[PATCH] Fix PR54515

[Markus Trippelsdorf]

Here the problem is that get_base_address() can return NULL_TREE and
this later leads to a segfault. Fix by checking that the return value is
valid.
gcc-4.6 and 4.7 are also affected.

Please commit if this looks OK.
Thanks.

Tested on x86_64-pc-linux-gnu

2012-09-07  Markus Trippelsdorf  <mar...@trippelsdorf.de>

        PR middle-end/54515
        * tree-sra.c (disqualify_base_of_expr): Check for possible
        NULL_TREE returned by get_base_address()

        * g++.dg/tree-ssa/pr54515.C: new testcase

diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr54515.C 
b/gcc/testsuite/g++.dg/tree-ssa/pr54515.C
new file mode 100644
index 0000000..11ed468
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/pr54515.C
@@ -0,0 +1,19 @@
+// { dg-do compile }
+// { dg-options "-O2" }
+
+template < typename T > T h2le (T)
+{
+    T a;
+    unsigned short &b = a;
+    short c = 0;
+    unsigned char (&d)[2] = reinterpret_cast < unsigned char (&)[2] > (c);
+    unsigned char (&e)[2] = reinterpret_cast < unsigned char (&)[2] > (b);
+    e[0] = d[0];
+    return a;
+}
+
+void
+bar ()
+{
+    h2le ((unsigned short) 0);
+}
diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
index aafaa15..2bb92e9 100644
--- a/gcc/tree-sra.c
+++ b/gcc/tree-sra.c
@@ -984,7 +984,8 @@ static void
 disqualify_base_of_expr (tree t, const char *reason)
 {
   t = get_base_address (t);
-  if (sra_mode == SRA_MODE_EARLY_IPA
+  if (t
+      && sra_mode == SRA_MODE_EARLY_IPA
       && TREE_CODE (t) == MEM_REF)
     t = get_ssa_base_param (TREE_OPERAND (t, 0));
 
-- 
Markus