[gcc r11-4620] core: Synchronize tree-cst & wide-int caching expectations

[gcc r11-4620] core: Synchronize tree-cst & wide-int caching expectations

[Nathan Sidwell]

https://gcc.gnu.org/g:a0bc61e0b6da2ff9aca05d7b389a9c114a034052

commit r11-4620-ga0bc61e0b6da2ff9aca05d7b389a9c114a034052
Author: Nathan Sidwell <nathan@acm.org>
Date:   Mon Nov 2 08:46:16 2020 -0800

    core: Synchronize tree-cst & wide-int caching expectations
    
    I fell over an ICE where wide_int_to_type_1's expectations of pointer
    value caching didn't match that of cache_integer_cst's behaviour.  I
    don't know why it only exhibited on the modules branch, but it seems
    pretty wrong.  This patch matches up the behaviours and adds a comment
    about that.
    
            gcc/
            * tree.c (cache_integer_cst): Fixup pointer caching to match
            wide_int_to_type_1's expectations.  Add comment.

Diff:
---
 gcc/tree.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/gcc/tree.c b/gcc/tree.c
index 739c288378a..9260772b846 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -1737,6 +1737,8 @@ cache_integer_cst (tree t)
 
   gcc_assert (!TREE_OVERFLOW (t));
 
+  /* The caching indices here must match those in
+     wide_int_to_type_1.  */
   switch (TREE_CODE (type))
     {
     case NULLPTR_TYPE:
@@ -1745,12 +1747,15 @@ cache_integer_cst (tree t)
 
     case POINTER_TYPE:
     case REFERENCE_TYPE:
-      /* Cache NULL pointer.  */
-      if (integer_zerop (t))
-	{
-	  limit = 1;
+      {
+	if (integer_zerop (t))
 	  ix = 0;
-	}
+	else if (integer_onep (t))
+	  ix = 2;
+
+	if (ix >= 0)
+	  limit = 3;
+      }
       break;
 
     case BOOLEAN_TYPE: