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?

Jason

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