On 9/18/23 08:58, Patrick Palka wrote:
On Sun, 17 Sep 2023, Jason Merrill wrote:

On 9/17/23 15:13, Patrick Palka wrote:
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?

-- >8 --

r14-2655-g92d1425ca78040 made instantiate_template avoid redundantly
performing a specialization lookup when instantiating a function or
alias template.  This patch applies the same optimization to
tsubst_template_decl when (partially) instantiating a function template,
which allows us to remove a check from register_specialization since
tsubst_function_decl no longer calls register_specialization for
a function template partial instantiation.

gcc/cp/ChangeLog:

        * pt.cc (register_specialization): Remove now-unnecessary
        early exit for FUNCTION_DECL partial instantiation.
        (tsubst_template_decl): Pass use_spec_table=false to
        tsubst_function_decl.  Set DECL_TI_ARGS of a non-lambda
        FUNCTION_DECL specialization to the full set of arguments.
        Simplify register_specialization call accordingly.

gcc/testsuite/ChangeLog:

        * g++.dg/template/nontype12.C: Expect two instead of three
        duplicate diagnostics for A<double>::bar() specialization.
---
   gcc/cp/pt.cc                              | 29 +++++++----------------
   gcc/testsuite/g++.dg/template/nontype12.C |  1 -
   2 files changed, 9 insertions(+), 21 deletions(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index c311a6b88f5..a0296a1ea16 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -1507,21 +1507,6 @@ register_specialization (tree spec, tree tmpl, tree
args, bool is_friend,
              || (TREE_CODE (tmpl) == FIELD_DECL
                  && TREE_CODE (spec) == NONTYPE_ARGUMENT_PACK));
   -  if (TREE_CODE (spec) == FUNCTION_DECL
-      && uses_template_parms (DECL_TI_ARGS (spec)))
-    /* This is the FUNCTION_DECL for a partial instantiation.  Don't
-       register it; we want the corresponding TEMPLATE_DECL instead.
-       We use `uses_template_parms (DECL_TI_ARGS (spec))' rather than
-       the more obvious `uses_template_parms (spec)' to avoid problems
-       with default function arguments.  In particular, given
-       something like this:
-
-         template <class T> void f(T t1, T t = T())
-
-       the default argument expression is not substituted for in an
-       instantiation unless and until it is actually needed.  */
-    return spec;
-
     spec_entry elt;
     elt.tmpl = tmpl;
     elt.args = args;
@@ -14663,7 +14648,7 @@ tsubst_template_decl (tree t, tree args,
tsubst_flags_t complain,
     tree in_decl = t;
     tree spec;
     tree tmpl_args;
-  tree full_args;
+  tree full_args = NULL_TREE;
     tree r;
     hashval_t hash = 0;
   @@ -14754,7 +14739,8 @@ tsubst_template_decl (tree t, tree args,
tsubst_flags_t complain,
     tree inner = decl;
     ++processing_template_decl;
     if (TREE_CODE (inner) == FUNCTION_DECL)
-    inner = tsubst_function_decl (inner, args, complain, lambda_fntype);
+    inner = tsubst_function_decl (inner, args, complain, lambda_fntype,
+                                 /*use_spec_table=*/false);
     else
       {
         if (TREE_CODE (inner) == TYPE_DECL && !TYPE_DECL_ALIAS_P (inner))
@@ -14792,6 +14778,11 @@ tsubst_template_decl (tree t, tree args,
tsubst_flags_t complain,
       }
     else
       {
+      if (TREE_CODE (inner) == FUNCTION_DECL)
+       /* Set DECL_TI_ARGS to the full set of template arguments, which
+          tsubst_function_decl didn't do due to use_spec_table=false.  */
+       DECL_TI_ARGS (inner) = full_args;
+
         DECL_TI_TEMPLATE (inner) = r;
         DECL_TI_ARGS (r) = DECL_TI_ARGS (inner);
       }
@@ -14822,9 +14813,7 @@ tsubst_template_decl (tree t, tree args,
tsubst_flags_t complain,
       if (TREE_CODE (decl) == FUNCTION_DECL && !lambda_fntype)
       /* Record this non-type partial instantiation.  */
-    register_specialization (r, t,
-                            DECL_TI_ARGS (DECL_TEMPLATE_RESULT (r)),
-                            false, hash);
+    register_specialization (r, t, full_args, false, hash);
       return r;
   }
diff --git a/gcc/testsuite/g++.dg/template/nontype12.C
b/gcc/testsuite/g++.dg/template/nontype12.C
index 9a9c3ac1e66..e36a9f16f94 100644
--- a/gcc/testsuite/g++.dg/template/nontype12.C
+++ b/gcc/testsuite/g++.dg/template/nontype12.C
@@ -5,7 +5,6 @@ template<typename T> struct A
   {
     template<T> int foo();                        // { dg-error "double" ""
{ target c++17_down } }
     template<template<T> class> int bar();        // { dg-bogus
{double[^\n]*\n[^\n]*C:7:[^\n]*double} "" { xfail c++17_down } }
-  // { dg-error "double" "" { target c++17_down } .-1 }

Hmm, I thought this line was to check that we get one error even if we don't
want two?

The xfailed dg-bogus directive seems to "consume" the two errors, and
prevents the dg-error from matching either of them.  Before this patch,
we issued three duplicate errors and so this arrangement worked out
since the xfailed dg-bogus consumes only two of the errors.  I'm not
sure how to express that we're currently seeing two errors but only want
one using _both_ dg-error and dg-bogus..

Would it work to have a dg-error to consume one error followed by a dg-bogus for another single error?

If not, just add a comment.  OK either way.

Jason

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