[committed] doc: Update link to "Memory Model" paper

[Gerald Pfeifer]

The original link redirected, alas the new location gives a 404 "Not
Found". Luckily I found what looks like a more stable location.
Pushed.

Gerald



commit d15db0c5f5d81e9057df07c9568ee81873860a44
Author: Gerald Pfeifer <ger...@pfeifer.com>
Date:   Sun Mar 28 23:34:35 2021 +0200

    doc: Update link to "Memory Model" paper
    
    gcc/ChangeLog:
            * doc/analyzer.texi (Analyzer Internals): Update link to
            "A Memory Model for Static Analysis of C Programs".

diff --git a/gcc/doc/analyzer.texi b/gcc/doc/analyzer.texi
index 3f7bcf3c115..26808ff5d22 100644
--- a/gcc/doc/analyzer.texi
+++ b/gcc/doc/analyzer.texi
@@ -245,7 +245,7 @@ Merging can be disabled via 
@option{-fno-analyzer-state-merge}.
 
 Part of the state stored at a @code{exploded_node} is a @code{region_model}.
 This is an implementation of the region-based ternary model described in
-@url{http://lcs.ios.ac.cn/~xzx/memmodel.pdf,
+@url{https://www.researchgate.net/publication/221430855_A_Memory_Model_for_Static_Analysis_of_C_Programs,
 "A Memory Model for Static Analysis of C Programs"}
 (Zhongxing Xu, Ted Kremenek, and Jian Zhang).