[gcc r8-10903] c++: Fix ICE on PTRMEM_CST in lambda in inline var initializer [PR99790]

[gcc r8-10903] c++: Fix ICE on PTRMEM_CST in lambda in inline var initializer [PR99790]

[Jakub Jelinek]

https://gcc.gnu.org/g:718c32a39895ea12ff79f05d6001d7401e6e7e11

commit r8-10903-g718c32a39895ea12ff79f05d6001d7401e6e7e11
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Mar 30 18:15:32 2021 +0200

    c++: Fix ICE on PTRMEM_CST in lambda in inline var initializer [PR99790]
    
    The following testcase ICEs (since the addition of inline var support),
    because the lambda contains PTRMEM_CST but finish_function is called for the
    lambda quite early during parsing it (from finish_lambda_function) when
    the containing class is still incomplete.  That means that during
    genericization cplus_expand_constant keeps the PTRMEM_CST unmodified, but
    later nothing lowers it when the class is finalized.
    Using sizeof etc. on the class in such contexts is rejected by both g++ and
    clang++, and when the PTRMEM_CST appears e.g. in static var initializers
    rather than in functions, we handle it correctly because c_parse_final_cleanups
    -> lower_var_init will handle those cplus_expand_constant when all classes
    are already finalized.
    
    The following patch fixes it by calling cplus_expand_constant again during
    gimplification, as we are now unconditionally unit at a time, I'd think
    everything that could be completed will be before we start gimplification.
    
    2021-03-30  Jakub Jelinek  <jakub@redhat.com>
    
            PR c++/99790
            * cp-gimplify.c (cp_gimplify_expr): Handle PTRMEM_CST.
    
            * g++.dg/cpp1z/pr99790.C: New test.
    
    (cherry picked from commit 7cdd30b43a63832d6f908b2dd64bd19a0817cd7b)

Diff:
---
 gcc/cp/cp-gimplify.c                 | 8 ++++++++
 gcc/testsuite/g++.dg/cpp1z/pr99790.C | 9 +++++++++
 2 files changed, 17 insertions(+)

diff --git a/gcc/cp/cp-gimplify.c b/gcc/cp/cp-gimplify.c
index 113a46a156c..1bf887ffde4 100644
--- a/gcc/cp/cp-gimplify.c
+++ b/gcc/cp/cp-gimplify.c
@@ -839,6 +839,14 @@ cp_gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p)
 	}
       break;
 
+    case PTRMEM_CST:
+      *expr_p = cplus_expand_constant (*expr_p);
+      if (TREE_CODE (*expr_p) == PTRMEM_CST)
+	ret = GS_ERROR;
+      else
+	ret = GS_OK;
+      break;
+
     case RETURN_EXPR:
       if (TREE_OPERAND (*expr_p, 0)
 	  && (TREE_CODE (TREE_OPERAND (*expr_p, 0)) == INIT_EXPR
diff --git a/gcc/testsuite/g++.dg/cpp1z/pr99790.C b/gcc/testsuite/g++.dg/cpp1z/pr99790.C
new file mode 100644
index 00000000000..99961f5a4ee
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/pr99790.C
@@ -0,0 +1,9 @@
+// PR c++/99790
+// { dg-do compile { target c++17 } }
+
+struct A;
+struct B { void (*fn) (A *); };
+template <typename T>
+int foo (const T &);
+struct A { int a; static constexpr B b{[] (A *n) { n->*&A::a = 2; }}; };
+int a = foo (A::b);