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Fix devirtualiation in expanded thunks


Hi,
this patch fixes polymorphic call analysis in thunks.  Unlike normal
methods, thunks take THIS pointer offsetted by a known constant. This
needs t be compensated for when calculating address of outer type.

Bootstrapped/regtested x86_64-linux, also tested with Firefox where this
bug trigger misoptimization in spellchecker.  I plan to backport it to
release branches soon.

Honza

	PR ipa/88561
	* ipa-polymorphic-call.c
	(ipa_polymorphic_call_context::ipa_polymorphic_call_context): Handle
	arguments of thunks correctly.
	(ipa_polymorphic_call_context::get_dynamic_context): Be ready for
	NULL instance pinter.
	* lto-cgraph.c (lto_output_node): Always stream thunk info.
	* g++.dg/tree-prof/devirt.C: New testcase.
Index: ipa-polymorphic-call.c
===================================================================
--- ipa-polymorphic-call.c	(revision 267325)
+++ ipa-polymorphic-call.c	(working copy)
@@ -995,9 +995,22 @@ ipa_polymorphic_call_context::ipa_polymo
 	{
 	  outer_type
 	     = TYPE_MAIN_VARIANT (TREE_TYPE (TREE_TYPE (base_pointer)));
+	  cgraph_node *node = cgraph_node::get (current_function_decl);
 	  gcc_assert (TREE_CODE (outer_type) == RECORD_TYPE
 		      || TREE_CODE (outer_type) == UNION_TYPE);
 
+	  /* Handle the case we inlined into a thunk.  In this case
+	     thunk has THIS pointer of type bar, but it really receives
+	     address to its base type foo which sits in bar at 
+	     0-thunk.fixed_offset.  It starts with code that adds
+	     think.fixed_offset to the pointer to compensate for this.
+
+	     Because we walked all the way to the begining of thunk, we now
+	     see pointer &bar-thunk.fixed_offset and need to compensate
+	     for it.  */
+	  if (node->thunk.fixed_offset)
+	    offset -= node->thunk.fixed_offset * BITS_PER_UNIT;
+
 	  /* Dynamic casting has possibly upcasted the type
 	     in the hiearchy.  In this case outer type is less
 	     informative than inner type and we should forget
@@ -1005,7 +1018,11 @@ ipa_polymorphic_call_context::ipa_polymo
 	  if ((otr_type
 	       && !contains_type_p (outer_type, offset,
 				    otr_type))
-	      || !contains_polymorphic_type_p (outer_type))
+	      || !contains_polymorphic_type_p (outer_type)
+	      /* If we compile thunk with virtual offset, the THIS pointer
+		 is adjusted by unknown value.  We can't thus use outer info
+		 at all.  */
+	      || node->thunk.virtual_offset_p)
 	    {
 	      outer_type = NULL;
 	      if (instance)
@@ -1030,7 +1047,15 @@ ipa_polymorphic_call_context::ipa_polymo
 	      maybe_in_construction = false;
 	    }
 	  if (instance)
-	    *instance = base_pointer;
+	    {
+	      /* If method is expanded thunk, we need to apply thunk offset
+		 to instance pointer.  */
+	      if (node->thunk.virtual_offset_p
+		  || node->thunk.fixed_offset)
+		*instance = NULL;
+	      else
+	        *instance = base_pointer;
+	    }
 	  return;
 	}
       /* Non-PODs passed by value are really passed by invisible
@@ -1547,6 +1572,9 @@ ipa_polymorphic_call_context::get_dynami
   HOST_WIDE_INT instance_offset = offset;
   tree instance_outer_type = outer_type;
 
+  if (!instance)
+    return false;
+
   if (otr_type)
     otr_type = TYPE_MAIN_VARIANT (otr_type);
 
Index: lto-cgraph.c
===================================================================
--- lto-cgraph.c	(revision 267325)
+++ lto-cgraph.c	(working copy)
@@ -547,7 +547,11 @@ lto_output_node (struct lto_simple_outpu
   streamer_write_bitpack (&bp);
   streamer_write_data_stream (ob->main_stream, section, strlen (section) + 1);
 
-  if (node->thunk.thunk_p)
+  /* Stream thunk info always because we use it in
+     ipa_polymorphic_call_context::ipa_polymorphic_call_context
+     to properly interpret THIS pointers for thunks that has been converted
+     to Gimple.  */
+  if (node->definition)
     {
       streamer_write_uhwi_stream
 	 (ob->main_stream,
@@ -1295,7 +1299,7 @@ input_node (struct lto_file_decl_data *f
   if (section)
     node->set_section_for_node (section);
 
