From: Marek Polacek <polacek@redhat.com>
Date: Fri, 20 Jan 2017 12:02:50 +0000 (+0000)
Subject: re PR c/64279 (Warning missing for "(cond) ? A : A" / if(cond) expr1; else expr1... 
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=2ebd93e1d7f611a9aa06c67c7b9bd82495d6adc2;p=gcc.git

re PR c/64279 (Warning missing for "(cond) ? A : A" / if(cond) expr1; else expr1; // same expression in if and else branch)

	PR c/64279
	* c-common.h (do_warn_duplicated_branches_r): Declare.
	* c-gimplify.c (c_genericize): Walk the function tree calling
	do_warn_duplicated_branches_r.
	* c-warn.c (expr_from_macro_expansion_r): New.
	(do_warn_duplicated_branches): New.
	(do_warn_duplicated_branches_r): New.
	* c.opt (Wduplicated-branches): New option.

	* c-typeck.c (build_conditional_expr): Warn about duplicated branches.

	* call.c (build_conditional_expr_1): Warn about duplicated branches.
	* semantics.c (finish_expr_stmt): Build statement using the proper
	location.

	* doc/invoke.texi: Document -Wduplicated-branches.
	* fold-const.c (operand_equal_p): Handle MODIFY_EXPR, INIT_EXPR,
	COMPOUND_EXPR, PREDECREMENT_EXPR, PREINCREMENT_EXPR,
	POSTDECREMENT_EXPR, POSTINCREMENT_EXPR, CLEANUP_POINT_EXPR, EXPR_STMT,
	STATEMENT_LIST, and RETURN_EXPR.  For non-pure non-const functions
	return 0 only when not OEP_LEXICOGRAPHIC.
	(fold_build_cleanup_point_expr): Use the expression
	location when building CLEANUP_POINT_EXPR.
	* tree-core.h (enum operand_equal_flag): Add OEP_LEXICOGRAPHIC.
	* tree.c (add_expr): Handle error_mark_node.

	* c-c++-common/Wduplicated-branches-1.c: New test.
	* c-c++-common/Wduplicated-branches-10.c: New test.
	* c-c++-common/Wduplicated-branches-11.c: New test.
	* c-c++-common/Wduplicated-branches-12.c: New test.
	* c-c++-common/Wduplicated-branches-2.c: New test.
	* c-c++-common/Wduplicated-branches-3.c: New test.
	* c-c++-common/Wduplicated-branches-4.c: New test.
	* c-c++-common/Wduplicated-branches-5.c: New test.
	* c-c++-common/Wduplicated-branches-6.c: New test.
	* c-c++-common/Wduplicated-branches-7.c: New test.
	* c-c++-common/Wduplicated-branches-8.c: New test.
	* c-c++-common/Wduplicated-branches-9.c: New test.
	* c-c++-common/Wimplicit-fallthrough-7.c: Coalesce dg-warning.
	* g++.dg/cpp0x/lambda/lambda-switch.C: Move dg-warning.
	* g++.dg/ext/builtin-object-size3.C: Likewise.
	* g++.dg/gomp/loop-1.C: Likewise.
	* g++.dg/warn/Wduplicated-branches1.C: New test.
	* g++.dg/warn/Wduplicated-branches2.C: New test.

From-SVN: r244705
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index b5bb07590ea..38eeb5a21b9 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,17 @@
+2017-01-20  Marek Polacek  <polacek@redhat.com>
+
+	PR c/64279
+	* doc/invoke.texi: Document -Wduplicated-branches.
+	* fold-const.c (operand_equal_p): Handle MODIFY_EXPR, INIT_EXPR,
+	COMPOUND_EXPR, PREDECREMENT_EXPR, PREINCREMENT_EXPR,
+	POSTDECREMENT_EXPR, POSTINCREMENT_EXPR, CLEANUP_POINT_EXPR, EXPR_STMT,
+	STATEMENT_LIST, and RETURN_EXPR.  For non-pure non-const functions
+	return 0 only when not OEP_LEXICOGRAPHIC.
+	(fold_build_cleanup_point_expr): Use the expression
+	location when building CLEANUP_POINT_EXPR.
+	* tree-core.h (enum operand_equal_flag): Add OEP_LEXICOGRAPHIC.
+	* tree.c (add_expr): Handle error_mark_node.
+
 2017-01-20  Martin Liska  <mliska@suse.cz>
 
 	PR lto/69188
diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index 778f8b187f2..8d1a61ef851 100644
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,3 +1,14 @@
+2017-01-20  Marek Polacek  <polacek@redhat.com>
+
+	PR c/64279
+	* c-common.h (do_warn_duplicated_branches_r): Declare.
+	* c-gimplify.c (c_genericize): Walk the function tree calling
+	do_warn_duplicated_branches_r.
+	* c-warn.c (expr_from_macro_expansion_r): New.
+	(do_warn_duplicated_branches): New.
+	(do_warn_duplicated_branches_r): New.
+	* c.opt (Wduplicated-branches): New option.
+
 2017-01-17  David Malcolm  <dmalcolm@redhat.com>
 
 	PR c++/71497
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index b838869dc25..06918dbaf1f 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -1537,6 +1537,7 @@ extern void maybe_warn_bool_compare (location_t, enum tree_code, tree, tree);
 extern bool maybe_warn_shift_overflow (location_t, tree, tree);
 extern void warn_duplicated_cond_add_or_warn (location_t, tree, vec<tree> **);
 extern bool diagnose_mismatched_attributes (tree, tree);
+extern tree do_warn_duplicated_branches_r (tree *, int *, void *);
 
