[PATCH] c++, v2: Evaluate immediate invocation call arguments with mce_true [PR119150]

[Jakub Jelinek]

On Wed, Mar 12, 2025 at 09:01:17AM -0400, Jason Merrill wrote:
> Why not use new_ctx for this instead of creating another copy?
> 
> I would think once we see that we have an immediate function, we want to go
> ahead and set ctx->manifestly_const_eval and new_call->manifestly_const_eval
> to true.  It looks like we currently cache immediate invocations separately
> depending on whether they're in an enclosing immediate function context,
> which seems redundant.
> 
> Incidentally, I don't remember why we need a separate call_ctx either.

So like this then?
Passes
GXX_TESTSUITE_STDS=98,11,14,17,20,23,26 make check-g++ 
RUNTESTFLAGS="dg.exp=consteval*"
ok if it passes full bootstrap/regtest?

2025-03-12  Jakub Jelinek  <ja...@redhat.com>

        PR c++/119150
        * constexpr.cc (cxx_eval_call_expression): For
        DECL_IMMEDIATE_FUNCTION_P (fun) set manifestly_const_eval in new_ctx
        and new_call to mce_true and set ctx to &new_ctx.

        * g++.dg/cpp2a/consteval41.C: New test.

--- gcc/cp/constexpr.cc.jj      2025-03-01 09:13:17.694075636 +0100
+++ gcc/cp/constexpr.cc 2025-03-12 16:30:29.376492168 +0100
@@ -3077,6 +3077,15 @@ cxx_eval_call_expression (const constexp
       ctx->global->put_value (new_ctx.object, ctor);
       ctx = &new_ctx;
     }
+  /* An immediate invocation is manifestly constant evaluated including the
+     arguments of the call, so use mce_true even for the argument
+     evaluation.  */
+  if (DECL_IMMEDIATE_FUNCTION_P (fun))
+    {
+      new_ctx.manifestly_const_eval = mce_true;
+      new_call.manifestly_const_eval = mce_true;
+      ctx = &new_ctx;
+    }
 
   /* We used to shortcut trivial constructor/op= here, but nowadays
      we can only get a trivial function here with -fno-elide-constructors.  */
--- gcc/testsuite/g++.dg/cpp2a/consteval41.C.jj 2025-03-07 13:39:34.526101144 
+0100
+++ gcc/testsuite/g++.dg/cpp2a/consteval41.C    2025-03-07 13:38:38.128871572 
+0100
@@ -0,0 +1,37 @@
+// PR c++/119150
+// { dg-do run { target c++20 } }
+
+consteval bool
+foo (bool x)
+{
+  return x;
+}
+
+constexpr bool
+bar ()
+{
+#if __cpp_if_consteval >= 202106L
+  if consteval
+    {
+      return true;
+    }
+  else
+    {
+      return false;
+    }
+#else
+  return __builtin_is_constant_evaluated ();
+#endif
+}
+
+int
+main ()
+{
+  bool a = false;
+  a = foo (bar ());
+  if (!a)
+    __builtin_abort ();
+  bool b = foo (bar ());
+  if (!b)
+    __builtin_abort ();
+}


        Jakub