Re: [PATCH] c++: ICE with constexpr call that returns a PMF [PR98551]

[Jason Merrill via Gcc-patches]

On 1/7/21 10:10 AM, Patrick Palka wrote:
We shouldn't do replace_result_decl after evaluating a call that returns
a PMF because PMF temporaries aren't wrapped in a TARGET_EXPR (and so we
can't trust ctx->object), and PMF initializers can't be self-referential
anyway, so replace_result_decl would always be a no-op.  This fixes an
ICE from the sanity check in replace_result_decl in the below testcase
during cxx_eval_call_expression of the call f() in the initializer g(f()).
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?

gcc/cp/ChangeLog:

        PR c++/98551
        * constexpr.c (cxx_eval_call_expression): Don't call
        replace_result_decl when the result is a PMF.

gcc/testsuite/ChangeLog:

        PR c++/98551
        * g++.dg/cpp0x/constexpr-pmf2.C: New test.
---
  gcc/cp/constexpr.c                          | 1 +
  gcc/testsuite/g++.dg/cpp0x/constexpr-pmf2.C | 9 +++++++++
  2 files changed, 10 insertions(+)
  create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-pmf2.C

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 0c12f608d36..a7272d49d0d 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -2788,6 +2788,7 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree 
t,
               current object under construction.  */
            if (!*non_constant_p && ctx->object
                && AGGREGATE_TYPE_P (TREE_TYPE (res))
+               && !TYPE_PTRMEMFUNC_P (TREE_TYPE (res))

It ought to work to change AGGREGATE_TYPE_P to CLASS_TYPE_P; we can't 
return an array, and a vector can't contain a pointer to itself.

Alternately, we could change the same-type assert in replace_result_decl 
to a test and return false if different.

OK with either change.

                && !is_empty_class (TREE_TYPE (res)))
              if (replace_result_decl (&result, res, ctx->object))
                cacheable = false;
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-pmf2.C 
b/gcc/testsuite/g++.dg/cpp0x/constexpr-pmf2.C
new file mode 100644
index 00000000000..a76e712afe1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-pmf2.C
@@ -0,0 +1,9 @@
+// PR c++/98551
+// { dg-do compile { target c++11 } }
+
+struct A {};
+struct B { int t(); };
+using pmf = decltype(&B::t);
+constexpr pmf f() { return &B::t; }
+constexpr A g(pmf) { return {}; };
+constexpr A x = g(f());