 /* In c-attribs.c.  */
 extern bool attribute_takes_identifier_p (const_tree);
diff --git a/gcc/c-family/c-gimplify.c b/gcc/c-family/c-gimplify.c
index c327ca7028f..57edb41af0f 100644
--- a/gcc/c-family/c-gimplify.c
+++ b/gcc/c-family/c-gimplify.c
@@ -125,6 +125,10 @@ c_genericize (tree fndecl)
 		 &pset);
     }
 
+  if (warn_duplicated_branches)
+    walk_tree_without_duplicates (&DECL_SAVED_TREE (fndecl),
+				  do_warn_duplicated_branches_r, NULL);
+
   /* Dump the C-specific tree IR.  */
   dump_orig = get_dump_info (TDI_original, &local_dump_flags);
   if (dump_orig)
diff --git a/gcc/c-family/c-warn.c b/gcc/c-family/c-warn.c
index 1dbf47e8cd1..3c9077c5e80 100644
--- a/gcc/c-family/c-warn.c
+++ b/gcc/c-family/c-warn.c
@@ -2217,3 +2217,73 @@ warn_for_restrict (unsigned param_pos, vec<tree, va_gc> *args)
 
   free (arg_positions);
 }
+
+/* Callback function to determine whether an expression TP or one of its
+   subexpressions comes from macro expansion.  Used to suppress bogus
+   warnings.  */
+
+static tree
+expr_from_macro_expansion_r (tree *tp, int *, void *)
+{
+  if (CAN_HAVE_LOCATION_P (*tp)
+      && from_macro_expansion_at (EXPR_LOCATION (*tp)))
+    return integer_zero_node;
+
+  return NULL_TREE;
+}
+
+/* Possibly warn when an if-else has identical branches.  */
+
+static void
+do_warn_duplicated_branches (tree expr)
+{
+  tree thenb = COND_EXPR_THEN (expr);
+  tree elseb = COND_EXPR_ELSE (expr);
+
+  /* Don't bother if there's no else branch.  */
+  if (elseb == NULL_TREE)
+    return;
+
+  /* And don't warn for empty statements.  */
+  if (TREE_CODE (thenb) == NOP_EXPR
+      && TREE_TYPE (thenb) == void_type_node
+      && TREE_OPERAND (thenb, 0) == size_zero_node)
+    return;
+
+  /* ... or empty branches.  */
+  if (TREE_CODE (thenb) == STATEMENT_LIST
+      && STATEMENT_LIST_HEAD (thenb) == NULL)
+    return;
+
+  /* Compute the hash of the then branch.  */
+  inchash::hash hstate0 (0);
+  inchash::add_expr (thenb, hstate0);
+  hashval_t h0 = hstate0.end ();
+
+  /* Compute the hash of the else branch.  */
+  inchash::hash hstate1 (0);
+  inchash::add_expr (elseb, hstate1);
+  hashval_t h1 = hstate1.end ();
+
+  /* Compare the hashes.  */
+  if (h0 == h1
+      && operand_equal_p (thenb, elseb, OEP_LEXICOGRAPHIC)
+      /* Don't warn if any of the branches or their subexpressions comes
+	 from a macro.  */
+      && !walk_tree_without_duplicates (&thenb, expr_from_macro_expansion_r,
+					NULL)
+      && !walk_tree_without_duplicates (&elseb, expr_from_macro_expansion_r,
+					NULL))
+    warning_at (EXPR_LOCATION (expr), OPT_Wduplicated_branches,
+		"this condition has identical branches");
+}
+
+/* Callback for c_genericize to implement -Wduplicated-branches.  */
+
+tree
+do_warn_duplicated_branches_r (tree *tp, int *, void *)
+{
+  if (TREE_CODE (*tp) == COND_EXPR)
+    do_warn_duplicated_branches (*tp);
+  return NULL_TREE;
+}
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 3bb42f6d913..a1b3ae5c0b0 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -468,6 +468,10 @@ Wdiv-by-zero
 C ObjC C++ ObjC++ Var(warn_div_by_zero) Init(1) Warning
 Warn about compile-time integer division by zero.
 
+Wduplicated-branches
+C ObjC C++ ObjC++ Var(warn_duplicated_branches) Init(0) Warning
+Warn about duplicated branches in if-else statements.
+
 Wduplicated-cond
 C ObjC C++ ObjC++ Var(warn_duplicated_cond) Init(0) Warning
 Warn about duplicated conditions in an if-else-if chain.
diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog
index 5b590b33b8b..18ef3c2e37e 100644
--- a/gcc/c/ChangeLog
+++ b/gcc/c/ChangeLog
@@ -1,3 +1,8 @@
+2017-01-20  Marek Polacek  <polacek@redhat.com>
+
+	PR c/64279
+	* c-typeck.c (build_conditional_expr): Warn about duplicated branches.
+
 2017-01-13  Richard Biener  <rguenther@suse.de>
 
 	* gimple-parser.c (c_parser_gimple_compound_statement): Handle
diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 96e7351bf45..ed8ffe4c2e7 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -5193,6 +5193,15 @@ build_conditional_expr (location_t colon_loc, tree ifexp, bool ifexp_bcp,
     ret = build1 (EXCESS_PRECISION_EXPR, semantic_result_type, ret);
 
   protected_set_expr_location (ret, colon_loc);
+
+  /* If the OP1 and OP2 are the same and don't have side-effects,
+     warn here, because the COND_EXPR will be turned into OP1.  */
+  if (warn_duplicated_branches
+      && TREE_CODE (ret) == COND_EXPR
+      && (op1 == op2 || operand_equal_p (op1, op2, 0)))
+    warning_at (EXPR_LOCATION (ret), OPT_Wduplicated_branches,
+		"this condition has identical branches");
+
   return ret;
 }
 
diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index bfd898d874b..6554cb7cc75 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,10 @@
+2017-01-20  Marek Polacek  <polacek@redhat.com>
+
+	PR c/64279
+	* call.c (build_conditional_expr_1): Warn about duplicated branches.
+	* semantics.c (finish_expr_stmt): Build statement using the proper
+	location.
+
 2017-01-19  Jason Merrill  <jason@redhat.com>
 
