Re: [PATCH] c++: fix ICE with -Wduplicated-cond [PR107593]

[Jason Merrill via Gcc-patches]

On 1/27/23 17:15, Patrick Palka wrote:

On Thu, 26 Jan 2023, Marek Polacek via Gcc-patches wrote:

Here we crash because a CAST_EXPR, representing T(), doesn't have
its operand, and operand_equal_p's STRIP_ANY_LOCATION_WRAPPER doesn't
expect that.  (o_e_p is called from warn_duplicated_cond_add_or_warn.)

In the past we've adjusted o_e_p to better cope with template codes,
but in this case I think we just want to avoid attempting to warn
about inst-dependent expressions; I don't think I've ever envisioned
-Wduplicated-cond to warn about them.

The ICE started with r12-6022, two-stage name lookup for overloaded
operators, which gave dependent operators a TREE_TYPE (in particular,
DEPENDENT_OPERATOR_TYPE), so we no longer bail out here in o_e_p:

   /* Similar, if either does not have a type (like a template id),
      they aren't equal.  */
   if (!TREE_TYPE (arg0) || !TREE_TYPE (arg1))
     return false;

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

        PR c++/107593

gcc/cp/ChangeLog:

        * parser.cc (cp_parser_selection_statement): Don't do
        -Wduplicated-cond when the condition is dependent.

gcc/testsuite/ChangeLog:

        * g++.dg/warn/Wduplicated-cond3.C: New test.
---
  gcc/cp/parser.cc                              |  3 +-
  gcc/testsuite/g++.dg/warn/Wduplicated-cond3.C | 38 +++++++++++++++++++
  2 files changed, 40 insertions(+), 1 deletion(-)
  create mode 100644 gcc/testsuite/g++.dg/warn/Wduplicated-cond3.C

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 4cdc1cd472f..3df85d49e16 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -13209,7 +13209,8 @@ cp_parser_selection_statement (cp_parser* parser, bool 
*if_p,
            /* Add the condition.  */
            condition = finish_if_stmt_cond (condition, statement);

- if (warn_duplicated_cond)

+           if (warn_duplicated_cond
+               && !instantiation_dependent_expression_p (condition))
              warn_duplicated_cond_add_or_warn (token->location, condition,
                                                &chain);

I noticed warn_duplicated_cond_add_or_warn already has logic to handle
TREE_SIDE_EFFECTS conditions by invaliding the entire chain.  I wonder
if we'd want to do the same for instantiation-dep conditions?

Makes sense.

diff --git a/gcc/testsuite/g++.dg/warn/Wduplicated-cond3.C b/gcc/testsuite/g++.dg/warn/Wduplicated-cond3.C

new file mode 100644
index 00000000000..3da054e5485
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wduplicated-cond3.C
@@ -0,0 +1,38 @@
+// PR c++/107593
+// { dg-do compile }
+// { dg-options "-Wduplicated-cond" }
+
+template <typename T>
+void
+foo ()
+{
+  if (T() && T() && int())
+    ;
+  else if (T() && T() && int())
+    ;
+}
+
+template <typename T>
+void bar(T a)
+{
+  if (a)
+    ;
+  else if (a)
+    ;
+}
+
+template <typename>
+void baz(int a)
+{
+  if (a)
+    ;
+  else if (a) // { dg-warning "duplicated" }
+    ;
+}
+void
+f ()
+{
+  foo<int>();
+  bar(1);
+  baz<int>(1);
+}

base-commit: 94673a121cfc7f9d51c9d05e31795477f4dc8dc7
--
2.39.1