[gcc r13-4210] Expand comment for tree_niter_desc.max

[Andrew Carlotti]

https://gcc.gnu.org/g:f80bfdcc84707583a66526fb1fb428eb66389359

commit r13-4210-gf80bfdcc84707583a66526fb1fb428eb66389359
Author: Andrew Carlotti <andrew.carlotti@arm.com>
Date:   Wed Nov 9 15:59:21 2022 +0000

    Expand comment for tree_niter_desc.max
    
    This requirement is enforced by a gcc_checking_assert in
    record_estimate.
    
    gcc/ChangeLog:
    
            * tree-ssa-loop.h (tree_niter_desc): Update comment.

Diff:
---
 gcc/tree-ssa-loop.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gcc/tree-ssa-loop.h b/gcc/tree-ssa-loop.h
index 6c70f795d17..c24215be882 100644
--- a/gcc/tree-ssa-loop.h
+++ b/gcc/tree-ssa-loop.h
@@ -52,7 +52,8 @@ public:
 			   may_be_zero == false), more precisely the number
 			   of executions of the latch of the loop.  */
   widest_int max;	/* The upper bound on the number of iterations of
-			   the loop.  */
+			   the loop.  If niter is constant, then these values
+			   must agree.  */
 
   /* The simplified shape of the exit condition.  This information is used by
      loop unrolling.  If CMP is ERROR_MARK, then the loop cannot be unrolled.