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Re: Fix PR ipa/64693

On 01/23/2015 10:26 PM, Jan Hubicka wrote:

Hello.

Following patch is a fix for PR ipa/64693, where ICF merges a pair of functions
that somehow take a references to a different functions. Unfortunately, such function
pointer can be used for function comparison that can break an executable.

Tested on x86_64-linux-pc and no regression is added.
Apart from that, I'm able to run tests on LTO bootstraped compiler.

Ready for trunk?
Thanks,
Martin



>From ff65c1bb4ba1593ea42aec5d6cbedf2330d8a866 Mon Sep 17 00:00:00 2001
From: mliska <mliska@suse.cz>
Date: Fri, 23 Jan 2015 14:58:36 +0100
Subject: [PATCH] Fix PR ipa/64693.

gcc/ChangeLog:

2015-01-23  Martin Liska  <mliska@suse.cz>

	PR ipa/64693
	* ipa-icf.c (sem_function::equals_private): Handle references
	for a pair of compared functions.


I think you can copy a logic whether given function needs thunk - in particular
you can still merge if functions are DECL_VIRTUAL.
I also think you have same problem with variable initializers - if you merge two
variables pointing to equivalent functions that however need different addresses, you
still need to prevent merging.

Honza


Hello.

If I understand correctly, the right way would be to identify all function merge candidates
that have address taken and create a thunk. With that restriction all function comparison will
be safe.

Thanks,
Martin



gcc/testsuite/ChangeLog:

2015-01-23  Martin Liska  <mliska@suse.cz>

	* gcc.dg/ipa/ipa-icf-26.c: Fix expected results.
	* gcc.dg/ipa/ipa-icf-33.c: Remove reduced line.
	* gcc.dg/ipa/ipa-icf-34.c: New test.
---
  gcc/ipa-icf.c                         | 27 +++++++++++++++++++++-
  gcc/testsuite/gcc.dg/ipa/ipa-icf-26.c |  3 +--
  gcc/testsuite/gcc.dg/ipa/ipa-icf-33.c |  1 -
  gcc/testsuite/gcc.dg/ipa/ipa-icf-34.c | 43 +++++++++++++++++++++++++++++++++++
  4 files changed, 70 insertions(+), 4 deletions(-)
  create mode 100644 gcc/testsuite/gcc.dg/ipa/ipa-icf-34.c

diff --git a/gcc/ipa-icf.c b/gcc/ipa-icf.c
index afb5be5..4bea08d 100644
--- a/gcc/ipa-icf.c
+++ b/gcc/ipa-icf.c
@@ -525,13 +525,38 @@ sem_function::equals_private (sem_item *item,
    if (decl1 != decl2)
      return return_false();

-
    for (arg1 = DECL_ARGUMENTS (decl),
         arg2 = DECL_ARGUMENTS (m_compared_func->decl);
         arg1; arg1 = DECL_CHAIN (arg1), arg2 = DECL_CHAIN (arg2))
      if (!m_checker->compare_decl (arg1, arg2))
        return return_false ();

+  /* Compare if this function contains any function references
+     and compare them.  */
+  cgraph_node *source_node = get_node ();
+  cgraph_node *target_node = m_compared_func->get_node ();
+  if (source_node->num_references () != target_node->num_references ())
+    return return_false_with_msg ("different number of references");
+
+  ipa_ref *r1 = NULL, *r2 = NULL;
+
+  for (unsigned i = 0; i < source_node->num_references (); i++)
+    {
+      symtab_node *ref1 = source_node->iterate_reference (i, r1)->referred;
+      symtab_node *ref2 = target_node->iterate_reference (i, r2)->referred;
+
+      bool is_cgraph1 = is_a<cgraph_node *> (ref1);
+      bool is_cgraph2 = is_a<cgraph_node *> (ref2);
+
+      if (!is_cgraph1 && !is_cgraph2)
+	continue;
+
+      if ((is_cgraph1 && is_cgraph2 && ref1 != ref2)
+	  || (!is_cgraph1 && is_cgraph2)
+	  || (is_cgraph1 && !is_cgraph2))
+	return return_false_with_msg ("different target of a reference");
+    }
+
    /* Fill-up label dictionary.  */
    for (unsigned i = 0; i < bb_sorted.length (); ++i)
      {
diff --git a/gcc/testsuite/gcc.dg/ipa/ipa-icf-26.c b/gcc/testsuite/gcc.dg/ipa/ipa-icf-26.c
index 0c5a5a6..f48c040 100644
--- a/gcc/testsuite/gcc.dg/ipa/ipa-icf-26.c
+++ b/gcc/testsuite/gcc.dg/ipa/ipa-icf-26.c
@@ -38,7 +38,6 @@ int main()
    return 0;
  }

-/* { dg-final { scan-ipa-dump "Semantic equality hit:bar->foo" "icf"  } } */
  /* { dg-final { scan-ipa-dump "Semantic equality hit:remove->destroy" "icf"  } } */
-/* { dg-final { scan-ipa-dump "Equal symbols: 2" "icf"  } } */
+/* { dg-final { scan-ipa-dump "Equal symbols: 1" "icf"  } } */
  /* { dg-final { cleanup-ipa-dump "icf" } } */
diff --git a/gcc/testsuite/gcc.dg/ipa/ipa-icf-33.c b/gcc/testsuite/gcc.dg/ipa/ipa-icf-33.c
index d7e814d..7b6a8ae 100644
--- a/gcc/testsuite/gcc.dg/ipa/ipa-icf-33.c
+++ b/gcc/testsuite/gcc.dg/ipa/ipa-icf-33.c
@@ -23,5 +23,4 @@ int main()
  }

  /* { dg-final { scan-ipa-dump "Equal symbols: 1" "icf"  } } */
-/* { dg-final { scan-ipa-dump "Equal symbols: 1" "icf"  } } */
  /* { dg-final { cleanup-ipa-dump "icf" } } */
diff --git a/gcc/testsuite/gcc.dg/ipa/ipa-icf-34.c b/gcc/testsuite/gcc.dg/ipa/ipa-icf-34.c
new file mode 100644
index 0000000..c8507c7
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ipa/ipa-icf-34.c
@@ -0,0 +1,43 @@
+/* { dg-do compile } */
+/* { dg-options "-O0 -fipa-icf -fdump-ipa-icf-details"  } */
+
+#include <stdlib.h>
+#include <assert.h>
+
+int callback1(int a)
+{
+  return a * a;
+}
+
+int callback2(int a)
+{
+  return a * a;
+}
+
+static int test(int (*callback) (int))
+{
+  if (callback == callback1)
+    return 1;
+
+  return 0;
+}
+
+int foo()
+{
+  return test(&callback1);
+}
+
+int bar()
+{
+  return test(&callback2);
+}
+
+int main()
+{
+  assert (foo() != bar());
+
+  return 0;
+}
+
+/* { dg-final { scan-ipa-dump "different target of a reference" "icf"  } } */
+/* { dg-final { cleanup-ipa-dump "icf" } } */
--
2.1.2
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