 	US 20 - forwarding references and class template argument deduction
diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 0059a395ae4..a78e1a9c8a2 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -5302,6 +5302,13 @@ build_conditional_expr_1 (location_t loc, tree arg1, tree arg2, tree arg3,
  valid_operands:
   result = build3_loc (loc, COND_EXPR, result_type, arg1, arg2, arg3);
 
+  /* If the ARG2 and ARG3 are the same and don't have side-effects,
+     warn here, because the COND_EXPR will be turned into ARG2.  */
+  if (warn_duplicated_branches
+      && (arg2 == arg3 || operand_equal_p (arg2, arg3, 0)))
+    warning_at (EXPR_LOCATION (result), OPT_Wduplicated_branches,
+		"this condition has identical branches");
+
   /* We can't use result_type below, as fold might have returned a
      throw_expr.  */
 
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 42024755e4f..55710e64c97 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -670,6 +670,7 @@ tree
 finish_expr_stmt (tree expr)
 {
   tree r = NULL_TREE;
+  location_t loc = EXPR_LOCATION (expr);
 
   if (expr != NULL_TREE)
     {
@@ -694,7 +695,7 @@ finish_expr_stmt (tree expr)
       if (TREE_CODE (expr) != CLEANUP_POINT_EXPR)
 	{
 	  if (TREE_CODE (expr) != EXPR_STMT)
-	    expr = build_stmt (input_location, EXPR_STMT, expr);
+	    expr = build_stmt (loc, EXPR_STMT, expr);
 	  expr = maybe_cleanup_point_expr_void (expr);
 	}
 
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index a7b494b76e2..5b96f362c1a 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -3734,7 +3734,7 @@ Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
 -Warray-bounds=1 @r{(only with} @option{-O2}@r{)}  @gol
 -Wbool-compare  @gol
 -Wbool-operation  @gol
--Wc++11-compat  -Wc++14-compat@gol
+-Wc++11-compat  -Wc++14-compat  @gol
 -Wchar-subscripts  @gol
 -Wcomment  @gol
 -Wduplicate-decl-specifier @r{(C and Objective-C only)} @gol
@@ -5263,6 +5263,22 @@ Incrementing a boolean is invalid in C++1z, and deprecated otherwise.)
 
 This warning is enabled by @option{-Wall}.
 
+@item -Wduplicated-branches
+@opindex Wno-duplicated-branches
+@opindex Wduplicated-branches
+Warn when an if-else has identical branches.  This warning detects cases like
+@smallexample
+if (p != NULL)
+  return 0;
+else
+  return 0;
+@end smallexample
+It doesn't warn when both branches contain just a null statement.  This warning
+also warn for conditional operators:
+@smallexample
+  int i = x ? *p : *p;
+@end smallexample
+
 @item -Wduplicated-cond
 @opindex Wno-duplicated-cond
 @opindex Wduplicated-cond
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index cfd270ce83c..5576d592988 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -2722,6 +2722,9 @@ combine_comparisons (location_t loc,
    If OEP_ADDRESS_OF is set, we are actually comparing addresses of objects,
    not values of expressions.
 
+   If OEP_LEXICOGRAPHIC is set, then also handle expressions with side-effects
+   such as MODIFY_EXPR, RETURN_EXPR, as well as STATEMENT_LISTs.
+
    Unless OEP_MATCH_SIDE_EFFECTS is set, the function returns false on
    any operand with side effect.  This is unnecesarily conservative in the
    case we know that arg0 and arg1 are in disjoint code paths (such as in
@@ -3154,6 +3157,23 @@ operand_equal_p (const_tree arg0, const_tree arg1, unsigned int flags)
 	case BIT_INSERT_EXPR:
 	  return OP_SAME (0) && OP_SAME (1) && OP_SAME (2);
 
+	case MODIFY_EXPR:
+	case INIT_EXPR:
+	case COMPOUND_EXPR:
+	case PREDECREMENT_EXPR:
+	case PREINCREMENT_EXPR:
+	case POSTDECREMENT_EXPR:
+	case POSTINCREMENT_EXPR:
+	  if (flags & OEP_LEXICOGRAPHIC)
+	    return OP_SAME (0) && OP_SAME (1);
+	  return 0;
+
+	case CLEANUP_POINT_EXPR:
+	case EXPR_STMT:
+	  if (flags & OEP_LEXICOGRAPHIC)
+	    return OP_SAME (0);
+	  return 0;
+
 	default:
 	  return 0;
 	}
@@ -3190,7 +3210,7 @@ operand_equal_p (const_tree arg0, const_tree arg1, unsigned int flags)
 	      cef &= ECF_CONST | ECF_PURE;
 	    else
 	      cef &= ECF_CONST;
-	    if (!cef)
+	    if (!cef && !(flags & OEP_LEXICOGRAPHIC))
 	      return 0;
 	  }
 
@@ -3269,8 +3289,39 @@ operand_equal_p (const_tree arg0, const_tree arg1, unsigned int flags)
 	    }
 	  return 1;
 	}
+      else if (TREE_CODE (arg0) == STATEMENT_LIST
+	       && (flags & OEP_LEXICOGRAPHIC))
+	{
+	  /* Compare the STATEMENT_LISTs.  */
+	  tree_stmt_iterator tsi1, tsi2;
+	  tree body1 = CONST_CAST_TREE (arg0);
+	  tree body2 = CONST_CAST_TREE (arg1);
+	  for (tsi1 = tsi_start (body1), tsi2 = tsi_start (body2); ;
+	       tsi_next (&tsi1), tsi_next (&tsi2))
+	    {
+	      /* The lists don't have the same number of statements.  */
+	      if (tsi_end_p (tsi1) ^ tsi_end_p (tsi2))
+		return 0;
+	      if (tsi_end_p (tsi1) && tsi_end_p (tsi2))
+		return 1;
+	      if (!operand_equal_p (tsi_stmt (tsi1), tsi_stmt (tsi2),
+				    OEP_LEXICOGRAPHIC))
+		return 0;
+	    }
+	}
       return 0;
 
