[PATCH] PR c/36750: Suppress missing field initializer warning for '= {0}'

[Alexander Monakov]

Hello,

This patch suppresses the "missing field initializer" warning when a structure
is initialized with ` = { 0 }' in C.  Even though the PR author asks
specifically to suppress (at least) only when a trailing comma is included,
results from Google code search suggest that spelling without a comma is more
common, so the patch does not distinguish these variants.  Behavior of C++
front-end is unchanged.

Bootstrapped and regtested on x86_64-linux, OK for trunk?

2011-04-21  Alexander Monakov  <amona...@ispras.ru>

        PR c/36750
        * c-typeck.c (pop_init_level): Do not warn about initializing
        with ` = {0}'.

testsuite:
        * gcc.dg/missing-field-init-2.c: Update testcase.

diff --git a/gcc/c-typeck.c b/gcc/c-typeck.c
index 15b7755..d8609d2 100644
--- a/gcc/c-typeck.c
+++ b/gcc/c-typeck.c
@@ -6934,15 +6934,23 @@ pop_init_level (int implicit, struct obstack * 
braced_init_obstack)
       && TREE_CODE (constructor_type) == RECORD_TYPE
       && constructor_unfilled_fields)
     {
+       bool constructor_zeroinit =
+        (VEC_length (constructor_elt, constructor_elements) == 1
+         && integer_zerop
+             (VEC_index (constructor_elt, constructor_elements, 0)->value));
+
        /* Do not warn for flexible array members or zero-length arrays.  */
        while (constructor_unfilled_fields
               && (!DECL_SIZE (constructor_unfilled_fields)
                   || integer_zerop (DECL_SIZE (constructor_unfilled_fields))))
          constructor_unfilled_fields = DECL_CHAIN 
(constructor_unfilled_fields);
 
-       /* Do not warn if this level of the initializer uses member
-          designators; it is likely to be deliberate.  */
-       if (constructor_unfilled_fields && !constructor_designated)
+       if (constructor_unfilled_fields
+           /* Do not warn if this level of the initializer uses member
+              designators; it is likely to be deliberate.  */
+           && !constructor_designated
+           /* Do not warn about initializing with ` = {0}'.  */
+           && !constructor_zeroinit)
          {
            push_member_name (constructor_unfilled_fields);
            warning_init (OPT_Wmissing_field_initializers,
diff --git a/gcc/testsuite/gcc.dg/missing-field-init-2.c 
b/gcc/testsuite/gcc.dg/missing-field-init-2.c
index 581eb30..c5a3f49 100644
--- a/gcc/testsuite/gcc.dg/missing-field-init-2.c
+++ b/gcc/testsuite/gcc.dg/missing-field-init-2.c
@@ -9,3 +9,6 @@ struct s s4[] = { 1, 2, 3, 4, 5 }; /* { dg-warning "(missing 
initializer)|(near
 struct s s5[] = { 1, 2, 3, 4, 5, 6 };
 /* Designated initializers produce no warning.  */
 struct s s6 = { .a = 1 }; /* { dg-bogus "missing initializer" } */
+/* Allow zero-initializing with "= { 0 }".  */
+struct s s7 = { 0 }; /* { dg-bogus "missing initializer" } */
+struct s s8 = { 1 }; /* { dg-warning "(missing initializer)|(near 
initialization)" } */