[gcc r13-4926] [C++] constexpr: request insert iff depth is ok

[gcc r13-4926] [C++] constexpr: request insert iff depth is ok

[Alexandre Oliva]

https://gcc.gnu.org/g:6ec8079e0b7dc7c44a7001ffb20ca038362191d5

commit r13-4926-g6ec8079e0b7dc7c44a7001ffb20ca038362191d5
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Thu Dec 29 14:32:59 2022 -0300

    [C++] constexpr: request insert iff depth is ok
    
    cxx_eval_call_expression requests an INSERT even in cases when it
    would later decide not to insert.  This could break double-hashing
    chains.  Arrange for it to use NO_INSERT when the insertion would not
    be completed.
    
    
    for  gcc/cp/ChangeLog
    
            * constexpr.cc (cxx_eval_call_expression): Do not request an
            INSERT that would not be completed.

Diff:
---
 gcc/cp/constexpr.cc | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 414af7a6d4c..a65dbdc5b13 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -3000,13 +3000,15 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t,
 
       /* If we have seen this call before, we are done.  */
       maybe_initialize_constexpr_call_table ();
+      bool insert = depth_ok < constexpr_cache_depth;
       constexpr_call **slot
-	= constexpr_call_table->find_slot (&new_call, INSERT);
-      entry = *slot;
+	= constexpr_call_table->find_slot (&new_call,
+					   insert ? INSERT : NO_INSERT);
+      entry = slot ? *slot : NULL;
       if (entry == NULL)
 	{
 	  /* Only cache up to constexpr_cache_depth to limit memory use.  */
-	  if (depth_ok < constexpr_cache_depth)
+	  if (insert)
 	    {
 	      /* We need to keep a pointer to the entry, not just the slot, as
 		 the slot can move during evaluation of the body.  */