+    case tcc_statement:
+      switch (TREE_CODE (arg0))
+	{
+	case RETURN_EXPR:
+	  if (flags & OEP_LEXICOGRAPHIC)
+	    return OP_SAME_WITH_NULL (0);
+	  return 0;
+	default:
+	  return 0;
+	 }
+
     default:
       return 0;
     }
@@ -13897,7 +13948,7 @@ fold_build_cleanup_point_expr (tree type, tree expr)
         return expr;
     }
 
-  return build1 (CLEANUP_POINT_EXPR, type, expr);
+  return build1_loc (EXPR_LOCATION (expr), CLEANUP_POINT_EXPR, type, expr);
 }
 
 /* Given a pointer value OP0 and a type TYPE, return a simplified version
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 14ca4e90064..201395d9e55 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,25 @@
+2017-01-20  Marek Polacek  <polacek@redhat.com>
+
+	PR c/64279
+	* c-c++-common/Wduplicated-branches-1.c: New test.
+	* c-c++-common/Wduplicated-branches-10.c: New test.
+	* c-c++-common/Wduplicated-branches-11.c: New test.
+	* c-c++-common/Wduplicated-branches-12.c: New test.
+	* c-c++-common/Wduplicated-branches-2.c: New test.
+	* c-c++-common/Wduplicated-branches-3.c: New test.
+	* c-c++-common/Wduplicated-branches-4.c: New test.
+	* c-c++-common/Wduplicated-branches-5.c: New test.
+	* c-c++-common/Wduplicated-branches-6.c: New test.
+	* c-c++-common/Wduplicated-branches-7.c: New test.
+	* c-c++-common/Wduplicated-branches-8.c: New test.
+	* c-c++-common/Wduplicated-branches-9.c: New test.
+	* c-c++-common/Wimplicit-fallthrough-7.c: Coalesce dg-warning.
+	* g++.dg/cpp0x/lambda/lambda-switch.C: Move dg-warning.
+	* g++.dg/ext/builtin-object-size3.C: Likewise.
+	* g++.dg/gomp/loop-1.C: Likewise.
+	* g++.dg/warn/Wduplicated-branches1.C: New test.
+	* g++.dg/warn/Wduplicated-branches2.C: New test.
+
 2017-01-20  Martin Liska  <mliska@suse.cz>
 
