RFA: ipa-devirt PATCH for c++/58678 (devirt causes KDE build failure)

[Jason Merrill]

Multiple large C++ projects (KDE and libreoffice, at least) have been 
breaking when GCC speculatively devirtualizes a call to an 
implicitly-declared virtual destructor, because this leads to references 
to base destructors and vtables that might be hidden in another DSO. 
This patch avoids this problem by avoiding speculative devirtualization 
of calls to implicitly-declared functions.

Tested x86_64-pc-linux-gnu.  OK for trunk?
commit 94eb5df9fb20c796d09151d7293ae89ac012ae79
Author: Jason Merrill <ja...@redhat.com>
Date:   Fri Feb 28 14:03:19 2014 -0500

    	PR c++/58678
    	* ipa-devirt.c (ipa_devirt): Don't choose an implicitly-declared
    	function.

diff --git a/gcc/ipa-devirt.c b/gcc/ipa-devirt.c
index 21649cb..27dc27d 100644
--- a/gcc/ipa-devirt.c
+++ b/gcc/ipa-devirt.c
@@ -1710,7 +1710,7 @@ ipa_devirt (void)
 
   int npolymorphic = 0, nspeculated = 0, nconverted = 0, ncold = 0;
   int nmultiple = 0, noverwritable = 0, ndevirtualized = 0, nnotdefined = 0;
-  int nwrong = 0, nok = 0, nexternal = 0;;
+  int nwrong = 0, nok = 0, nexternal = 0, nartificial = 0;
 
   FOR_EACH_DEFINED_FUNCTION (n)
     {	
@@ -1820,6 +1820,16 @@ ipa_devirt (void)
 		nexternal++;
 		continue;
 	      }
+	    /* Don't use an implicitly-declared destructor (c++/58678).  */
+	    struct cgraph_node *real_target
+	      = cgraph_function_node (likely_target);
+	    if (DECL_ARTIFICIAL (real_target->decl))
+	      {
+		if (dump_file)
+		  fprintf (dump_file, "Target is implicitly declared\n\n");
+		nartificial++;
+		continue;
+	      }
 	    if (cgraph_function_body_availability (likely_target)
 		<= AVAIL_OVERWRITABLE
 		&& symtab_can_be_discarded (likely_target))
@@ -1862,10 +1872,10 @@ ipa_devirt (void)
 	     " %i speculatively devirtualized, %i cold\n"
 	     "%i have multiple targets, %i overwritable,"
 	     " %i already speculated (%i agree, %i disagree),"
-	     " %i external, %i not defined\n",
+	     " %i external, %i not defined, %i artificial\n",
 	     npolymorphic, ndevirtualized, nconverted, ncold,
 	     nmultiple, noverwritable, nspeculated, nok, nwrong,
-	     nexternal, nnotdefined);
+	     nexternal, nnotdefined, nartificial);
   return ndevirtualized ? TODO_remove_functions : 0;
 }
 
diff --git a/gcc/testsuite/g++.dg/ipa/devirt-28.C b/gcc/testsuite/g++.dg/ipa/devirt-28.C
new file mode 100644
index 0000000..35c8df1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ipa/devirt-28.C
@@ -0,0 +1,17 @@
+// PR c++/58678
+// { dg-options "-O3 -fdump-ipa-devirt" }
+
+struct A {
+  virtual ~A();
+};
+struct B : A {
+  virtual int m_fn1();
+};
+void fn1(B* b) {
+  delete b;
+}
+
+// { dg-final { scan-assembler-not "_ZN1AD2Ev" } }
+// { dg-final { scan-assembler-not "_ZN1BD0Ev" } }
+// { dg-final { scan-ipa-dump "Target is implicitly declared" "devirt" } }
+// { dg-final { cleanup-ipa-dump "devirt" } }