Patchwork C++ PATCH for c++/50618 (wrong-code with virtual bases)

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Submitter Jason Merrill
Date Oct. 13, 2011, 5:56 p.m.
Message ID <4E972657.2030100@redhat.com>
Download mbox | patch
Permalink /patch/119582/
State New
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Comments

Jason Merrill - Oct. 13, 2011, 5:56 p.m.
When an object is value-initialized, if the type doesn't have a 
user-provided default constructor, the object is zero-initialized first, 
and then the synthesized constructor is called.  The problem in this PR 
was that when value-initializing a base in a constructor we were 
zero-initializing virtual bases of that base even though they had 
already been initialized properly.  The fix is to specify to 
build_zero_init_1 that we only want to clear the as-base portion of the 
type.

On the trunk I also tidied up the logic; on release branches I made the 
minimal change.  For the 4.4 branch I also needed to backport the fix 
for 48035.

Tested x86_64-pc-linux-gnu, applying to 4.4, 4.5, 4.6 and trunk.

Patch

commit fda61bbc8fd29b1df3dbeb576e0dcf806b2fcdf5
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Oct 13 13:11:31 2011 -0400

    	PR c++/50618
    	* init.c (expand_aggr_init_1): Don't zero-initialize virtual
    	bases of a base subobject.

diff --git a/gcc/cp/init.c b/gcc/cp/init.c
index c4bd635..f85a30b 100644
--- a/gcc/cp/init.c
+++ b/gcc/cp/init.c
@@ -1561,7 +1561,12 @@  expand_aggr_init_1 (tree binfo, tree true_exp, tree exp, tree init, int flags,
 	 zero out the object first.  */
       else if (TYPE_NEEDS_CONSTRUCTING (type))
 	{
-	  init = build_zero_init (type, NULL_TREE, /*static_storage_p=*/false);
+	  tree field_size = NULL_TREE;
+	  if (exp != true_exp && CLASSTYPE_AS_BASE (type) != type)
+	    /* Don't clobber already initialized virtual bases.  */
+	    field_size = TYPE_SIZE (CLASSTYPE_AS_BASE (type));
+	  init = build_zero_init_1 (type, NULL_TREE, /*static_storage_p=*/false,
+				    field_size);
 	  init = build2 (INIT_EXPR, type, exp, init);
 	  finish_expr_stmt (init);
 	  /* And then call the constructor.  */
diff --git a/gcc/testsuite/g++.dg/init/vbase1.C b/gcc/testsuite/g++.dg/init/vbase1.C
new file mode 100644
index 0000000..bbfd58f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/vbase1.C
@@ -0,0 +1,39 @@ 
+// PR c++/50618
+// { dg-do run }
+
+struct Base
+{
+    const int text;
+    Base():text(1) {}
+    Base(int aText)
+    : text(aText) {}
+};
+struct SubA : public virtual Base
+{
+protected:
+  int x;
+public:
+  SubA(int aX)
+  : x(aX) {}
+};
+class SubB : public virtual Base
+{};
+struct Diamond : public SubA, public SubB
+{
+    Diamond(int text)
+    : Base(text), SubA(5), SubB() {}
+
+    void printText()
+    {
+        if(text != 2)
+          __builtin_abort();
+        if(x!=5)
+          __builtin_abort();
+    }
+};
+
+int main(int, char**)
+{
+    Diamond x(2);
+    x.printText();
+}