 	PR lto/69188
diff --git a/gcc/testsuite/c-c++-common/Wduplicated-branches-1.c b/gcc/testsuite/c-c++-common/Wduplicated-branches-1.c
new file mode 100644
index 00000000000..c0b93fcf97a
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wduplicated-branches-1.c
@@ -0,0 +1,187 @@
+/* PR c/64279 */
+/* { dg-do compile } */
+/* { dg-options "-Wduplicated-branches -O2" } */
+
+extern void foo (int);
+extern int g;
+extern int a[10];
+
+int
+f (int i, int *p)
+{
+  const int j = 0;
+  if (j == 0)
+    {
+      if (i > 10) /* { dg-warning "this condition has identical branches" } */
+	/* Optimizers can figure out that this is 1.  */
+	*p = j * 2 + 1;
+      else
+	*p = 1;
+    }
+
+  if (i)
+    ;
+  else
+    ;
+
+  if (i == 0) /* { dg-warning "this condition has identical branches" } */
+    return 0;
+  else
+    return 0;
+
+  if (i == 1) /* { dg-warning "this condition has identical branches" } */
+    {
+      g = 10;
+    }
+  else
+    {
+      g = 10;
+    }
+
+  const char *s;
+  if (i == 2) /* { dg-warning "this condition has identical branches" } */
+    s = "foo";
+  else
+    s = "foo";
+
+  if (i == 3) /* { dg-warning "this condition has identical branches" } */
+    g = a[i];
+  else
+    g = a[i];
+
+  if (i == 4) /* { dg-warning "this condition has identical branches" } */
+    return i ? 1 : g;
+  else
+    return i ? 1 : g;
+
+  if (i == 5) /* { dg-warning "this condition has identical branches" } */
+    {
+      {
+	{
+	  {
+	    g++;
+	  }
+	}
+      }
+    }
+  else
+    {
+      {
+	{
+	  {
+	    g++;
+	  }
+	}
+      }
+    }
+
+  if (i == 6) /* { dg-warning "this condition has identical branches" } */
+    g = i * 6;
+  else
+    g = i * 6;
+
+  /* Don't warn.  */
+  if (i == 7)
+    g = i / 6;
+  else
+    g = 6 / i;
+
+  if (i == 8) /* { dg-warning "this condition has identical branches" } */
+    return i * 8 * i * 8;
+  else
+    return 8 * i * 8 * i;
+
+
+  if (i == 9) /* { dg-warning "this condition has identical branches" } */
+    {
+      p++;
+      return *p;
+    }
+  else
+    {
+      p++;
+      return *p;
+    }
+
+  /* Don't warn.  */
+  if (i == 10)
+    return *++p;
+  else
+    return ++*p;
+
+  if (i == 11) /* { dg-warning "this condition has identical branches" } */
+    {
+      foo (6);
+    }
+  else
+    {
+      foo (6);
+    }
+
+  if (i == 12) /* { dg-warning "this condition has identical branches" } */
+    {
+      foo (6 + i), foo (2);
+    }
+  else
+    {
+      foo (6 + i), foo (2);
+    }
+
+  if (i == 13) /* { dg-warning "this condition has identical branches" } */
+    p += (g + 1);
+  else
+    p += (g + 1);
+
+  if (i == 14) /* { dg-warning "this condition has identical branches" } */
+    {
+      foo (7);
+      *p = 0;
+      foo (9);
+    }
+  else
+    {
+      foo (7);
+      *p = 0;
+      foo (9);
+    }
+
+  if (i == 15) /* { dg-warning "this condition has identical branches" } */
+    p += (g + (1 + 2));
+  else
+    p += (g + (1 + 1 + 1));
+
+  if (i == 16) /* { dg-warning "this condition has identical branches" } */
+    foo (10 + g);
+  else
+    foo (g + 10);
+
+  if (i == 17) /* { dg-warning "this condition has identical branches" } */
+    ({ foo (i); });
+  else
+    ({ foo (i); });
+
+  if (i == 18)
+    {
+      if (i == 19)
+	{
+	  if (i == 20) /* { dg-warning "this condition has identical branches" } */
+	    foo (++i);
+	  else
+	    foo (++i);
+	}
+    }
+
+  /* Don't warn.  */
+  if (i == 21)
+    {
+      foo (1);
+      foo (2);
+    }
+  else
+    {
+      foo (2);
+      foo (1);
+    }
+
+  return 0;
+}
diff --git a/gcc/testsuite/c-c++-common/Wduplicated-branches-10.c b/gcc/testsuite/c-c++-common/Wduplicated-branches-10.c
new file mode 100644
index 00000000000..8d918efcdc3
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wduplicated-branches-10.c
@@ -0,0 +1,18 @@
+/* PR c/64279 */
+/* { dg-do compile } */
+/* { dg-options "-Wduplicated-branches" } */
+
+#define DEBUG(msg) ;
+
+void
+f (int i)
+{
+  if (i > 9)
+    {
+      DEBUG ("foo");
+    }
+  else
+    {
+      DEBUG ("bar");
+    }
+}
diff --git a/gcc/testsuite/c-c++-common/Wduplicated-branches-11.c b/gcc/testsuite/c-c++-common/Wduplicated-branches-11.c
new file mode 100644
index 00000000000..70d86cf7f05
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wduplicated-branches-11.c
@@ -0,0 +1,75 @@
+/* PR c/64279 */
+/* { dg-do compile } */
+/* { dg-options "-Wduplicated-branches" } */
+
+int
+f (int p)
+{
+  if (p == 0)
+    {
+      p += 1, ++p;
+    }
+  else
+    {
+      p -= 1, ++p;
+    }
+
+  if (p == 1)
+    {
+    }
+  else
+    p++;
+
+  if (p == 2)
+    p++;
+  else
+    {
+    }
+
+  if (p == 3)
+    {
+    }
+  else
+    {
+    }
+
+  if (p == 4)
+    {
+      ++p;
+      return p;
+    }
+  else
+    {
+      p++;
+      return p;
+    }
+
+  if (p == 5)
+    ++p;
+  else
+    p++;
+
+  if (p == 6)
+    {
+      ++p;
+      ++p;
+      return p;
+    }
+  else
+    {
+      ++p;
+      return p;
+    }
+
+  if (p == 7)
+    {
+      ++p;
+      return p;
+    }
+  else
+    {
+      ++p;
+      ++p;
+      return p;
+    }
+}
diff --git a/gcc/testsuite/c-c++-common/Wduplicated-branches-12.c b/gcc/testsuite/c-c++-common/Wduplicated-branches-12.c
new file mode 100644
index 00000000000..cd746f1ad30
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wduplicated-branches-12.c
@@ -0,0 +1,16 @@
+/* PR c/64279 */
+/* { dg-do compile } */
+/* { dg-options "-Wduplicated-branches" } */
+
+void
+f (int i)
+{
+  if (i) /* { dg-warning "this condition has identical branches" } */
+    return 0;
+/* { dg-warning ".return. with a value" "" { target c } .-1 } */
