[pushed] c++: consteval propagation and templates [PR115986]

[Jason Merrill]

Tested x86_64-pc-linux-gnu, applying to trunk.

-- 8< --

Here the call to e() makes us decide to check d() for escalation at EOF, but
while checking it we try to fold_immediate 0_c, and get confused by the
template trees.  Let's not mess with escalation for function templates.

        PR c++/115986

gcc/cp/ChangeLog:

        * cp-gimplify.cc (remember_escalating_expr): Skip function
        templates.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp2a/consteval-prop21.C: New test.
---
 gcc/cp/cp-gimplify.cc                         |  4 ++++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop21.C | 17 +++++++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop21.C

diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
index e6629dea5fd..6a5e4cf62ca 100644
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@@ -53,6 +53,10 @@ static GTY(()) hash_set<tree> *deferred_escalating_exprs;
 static void
 remember_escalating_expr (tree t)
 {
+  if (uses_template_parms (t))
+    /* Templates don't escalate, and cp_fold_immediate can get confused by
+       other template trees in the function body (c++/115986).  */
+    return;
   if (!deferred_escalating_exprs)
     deferred_escalating_exprs = hash_set<tree>::create_ggc (37);
   deferred_escalating_exprs->add (t);
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop21.C 
b/gcc/testsuite/g++.dg/cpp2a/consteval-prop21.C
new file mode 100644
index 00000000000..debbda4f425
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop21.C
@@ -0,0 +1,17 @@
+// PR c++/115986
+// { dg-do compile { target c++20 } }
+
+template <typename T>
+constexpr int b(T) {
+  return 0;
+}
+consteval __uint128_t operator"" _c(const char*) { return 0; }
+constexpr char e() {
+  long f = true ? 0 : b(long(1));
+  return b(f);
+}
+template <typename>
+void d() {
+  0_c;
+  static_assert(e());
+}

base-commit: 928116e94a5a8a995dffd926af58abfa7286e78e
-- 
2.45.2