re PR sanitizer/81981 (-fsanitize=undefined makes a -Wmaybe-uninitialized warning disappear)

	PR sanitizer/81981
	* gimple-fold.c (gimple_fold_call): Optimize away useless UBSAN_PTR
	and UBSAN_BOUNDS internal calls.  Clean up IFN_UBSAN_OBJECT_SIZE
	handling.  Use replace_call_with_value with NULL instead of
	gsi_replace, unlink_stmt_vdef and release_defs.

	* gcc.dg/ubsan/pr81981.c: New test.

From-SVN: r251641

gcc/ChangeLog

 2017-09-04  Jakub Jelinek  <jakub@redhat.com>
 
+	PR sanitizer/81981
+	* gimple-fold.c (gimple_fold_call): Optimize away useless UBSAN_PTR
+	and UBSAN_BOUNDS internal calls.  Clean up IFN_UBSAN_OBJECT_SIZE
+	handling.  Use replace_call_with_value with NULL instead of
+	gsi_replace, unlink_stmt_vdef and release_defs.
+
 	* gdbhooks.py (OptMachineModePrinter.to_string): Use 8 spaces
 	instead of tab.
 

gcc/gimple-fold.c

@@ -3936,18 +3936,43 @@ gimple_fold_call (gimple_stmt_iterator *gsi, bool inplace)
 					gimple_call_arg (stmt, 2));
 	  break;
 	case IFN_UBSAN_OBJECT_SIZE:
-	  if (integer_all_onesp (gimple_call_arg (stmt, 2))
-	      || (TREE_CODE (gimple_call_arg (stmt, 1)) == INTEGER_CST
-		  && TREE_CODE (gimple_call_arg (stmt, 2)) == INTEGER_CST
-		  && tree_int_cst_le (gimple_call_arg (stmt, 1),
-				      gimple_call_arg (stmt, 2))))
+	  {
+	    tree offset = gimple_call_arg (stmt, 1);
+	    tree objsize = gimple_call_arg (stmt, 2);
+	    if (integer_all_onesp (objsize)
+		|| (TREE_CODE (offset) == INTEGER_CST
+		    && TREE_CODE (objsize) == INTEGER_CST
+		    && tree_int_cst_le (offset, objsize)))
+	      {
+		replace_call_with_value (gsi, NULL_TREE);
+		return true;
+	      }
+	  }
+	  break;
+	case IFN_UBSAN_PTR:
+	  if (integer_zerop (gimple_call_arg (stmt, 1)))
 	    {
-	      gsi_replace (gsi, gimple_build_nop (), false);
-	      unlink_stmt_vdef (stmt);
-	      release_defs (stmt);
+	      replace_call_with_value (gsi, NULL_TREE);
 	      return true;
 	    }
 	  break;
+	case IFN_UBSAN_BOUNDS:
+	  {
+	    tree index = gimple_call_arg (stmt, 1);
+	    tree bound = gimple_call_arg (stmt, 2);
+	    if (TREE_CODE (index) == INTEGER_CST
+		&& TREE_CODE (bound) == INTEGER_CST)
+	      {
+		index = fold_convert (TREE_TYPE (bound), index);
+		if (TREE_CODE (index) == INTEGER_CST
+		    && tree_int_cst_le (index, bound))
+		  {
+		    replace_call_with_value (gsi, NULL_TREE);
+		    return true;
+		  }
+	      }
+	  }
+	  break;
 	case IFN_GOACC_DIM_SIZE:
 	case IFN_GOACC_DIM_POS:
 	  result = fold_internal_goacc_dim (stmt);

gcc/testsuite/ChangeLog

 2017-09-04  Jakub Jelinek  <jakub@redhat.com>
 
+	PR sanitizer/81981
+	* gcc.dg/ubsan/pr81981.c: New test.
+
 	PR tree-optimization/70043
 	PR testsuite/82093
 	* gfortran.dg/vect/pr70043.f90 (fn1): Start loop from 1 instead of 0.

gcc/testsuite/gcc.dg/ubsan/pr81981.c

+/* PR sanitizer/81981 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wmaybe-uninitialized -fsanitize=undefined -ffat-lto-objects" } */
+
+int v;
+
+int
+foo (int i)
+{
+  int t[1], u[1];
+  int n = 0;
+
+  if (i)
+    {
+      t[n] = i;
+      u[0] = i;
+    }
+
+  v = u[0];		/* { dg-warning "may be used uninitialized in this function" } */
+  return t[0];		/* { dg-warning "may be used uninitialized in this function" } */
+}