+/* { dg-error "return-statement with a value" "" { target c++ } .-2 } */
+  else
+   return 0;
+/* { dg-warning ".return. with a value" "" { target c } .-1 } */
+/* { dg-error "return-statement with a value" "" { target c++ } .-2 } */
+}
diff --git a/gcc/testsuite/c-c++-common/Wduplicated-branches-2.c b/gcc/testsuite/c-c++-common/Wduplicated-branches-2.c
new file mode 100644
index 00000000000..8669dd6a629
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wduplicated-branches-2.c
@@ -0,0 +1,114 @@
+/* PR c/64279 */
+/* { dg-do compile } */
+/* { dg-options "-Wduplicated-branches -O2" } */
+
+void
+f (int *p)
+{
+  if (*p > 0)
+    {
+      if (x == 0) /* { dg-error "undeclared|not declared" } */
+	*p = 5;
+      else
+	*p = 6;
+    }
+}
+
+void
+f2 (int *p)
+{
+  if (*p > 0)
+    {
+      if (*p > 2)
+	*p = x; /* { dg-error "undeclared|not declared" } */
+      else
+	*p = 6;
+    }
+}
+
+void
+f3 (int *p)
+{
+  if (*p > 0)
+    {
+      if (*p > 2)
+	*p = 8;
+      else
+	*p = x; /* { dg-error "undeclared|not declared" } */
+    }
+}
+
+void
+f4 (int *p)
+{
+  if (*p > 0)
+    {
+      if (x == 0) /* { dg-error "undeclared|not declared" } */
+	*p = 5;
+      else
+	*p = 6;
+    }
+  else
+    {
+      if (x == 0) /* { dg-error "not declared" "" { target c++ } } */
+	*p = 7;
+      else
+	*p = 6;
+    }
+}
+
+void
+f5 (int *p)
+{
+  if (*p > 0)
+    {
+      if (*p > 2)
+	*p = x; /* { dg-error "undeclared|not declared" } */
+      else
+	*p = 6;
+    }
+  else
+    {
+      if (x == 0) /* { dg-error "not declared" "" { target c++ } } */
+	*p = 5;
+      else
+	*p = 6;
+    }
+}
+
+void
+f6 (int *p)
+{
+  if (*p > 0)
+    {
+      if (*p > 2)
+	*p = 8;
+      else
+	*p = x; /* { dg-error "undeclared|not declared" } */
+    }
+  else
+    {
+      if (x == 0) /* { dg-error "not declared" "" { target c++ } } */
+	*p = 5;
+      else
+	*p = 6;
+    }
+}
+
+void
+f7 (int i)
+{
+  if (i > 5)
+    ({ x++; }); /* { dg-error "undeclared|not declared" } */
+  else
+    ({ i++; });
+}
+
+void
+f8 (int i)
+{
+  if (i > 5)
+    ({ i++; });
+  else
+    ({ x++; }); /* { dg-error "undeclared|not declared" } */
+}
diff --git a/gcc/testsuite/c-c++-common/Wduplicated-branches-3.c b/gcc/testsuite/c-c++-common/Wduplicated-branches-3.c
new file mode 100644
index 00000000000..e1883843d54
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wduplicated-branches-3.c
@@ -0,0 +1,19 @@
+/* PR c/64279 */
+/* { dg-do compile } */
+/* { dg-options "-Wduplicated-branches" } */
+
+extern int *g;
+
+void
+f (short int i)
+{
+  if (i == 0) /* { dg-warning "this condition has identical branches" } */
+    *g = (int) i;
+  else
+    *g = (int) i;
+
+  if (i == 1)
+    *g = (unsigned char) i;
+  else
+    *g = (signed char) i;
+}
diff --git a/gcc/testsuite/c-c++-common/Wduplicated-branches-4.c b/gcc/testsuite/c-c++-common/Wduplicated-branches-4.c
new file mode 100644
index 00000000000..79af5493866
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wduplicated-branches-4.c
@@ -0,0 +1,35 @@
+/* PR c/64279 */
+/* { dg-do compile } */
+/* { dg-options "-Wduplicated-branches" } */
+
+extern int *g;
+extern const int *q;
+
+void
+f (int i)
+{
+  int j;
+
+  if (i == 0)
+    for (j = 0; j < 10; j++)
+       ++*g;
+  else
+    for (j = 0; j < 10; j++)
+       ++*g;
+
+  if (i == 1)
+    {
+      int i = 10;
+      *g = i;
+    }
+  else
+    {
+      int i = 10;
+      *g = i;
+    }
+
+  if (i == 3)
+    q = (const int []){1};
+  else
+    q = (const int []){1};
+}
diff --git a/gcc/testsuite/c-c++-common/Wduplicated-branches-5.c b/gcc/testsuite/c-c++-common/Wduplicated-branches-5.c
new file mode 100644
index 00000000000..f2eb8ecfefa
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wduplicated-branches-5.c
@@ -0,0 +1,24 @@
+/* PR c/64279 */
+/* { dg-do compile } */
+/* { dg-options "-Wduplicated-branches" } */
+
+extern int g;
+extern void foo ();
+#define A g = i
+#define B g = i
+#define DOIT() foo()
+#define DOIT2() foo()
+
+void
+f (int i)
+{
+  if (i == 0)
+    A;
+  else
+    B;
+
+  if (i == 1)
+    DOIT();
+  else
+    DOIT2();
+}
diff --git a/gcc/testsuite/c-c++-common/Wduplicated-branches-6.c b/gcc/testsuite/c-c++-common/Wduplicated-branches-6.c
new file mode 100644
index 00000000000..0010693d81a
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wduplicated-branches-6.c
@@ -0,0 +1,12 @@
+/* PR c/64279 */
+/* { dg-do compile } */
+/* { dg-options "-Wduplicated-branches" } */
+
+void
+f (int i)
+{
+  if (i == 0)
+    ;
+  else if (i == 1)
+    ;
+}
diff --git a/gcc/testsuite/c-c++-common/Wduplicated-branches-7.c b/gcc/testsuite/c-c++-common/Wduplicated-branches-7.c
new file mode 100644
index 00000000000..03721dc4cb6
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wduplicated-branches-7.c
@@ -0,0 +1,36 @@
+/* PR c/64279 */
+/* { dg-do compile } */
+/* { dg-options "-Wduplicated-branches" } */
+
+struct S
+{
+  int x;
+} s;
+int a[10];
+
+#define XMEM(R) ((R).x)
+#define XSTR(R) ((R).x)
+
+void
+f (int i)
+{
+  if (i)
+    XMEM(s) = 1;
+  else
+    XSTR(s) = 1;
+
+  if (i) /* { dg-warning "this condition has identical branches" } */
+    s.x = 1;
+  else
+    s.x = 1;
+
+  if (i)
+    XMEM(s) = 1;
+  else
+    s.x = 1;
+
+  if (i)
+    s.x = 1;
+  else
+    XMEM(s) = 1;
+}
diff --git a/gcc/testsuite/c-c++-common/Wduplicated-branches-8.c b/gcc/testsuite/c-c++-common/Wduplicated-branches-8.c
new file mode 100644
index 00000000000..c5e8ca07489
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wduplicated-branches-8.c
@@ -0,0 +1,73 @@
+/* PR c/64279 */
+/* { dg-do compile } */
