[gcc r11-8599] Backported from trunk:

[gcc r11-8599] Backported from trunk:

[Martin Sebor]

https://gcc.gnu.org/g:a52b2f4cae38abecda2a7ad72a47c4e38236870a

commit r11-8599-ga52b2f4cae38abecda2a7ad72a47c4e38236870a
Author: Martin Sebor <msebor@redhat.com>
Date:   Thu Jun 17 10:20:09 2021 -0600

    Backported from trunk:
    
    PR middle-end/100250 - ICE related to -Wmaybe-uninitialized
    
    gcc/ChangeLog:
    
            PR middle-end/100250
            * attribs.c (attr_access::array_as_string): Avoid dereferencing
            a pointer when it's null.
    
    gcc/testsuite/ChangeLog:
    
            PR middle-end/100250
            * gcc.dg/uninit-pr100250.c: New test.

Diff:
---
 gcc/attribs.c                          |  3 ++-
 gcc/testsuite/gcc.dg/uninit-pr100250.c | 29 +++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/gcc/attribs.c b/gcc/attribs.c
index 3ffa1b6bc81..ebc0783c439 100644
--- a/gcc/attribs.c
+++ b/gcc/attribs.c
@@ -2388,7 +2388,8 @@ attr_access::array_as_string (tree type) const
 	  const char *p = end;
 	  for ( ; p != str && *p-- != ']'; );
 	  if (*p == '$')
-	    index_type = build_index_type (TREE_VALUE (size));
+	    /* SIZE may have been cleared.  Use it with care.  */
+	    index_type = build_index_type (size ? TREE_VALUE (size) : size);
 	}
       else if (minsize)
 	index_type = build_index_type (size_int (minsize - 1));
diff --git a/gcc/testsuite/gcc.dg/uninit-pr100250.c b/gcc/testsuite/gcc.dg/uninit-pr100250.c
new file mode 100644
index 00000000000..8e7a787ddac
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/uninit-pr100250.c
@@ -0,0 +1,29 @@
+/* PR middle-end/100250 - ICE related to -Wmaybe-uninitialized
+   { dg-do compile }
+   { dg-options "-O2 -Wall" } */
+
+extern void f (int D, const int[D], const int[D]);
+
+void g (int D, const int a[D], const int b[D], const int c[D], const int d[D])
+{
+  int c2[D];
+
+  for (int i = 0; i < D; i++) {
+
+    if (a[i] >= D) __builtin_abort ();
+    if (b[i] != d[a[i]]) __builtin_abort ();
+
+    c2[a[i]] = c[i];
+  }
+
+  f (D, d, c2);
+}
+
+void h (int D, const int d[D])
+{
+  int a[D];
+  int b[D];
+  int c[D];
+
+  g (D, a, b, c, d);          // { dg-warning "-Wmaybe-uninitialized" }
+}