-  if (node->thunk.thunk_p)
+  if (node->definition)
     {
       int type = streamer_read_uhwi (ib);
       HOST_WIDE_INT fixed_offset = streamer_read_uhwi (ib);
Index: testsuite/g++.dg/tree-prof/devirt.C
===================================================================
--- testsuite/g++.dg/tree-prof/devirt.C	(nonexistent)
+++ testsuite/g++.dg/tree-prof/devirt.C	(working copy)
@@ -0,0 +1,123 @@
+/* { dg-options "-O3 -fdump-tree-dom3" } */
+struct nsISupports
+{
+  virtual int QueryInterface (const int &aIID, void **aInstancePtr) = 0;
+  virtual __attribute__((noinline, noclone)) unsigned AddRef (void) = 0;
+  virtual unsigned Release (void) = 0;
+};
+
+struct nsIObserver : public nsISupports
+{
+  virtual int Observe (nsISupports * aSubject, const char *aTopic, const unsigned short *aData) = 0;
+};
+
+struct nsISupportsWeakReference : public nsISupports
+{
+  virtual int GetWeakReference (void **_retval) = 0;
+};
+
+struct nsSupportsWeakReference : public nsISupportsWeakReference
+{
+  nsSupportsWeakReference () : mProxy (0) {}
+  virtual int GetWeakReference (void **_retval) override { return 0; }
+  ~nsSupportsWeakReference () {}
+  void NoticeProxyDestruction () { mProxy = nullptr; }
+  void *mProxy;
+  void ClearWeakReferences ();
+  bool HasWeakReferences () const { return !!mProxy; }
+};
+
+struct mozIPersonalDictionary : public nsISupports
+{
+  virtual int Load (void) = 0;
+  virtual int Save (void) = 0;
+  virtual int GetWordList (void **aWordList) = 0;
+  virtual int Check (const int &word, bool * _retval) = 0;
+  virtual int AddWord (const int &word) = 0;
+  virtual int RemoveWord (const int &word) = 0;
+  virtual int IgnoreWord (const int &word) = 0;
+  virtual int EndSession (void) = 0;
+};
+
+struct mozPersonalDictionary final
+  : public mozIPersonalDictionary, public nsIObserver, public nsSupportsWeakReference
+{
+  virtual int QueryInterface (const int &aIID, void **aInstancePtr) override;
+  virtual __attribute__((noinline, noclone)) unsigned AddRef (void) override;
+  virtual unsigned Release (void) override;
+  unsigned long mRefCnt;
+  virtual int Load (void) override { return 0; }
+  virtual int Save (void) override { return 0; }
+  virtual int GetWordList (void **aWordList) override { return 0; }
+  virtual int Check (const int &word, bool * _retval) override { return 0; }
+  virtual int AddWord (const int &word) override { return 0; }
+  virtual int RemoveWord (const int &word) override { return 0; }
+  virtual int IgnoreWord (const int &word) override { return 0; }
+  virtual int EndSession (void) override { return 0; }
+  virtual int Observe (nsISupports * aSubject, const char *aTopic, const unsigned short *aData) override { return 0; }
+  mozPersonalDictionary () : mRefCnt(0) {}
+  int Init () { return 0; }
+  virtual ~mozPersonalDictionary () {}
+  bool mIsLoaded;
+  bool mSavePending;
+  void *mFile;
+  char mMonitor[96];
+  char mMonitorSave[96];
+  char mDictionaryTable[32];
+  char mIgnoreTable[32];
+};
+
+unsigned
+mozPersonalDictionary::AddRef (void)
+{
+  unsigned count = ++mRefCnt;
+  return count;
+}
+
+unsigned
+mozPersonalDictionary::Release (void)
+{
+  unsigned count = --mRefCnt;
+  if (count == 0)
+    {
+      mRefCnt = 1;
+      delete (this);
+      return 0;
+    }
+  return count;
+}
+
+int
+mozPersonalDictionary::QueryInterface (const int &aIID, void **aInstancePtr)
+{
+  nsISupports *foundInterface;
+  if (aIID == 122)
+    foundInterface = static_cast <mozIPersonalDictionary *>(this);
+  else
+    foundInterface = static_cast <nsISupportsWeakReference *>(this);
+  int status;
+  foundInterface->AddRef ();
+  *aInstancePtr = foundInterface;
+  return status;
+}
+
+__attribute__((noipa)) int
+foo (nsISupports *p, const int &i)
+{
+  void *q;
+  return p->QueryInterface (i, &q);
+}
+
+int
+main ()
+{
+  mozPersonalDictionary m;
+  int j = 123;
+  for (int i = 0; i < 100000; i++)
+    foo (static_cast <nsISupportsWeakReference *>(&m), j);
+  if (m.mRefCnt != 100000)
+    __builtin_abort ();
+}
+
+/* { dg-final-use-not-autofdo { scan-ipa-dump-times 3 "folding virtual function call to virtual unsigned int mozPersonalDictionary::_ZThn16" "dom3" } } */
+/* { dg-final-use-not-autofdo { scan-ipa-dump-times 3 "folding virtual function call to virtual unsigned int mozPersonalDictionary::AddRef" "dom3" } } */


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