+/* { dg-options "-Wduplicated-branches" } */
+
+#define A 5
+#define B 5
+#define I i
+extern int a[10];
+extern int g;
+
+int
+f (int i)
+{
+  if (i == 1) /* { dg-warning "this condition has identical branches" } */
+   return a[5];
+  else
+   return a[5];
+
+  if (i == 2) /* { dg-bogus "this condition has identical branches" "" { xfail *-*-* } } */
+   return a[A];
+  else
+   return a[5];
+
+  if (i == 3) /* { dg-bogus "this condition has identical branches" "" { xfail *-*-* } } */
+   return a[5];
+  else
+   return a[A];
+
+  if (i == 4) /* { dg-warning "this condition has identical branches" } */
+   return a[A];
+  else
+   return a[A];
+
+  if (i == 5) /* { dg-warning "this condition has identical branches" } */
+   return a[i];
+  else
+   return a[i];
+
+  if (i == 6) /* { dg-bogus "this condition has identical branches" "" { xfail *-*-* } } */
+   return a[I];
+  else
+   return a[i];
+
+  if (i == 7) /* { dg-bogus "this condition has identical branches" "" { xfail *-*-* } } */
+   return a[i];
+  else
+   return a[I];
+
+  if (i == 8) /* { dg-warning "this condition has identical branches" } */
+   return a[I];
+  else
+   return a[I];
+
+  if (i == 10) /* { dg-bogus "this condition has identical branches" "" { xfail *-*-* } } */
+    g += A;
+  else
+    g += B;
+
+  if (i == 11) /* { dg-bogus "this condition has identical branches" "" { xfail *-*-* } } */
+    g += B;
+  else
+    g += A;
+
+  if (i == 12) /* { dg-bogus "this condition has identical branches" "" { xfail *-*-* } } */
+    g += A;
+  else
+    g += 5;
+
+  if (i == 12) /* { dg-bogus "this condition has identical branches" "" { xfail *-*-* } } */
+    g += 5;
+  else
+    g += A;
+}
diff --git a/gcc/testsuite/c-c++-common/Wduplicated-branches-9.c b/gcc/testsuite/c-c++-common/Wduplicated-branches-9.c
new file mode 100644
index 00000000000..9b21776af2e
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wduplicated-branches-9.c
@@ -0,0 +1,46 @@
+/* PR c/64279 */
+/* { dg-do compile } */
+/* { dg-options "-Wduplicated-branches" } */
+
+extern int *p, foo (void), a[10];
+#define N 5
+#define M 5
+#define I i
+
+void
+f (int i)
+{
+  *p += i ? 1 : 1; /* { dg-warning "this condition has identical branches" } */
+  *p += i ? N : M; /* { dg-bogus "this condition has identical branches" "" { xfail *-*-* } } */
+  *p += i ? M : N; /* { dg-bogus "this condition has identical branches" "" { xfail *-*-* } } */
+  *p += i ? i : i; /* { dg-warning "this condition has identical branches" } */
+  *p += i ? i++ : i++; /* { dg-warning "this condition has identical branches" } */
+  *p += i ? foo () : foo (); /* { dg-warning "this condition has identical branches" } */
+  *p += i ? ({ i++; }) : ({ i++; }); /* { dg-warning "this condition has identical branches" } */
+  *p += i ? a[i] : a[i]; /* { dg-warning "this condition has identical branches" } */
+  *p += i ? a[5] : a[5]; /* { dg-warning "this condition has identical branches" } */
+  *p += i ? a[N] : a[M]; /* { dg-bogus "this condition has identical branches" "" { xfail *-*-* } } */
+  *p += i ? a[5] : a[M]; /* { dg-bogus "this condition has identical branches" "" { xfail *-*-* } } */
+  *p += i ? a[M] : a[5]; /* { dg-bogus "this condition has identical branches" "" { xfail *-*-* } } */
+  *p += i ? a[I] : a[I]; /* { dg-warning "this condition has identical branches" } */
+  *p += i ? a[i] : a[I]; /* { dg-bogus "this condition has identical branches" "" { xfail *-*-* } } */
+  *p += i ? a[I] : a[i]; /* { dg-bogus "this condition has identical branches" "" { xfail *-*-* } } */
+
+  *p += i ?: 1;
+  *p += i ?: M;
+  *p += i ?: N;
+  *p += i ?: i; /* { dg-warning "this condition has identical branches" "" { target c++ } } */
+  *p += i ?: i++;
+  *p += i ?: foo ();
+  *p += i ?: ({ i++; });
+  *p += i ?: a[i];
+  *p += i ?: a[5];
+  *p += i ?: a[M];
+  *p += i ?: a[M];
+  *p += i ?: a[5];
+  *p += i ?: a[I];
+  *p += i ?: a[I];
+  *p += i ?: a[i];
+
+  *p += (i > 5 ? (i > 10 ? i : i) : i); /* { dg-warning "this condition has identical branches" } */
+}
diff --git a/gcc/testsuite/c-c++-common/Wimplicit-fallthrough-7.c b/gcc/testsuite/c-c++-common/Wimplicit-fallthrough-7.c
index 21a158ca14f..898e5fa6d46 100644
--- a/gcc/testsuite/c-c++-common/Wimplicit-fallthrough-7.c
+++ b/gcc/testsuite/c-c++-common/Wimplicit-fallthrough-7.c
@@ -39,9 +39,9 @@ f (int i)
   switch (i)
     {
     case 1:
-      do /* { dg-warning "statement may fall through" "" { target c++ } 42 } */
+      do
 	bar (2);
-      while (--i); /* { dg-warning "statement may fall through" "" { target c } 44 } */
+      while (--i); /* { dg-warning "statement may fall through" } */
     case 2:
       bar (99);
     }
diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-switch.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-switch.C
index d71d3ade2ac..ee87defac9f 100644
--- a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-switch.C
+++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-switch.C
@@ -16,11 +16,11 @@ main ()
 	      break;		// { dg-error "break" }
 	    }
 	  };
-	  l = []()
+	  l = []()		// { dg-warning "statement will never be executed" }
 	    {
 	    case 3:		// { dg-error "case" }
 	      break;		// { dg-error "break" }
-	    };			// { dg-warning "statement will never be executed" }
+	    };
 	}
     }
 }
diff --git a/gcc/testsuite/g++.dg/ext/builtin-object-size3.C b/gcc/testsuite/g++.dg/ext/builtin-object-size3.C
index 0207f9ab667..b2a9170fc30 100644
--- a/gcc/testsuite/g++.dg/ext/builtin-object-size3.C
+++ b/gcc/testsuite/g++.dg/ext/builtin-object-size3.C
@@ -3,7 +3,7 @@
 
