE_TYPE (lhs)))
+    {
+      if ((vr->type == VR_RANGE
+	   || vr->type == VR_ANTI_RANGE)
+	  && (TREE_CODE (vr->min) == INTEGER_CST)
+	  && (TREE_CODE (vr->max) == INTEGER_CST))
+	set_range_info (lhs, vr->type,
+			wi::to_wide (vr->min),
+			wi::to_wide (vr->max));
+    }
+  else if (POINTER_TYPE_P (TREE_TYPE (lhs))
+	   && ((vr->type == VR_RANGE
+		&& range_includes_zero_p (vr->min,
+					  vr->max) == 0)
+	       || (vr->type == VR_ANTI_RANGE
+		   && range_includes_zero_p (vr->min,
+					     vr->max) == 1)))
+    set_ptr_nonnull (lhs);
+}
+
 void
 evrp_range_analyzer::record_ranges_from_incoming_edge (basic_block bb)
 {
@@ -134,10 +159,19 @@ evrp_range_analyzer::record_ranges_from_
 	      if (vr)
 		vrs.safe_push (std::make_pair (asserts[i].name, vr));
 	    }
+
+	  /* If pred_e is really a fallthru we can record value ranges
+	     in SSA names as well.  */
+	  bool is_fallthru = assert_unreachable_fallthru_edge_p (pred_e);
+
 	  /* Push updated ranges only after finding all of them to avoid
 	     ordering issues that can lead to worse ranges.  */
 	  for (unsigned i = 0; i < vrs.length (); ++i)
-	    push_value_range (vrs[i].first, vrs[i].second);
+	    {
+	      push_value_range (vrs[i].first, vrs[i].second);
+	      if (is_fallthru)
+		set_ssa_range_info (vrs[i].first, vrs[i].second);
+	    }
 	}
     }
 }
@@ -185,24 +219,7 @@ evrp_range_analyzer::record_ranges_from_
       vr_values->update_value_range (lhs, &vr_result);
 
       /* Set the SSA with the value range.  */
-      if (INTEGRAL_TYPE_P (TREE_TYPE (lhs)))
-	{
-	  if ((vr_result.type == VR_RANGE
-	       || vr_result.type == VR_ANTI_RANGE)
-	      && (TREE_CODE (vr_result.min) == INTEGER_CST)
-	      && (TREE_CODE (vr_result.max) == INTEGER_CST))
-	    set_range_info (lhs, vr_result.type,
-			    wi::to_wide (vr_result.min),
-			    wi::to_wide (vr_result.max));
-	}
-      else if (POINTER_TYPE_P (TREE_TYPE (lhs))
-	       && ((vr_result.type == VR_RANGE
-		    && range_includes_zero_p (vr_result.min,
-					      vr_result.max) == 0)
-		   || (vr_result.type == VR_ANTI_RANGE
-		       && range_includes_zero_p (vr_result.min,
-						 vr_result.max) == 1)))
-	set_ptr_nonnull (lhs);
+      set_ssa_range_info (lhs, &vr_result);
     }
 }
 
@@ -224,21 +241,7 @@ evrp_range_analyzer::record_ranges_from_
 	  vr_values->update_value_range (output, &vr);
 
 	  /* Set the SSA with the value range.  */
-	  if (INTEGRAL_TYPE_P (TREE_TYPE (output)))
-	    {
-	      if ((vr.type == VR_RANGE || vr.type == VR_ANTI_RANGE)
-		  && (TREE_CODE (vr.min) == INTEGER_CST)
-		  && (TREE_CODE (vr.max) == INTEGER_CST))
-		set_range_info (output, vr.type,
-				wi::to_wide (vr.min),
-				wi::to_wide (vr.max));
-	    }
-	  else if (POINTER_TYPE_P (TREE_TYPE (output))
-		   && ((vr.type == VR_RANGE
-			&& range_includes_zero_p (vr.min, vr.max) == 0)
-		       || (vr.type == VR_ANTI_RANGE
-			   && range_includes_zero_p (vr.min, vr.max) == 1)))
-	    set_ptr_nonnull (output);
+	  set_ssa_range_info (output, &vr);
 	}
       else
 	vr_values->set_defs_to_varying (stmt);
Index: gcc/gimple-ssa-evrp-analyze.h
===================================================================
--- gcc/gimple-ssa-evrp-analyze.h	(revision 255163)
+++ gcc/gimple-ssa-evrp-analyze.h	(working copy)
@@ -68,6 +68,7 @@ class evrp_range_analyzer
   value_range *try_find_new_range (tree, tree op, tree_code code, tree limit);
   void record_ranges_from_incoming_edge (basic_block);
   void record_ranges_from_phis (basic_block);
+  void set_ssa_range_info (tree, value_range *);
 
   /* STACK holds the old VR.  */
   auto_vec<std::pair <tree, value_range*> > stack;
Index: gcc/testsuite/gcc.dg/pr80776-1.c
===================================================================
--- gcc/testsuite/gcc.dg/pr80776-1.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/pr80776-1.c	(working copy)
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wformat-overflow" } */
+
+extern __inline __attribute__ ((__always_inline__)) __attribute__ ((__gnu_inline__)) __attribute__ ((__artificial__)) int
+__attribute__ ((__nothrow__ , __leaf__)) sprintf (char *__restrict __s, const char *__restrict __fmt, ...)
+{
+  return __builtin___sprintf_chk (__s, 2 - 1,
+				  __builtin_object_size (__s, 2 > 1), __fmt, __builtin_va_arg_pack ());
+}
+char number[sizeof "999999"];
+int somerandom (void);
+void
+Foo (void)
+{
+  int i = somerandom ();
+  if (! (0 <= i))
+    __builtin_unreachable ();
+  if (! (0 <= i && i <= 999999))
+    __builtin_unreachable ();
+  sprintf (number, "%d", i); /* { dg-bogus "writing" } */
+}
Index: gcc/testsuite/gcc.dg/pr80776-2.c
===================================================================
--- gcc/testsuite/gcc.dg/pr80776-2.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/pr80776-2.c	(working copy)
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wformat-overflow" } */
+
+extern int sprintf (char *restrict, const char *restrict, ...)
+     __attribute__ ((__nothrow__));
+     extern int foo (void);
+
+int
+Fgenerate_new_buffer_name (void)
+{
+  char number[2];
+  int i = foo ();
+  if (i < 0)
+    __builtin_unreachable ();
+  if (i >= 2)
+    __builtin_unreachable ();
+  return sprintf (number, "%d", i); /* { dg-bogus "writing" } */
+}