C PATCH to add -Woverride-init-side-effects (PR c/64918)

[Marek Polacek <polacek at redhat dot com>]

As discussed in the PR, the "initialized field with side-effects overwritten"
warning is sometimes not so useful, so it probably makes sense to provide an
option so that users are able to specifically enable/disable it.  Since the
warning is enabled by default at present, it is enabled by default even with
this patch, unlike -Woverride-init, which is in -Wextra. 

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2015-04-24  Marek Polacek  <polacek@redhat.com>

	PR c/64918
	* c.opt (Woverride-init-side-effects): New option.

	* c-typeck.c (add_pending_init): Use OPT_Woverride_init_side_effects.
	(output_init_element): Likewise.

	* doc/invoke.texi: Document -Woverride-init-side-effects.

	* gcc.dg/Woverride-init-side-effects-1.c: New test.
	* gcc.dg/Woverride-init-side-effects-2.c: New test.

diff --git gcc/c-family/c.opt gcc/c-family/c.opt
index 983f4a8..50dc8ec 100644
--- gcc/c-family/c.opt
+++ gcc/c-family/c.opt
@@ -709,6 +709,10 @@ Woverride-init
 C ObjC Var(warn_override_init) Warning EnabledBy(Wextra)
 Warn about overriding initializers without side effects
 
+Woverride-init-side-effects
+C ObjC Var(warn_override_init_side_effects) Init(1) Warning
+Warn about overriding initializers with side effects
+
 Wpacked-bitfield-compat
 C ObjC C++ ObjC++ Var(warn_packed_bitfield_compat) Init(-1) Warning
 Warn about packed bit-fields whose offset changed in GCC 4.4
diff --git gcc/c/c-typeck.c gcc/c/c-typeck.c
index 91735b5..635b568 100644
--- gcc/c/c-typeck.c
+++ gcc/c/c-typeck.c
@@ -7978,7 +7978,7 @@ add_pending_init (location_t loc, tree purpose, tree value, tree origtype,
 	      if (!implicit)
 		{
 		  if (TREE_SIDE_EFFECTS (p->value))
-		    warning_init (loc, 0,
+		    warning_init (loc, OPT_Woverride_init_side_effects,
 				  "initialized field with side-effects "
 				  "overwritten");
 		  else if (warn_override_init)
@@ -8008,7 +8008,7 @@ add_pending_init (location_t loc, tree purpose, tree value, tree origtype,
 	      if (!implicit)
 		{
 		  if (TREE_SIDE_EFFECTS (p->value))
-		    warning_init (loc, 0,
+		    warning_init (loc, OPT_Woverride_init_side_effects,
 				  "initialized field with side-effects "
 				  "overwritten");
 		  else if (warn_override_init)
@@ -8540,7 +8540,7 @@ output_init_element (location_t loc, tree value, tree origtype,
       if (!implicit)
 	{
 	  if (TREE_SIDE_EFFECTS (constructor_elements->last ().value))
-	    warning_init (loc, 0,
+	    warning_init (loc, OPT_Woverride_init_side_effects,
 			  "initialized field with side-effects overwritten");
 	  else if (warn_override_init)
 	    warning_init (loc, OPT_Woverride_init,
diff --git gcc/doc/invoke.texi gcc/doc/invoke.texi
index a939ff7..ff2ff24 100644
--- gcc/doc/invoke.texi
+++ gcc/doc/invoke.texi
@@ -266,6 +266,7 @@ Objective-C and Objective-C++ Dialects}.
 -Wmissing-field-initializers -Wmissing-include-dirs @gol
 -Wno-multichar  -Wnonnull  -Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} @gol
 -Wodr  -Wno-overflow  -Wopenmp-simd @gol
+-Woverride-init-side-effects @gol
 -Woverlength-strings  -Wpacked  -Wpacked-bitfield-compat  -Wpadded @gol
 -Wparentheses  -Wpedantic-ms-format -Wno-pedantic-ms-format @gol
 -Wpointer-arith  -Wno-pointer-to-int-cast @gol
@@ -5177,6 +5178,13 @@ This warning is included in @option{-Wextra}.  To get other
 @option{-Wextra} warnings without this one, use @option{-Wextra
 -Wno-override-init}.
 
+@item -Woverride-init-side-effects @r{(C and Objective-C only)}
+@opindex Woverride-init-side-effects
+@opindex Wno-override-init-side-effects
+Warn if an initialized field with side effects is overridden when
+using designated initializers (@pxref{Designated Inits, , Designated
+Initializers}).  This warning is enabled by default.
+
 @item -Wpacked
 @opindex Wpacked
 @opindex Wno-packed
diff --git gcc/testsuite/gcc.dg/Woverride-init-side-effects-1.c gcc/testsuite/gcc.dg/Woverride-init-side-effects-1.c
index e69de29..50f198d 100644
--- gcc/testsuite/gcc.dg/Woverride-init-side-effects-1.c
+++ gcc/testsuite/gcc.dg/Woverride-init-side-effects-1.c
@@ -0,0 +1,25 @@
+/* PR c/64918 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+struct S { int m, n; };
+union U { short s; long int l; };
+
+void
+foo (int i)
+{
+  int a[] = {
+    [0] = ++i,
+    [1] = i,
+    [0] = 42	/* { dg-warning "initialized field with side-effects overwritten" } */
+  };
+  struct S s = {
+    .n = ++i,
+    .m = i,
+    .n = i	/* { dg-warning "initialized field with side-effects overwritten" } */
+  };
+  union U u = {
+    .s = i--,
+    .l = 42	/* { dg-warning "initialized field with side-effects overwritten" } */
+  };
+}
diff --git gcc/testsuite/gcc.dg/Woverride-init-side-effects-2.c gcc/testsuite/gcc.dg/Woverride-init-side-effects-2.c
index e69de29..a64e96a 100644
--- gcc/testsuite/gcc.dg/Woverride-init-side-effects-2.c
+++ gcc/testsuite/gcc.dg/Woverride-init-side-effects-2.c
@@ -0,0 +1,25 @@
+/* PR c/64918 */
+/* { dg-do compile } */
+/* { dg-options "-Wno-override-init-side-effects" } */
+
+struct S { int m, n; };
+union U { short s; long int l; };
+
+void
+foo (int i)
+{
+  int a[] = {
+    [0] = ++i,
+    [1] = i,
+    [0] = 42
+  };
+  struct S s = {
+    .n = ++i,
+    .m = i,
+    .n = i
+  };
+  union U u = {
+    .s = i--,
+    .l = 42
+  };
+}

	Marek