[gcc r12-7797] fold-const: Handle C++ dependent COMPONENT_REFs in operand_equal_p [PR105035]

[Jakub Jelinek <jakub@gcc.gnu.org>]

https://gcc.gnu.org/g:8698ff67cdff4364c8adad2921ed532359a155ec

commit r12-7797-g8698ff67cdff4364c8adad2921ed532359a155ec
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Mar 24 12:23:51 2022 +0100

    fold-const: Handle C++ dependent COMPONENT_REFs in operand_equal_p [PR105035]
    
    As mentioned in the PR, operand_equal_p already contains some hacks so that
    it can be called already on pre-instantiation C++ trees from templates,
    but the recent change to compare DECL_FIELD_OFFSET in the COMPONENT_REF
    case broke this.  Many such COMPONENT_REFs are already punted on earlier
    because they have NULL TREE_TYPE, but in this case the code knows what
    type they have but still uses an IDENTIFIER_NODE as second operand
    of COMPONENT_REF (I think SCOPE_REF is something that could be used too).
    
    The following patch looks at those DECL_FIELD_*OFFSET fields only if
    both field[01] args are FIELD_DECLs and otherwise keeps it to the
    earlier OP_SAME (1) check that guards this whole block.
    
    2022-03-24  Jakub Jelinek  <jakub@redhat.com>
    
            PR c++/105035
            * fold-const.cc (operand_equal_p) <case COMPONENT_REF>: If either
            field0 or field1 is not a FIELD_DECL, return false.
    
            * g++.dg/warn/Wduplicated-cond2.C: New test.

Diff:
---
 gcc/fold-const.cc                             |  7 +++++--
 gcc/testsuite/g++.dg/warn/Wduplicated-cond2.C | 29 +++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 39a5a52958d..b647e5305aa 100644
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -3357,8 +3357,11 @@ operand_compare::operand_equal_p (const_tree arg0, const_tree arg1,
 		    tree field0 = TREE_OPERAND (arg0, 1);
 		    tree field1 = TREE_OPERAND (arg1, 1);
 
-		    if (!operand_equal_p (DECL_FIELD_OFFSET (field0),
-					  DECL_FIELD_OFFSET (field1), flags)
+		    /* Non-FIELD_DECL operands can appear in C++ templates.  */
+		    if (TREE_CODE (field0) != FIELD_DECL
+			|| TREE_CODE (field1) != FIELD_DECL
+			|| !operand_equal_p (DECL_FIELD_OFFSET (field0),
+					     DECL_FIELD_OFFSET (field1), flags)
 			|| !operand_equal_p (DECL_FIELD_BIT_OFFSET (field0),
 					     DECL_FIELD_BIT_OFFSET (field1),
 					     flags))
diff --git a/gcc/testsuite/g++.dg/warn/Wduplicated-cond2.C b/gcc/testsuite/g++.dg/warn/Wduplicated-cond2.C
new file mode 100644
index 00000000000..c977389a2e4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wduplicated-cond2.C
@@ -0,0 +1,29 @@
+// PR c++/105035
+// { dg-do compile }
+// { dg-options "-Wduplicated-cond" }
+
+class A {
+  struct B { int c; int f; } e;
+  template <typename> void foo ();
+  void bar ();
+};
+
+template <typename> void
+A::foo ()
+{
+  int g;
+  if (&g == &e.c)
+    ;
+  else if (&g == &e.f)
+    ;
+}
+
+void
+A::bar ()
+{
+  int g;
+  if (&g == &e.c)	// { dg-message "previously used here" }
+    ;
+  else if (&g == &e.c)	// { dg-warning "duplicated 'if' condition" }
+    ;
+}