[C++ Patch] PR 89488 ("[9 Regression] ICE in merge_exception_specifiers, at cp/typeck2.c:2395")

[Paolo Carlini]

Hi,

this error recovery regression has to do with the recent changes 
committed by Jason for c++/88368. What happens is that 
maybe_instantiate_noexcept fails the hard way, thus, toward the end of 
the function, doesn't update TREE_TYPE (fn) and just returns false. 
process_subob_fn doesn't notice and proceeds to call 
merge_exception_specifiers anyway where of course the gcc_assert 
(!DEFERRED_NOEXCEPT_SPEC_P (add)) triggers, because 
maybe_instantiate_noexcept has not done its normal job. To improve 
error-recovery I think we can simply leave *spec_p alone in such cases, 
because we would merge the *spec_p with a TYPE_RAISES_EXCEPTIONS 
(TREE_TYPE (fn)) where TREE_TYPE (fn) has not been normally computed. I 
tried a few other things which prima facie looked sensible but nothing 
else worked - eg, returning false from maybe_instantiate_noexcept and 
also updating TREE_TYPE (fn) to a noexcept_false_spec variant causes 
regressions exactly for the testcases of c++/88368.

Tested x86_64-linux.

Thanks, Paolo.

////////////////////////

/cp
2019-02-25  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/89488
        * method.c (process_subob_fn): When maybe_instantiate_noexcept returns
        false don't call merge_exception_specifiers.

/testsuite
2019-02-25  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/89488
        * g++.dg/cpp0x/nsdmi15.C: New.
Index: cp/method.c
===================================================================
--- cp/method.c (revision 269187)
+++ cp/method.c (working copy)
@@ -1254,9 +1254,8 @@ process_subob_fn (tree fn, tree *spec_p, bool *tri
       return;
     }
 
-  if (spec_p)
+  if (spec_p && maybe_instantiate_noexcept (fn))
     {
-      maybe_instantiate_noexcept (fn);
       tree raises = TYPE_RAISES_EXCEPTIONS (TREE_TYPE (fn));
       *spec_p = merge_exception_specifiers (*spec_p, raises);
     }
Index: testsuite/g++.dg/cpp0x/nsdmi15.C
===================================================================
--- testsuite/g++.dg/cpp0x/nsdmi15.C    (nonexistent)
+++ testsuite/g++.dg/cpp0x/nsdmi15.C    (working copy)
@@ -0,0 +1,8 @@
+// PR c++/89488
+// { dg-do compile { target c++11 } }
+
+struct zl {
+  struct {
+    int x2 = zl ();  // { dg-error "default member|cannot convert" }
+  } fx;
+};