 void baz (int *, int *);
 
-#define MEMCPY(d,s,l) __builtin___memcpy_chk (d, s, l, __builtin_object_size (d, 0))
+#define MEMCPY(d,s,l) __builtin___memcpy_chk (d, s, l, __builtin_object_size (d, 0)) // { dg-warning "writing" }
 
 int
 foo ()
@@ -20,7 +20,7 @@ bar ()
 {
   int *p = new int;
   int *q = new int[4];
-  MEMCPY (p, "abcdefghijklmnopqrstuvwxyz", sizeof (int) + 1);		// { dg-warning "writing" }
-  MEMCPY (q, "abcdefghijklmnopqrstuvwxyz", 4 * sizeof (int) + 1);	// { dg-warning "writing" }
+  MEMCPY (p, "abcdefghijklmnopqrstuvwxyz", sizeof (int) + 1); // { dg-message "in expansion of macro" }
+  MEMCPY (q, "abcdefghijklmnopqrstuvwxyz", 4 * sizeof (int) + 1); // { dg-message "in expansion of macro" }
   baz (p, q);
 }
diff --git a/gcc/testsuite/g++.dg/gomp/loop-1.C b/gcc/testsuite/g++.dg/gomp/loop-1.C
index de08eb3271d..b3db0f4736b 100644
--- a/gcc/testsuite/g++.dg/gomp/loop-1.C
+++ b/gcc/testsuite/g++.dg/gomp/loop-1.C
@@ -82,8 +82,8 @@ f1 (int x)
     for (j = i + 3; j < 16; j += 2) /* { dg-error "initializer expression refers to iteration variable" } */
       ;
   #pragma omp for collapse(2)
-  for (i = 0; i < 16; i++) /* { dg-error "initializer expression refers to iteration variable" } */
-    for (j = baz (&i); j < 16; j += 2)
+  for (i = 0; i < 16; i++)
+    for (j = baz (&i); j < 16; j += 2) /* { dg-error "initializer expression refers to iteration variable" } */
       ;
   #pragma omp for collapse(2)
   for (i = 0; i < 16; i++)
@@ -215,8 +215,8 @@ f2 (int x)
     for (int j = i + 3; j < 16; j += 2) /* { dg-error "initializer expression refers to iteration variable" } */
       ;
   #pragma omp for collapse(2)
-  for (int i = 0; i < 16; i++) /* { dg-error "initializer expression refers to iteration variable" } */
-    for (int j = baz (&i); j < 16; j += 2)
+  for (int i = 0; i < 16; i++)
+    for (int j = baz (&i); j < 16; j += 2) /* { dg-error "initializer expression refers to iteration variable" } */
       ;
   #pragma omp for collapse(2)
   for (int i = 0; i < 16; i++)
diff --git a/gcc/testsuite/g++.dg/warn/Wduplicated-branches1.C b/gcc/testsuite/g++.dg/warn/Wduplicated-branches1.C
new file mode 100644
index 00000000000..7ebd55e190f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wduplicated-branches1.C
@@ -0,0 +1,21 @@
+// PR c/64279
+// { dg-do compile }
+// { dg-options "-Wduplicated-branches" }
+
+template <typename T>
+void
+f (char i, int *p)
+{
+  if (i)
+    *p = (signed short) i;
+  else
+    *p = (unsigned short) i;
+
+  if (i) // { dg-warning "this condition has identical branches" }
+    *p = (T) i;
+  else
+    *p = (unsigned short) i;
+}
+
+template void f<unsigned short>(char, int *); // { dg-message "required from here" }
+template void f<signed short>(char, int *);
diff --git a/gcc/testsuite/g++.dg/warn/Wduplicated-branches2.C b/gcc/testsuite/g++.dg/warn/Wduplicated-branches2.C
new file mode 100644
index 00000000000..4da2d544a1c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wduplicated-branches2.C
@@ -0,0 +1,8 @@
+// PR c/6427
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wduplicated-branches" }
+
+template<typename _ITp>
+struct S {
+  static constexpr int i = sizeof(_ITp) > alignof(_ITp) ? sizeof(_ITp) : alignof(_ITp);
+};
diff --git a/gcc/tree-core.h b/gcc/tree-core.h
index b7f8b074156..2b1759efcb1 100644
--- a/gcc/tree-core.h
+++ b/gcc/tree-core.h
@@ -814,7 +814,9 @@ enum operand_equal_flag {
   /* Internal within operand_equal_p:  */
   OEP_NO_HASH_CHECK = 16,
   /* Internal within inchash::add_expr:  */
-  OEP_HASH_CHECK = 32
+  OEP_HASH_CHECK = 32,
+  /* Makes operand_equal_p handle more expressions:  */
+  OEP_LEXICOGRAPHIC = 64
 };
 
 /* Enum and arrays used for tree allocation stats.
diff --git a/gcc/tree.c b/gcc/tree.c
index 59fe8d4aff4..7127bd265de 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -7776,7 +7776,7 @@ add_expr (const_tree t, inchash::hash &hstate, unsigned int flags)
   enum tree_code code;
   enum tree_code_class tclass;
 
-  if (t == NULL_TREE)
+  if (t == NULL_TREE || t == error_mark_node)
     {
       hstate.merge_hash (0);
       return;