[PR middle-end/78328] [committed] wrong wording for unbounded alloca case

[Aldy Hernandez]

The problem here is that as we follow the cast from an unsigned int to 
__SIZE_TYPE__, we ignore the VR_ANTI_RANGE of 7 exhibited by the test in 
the PR:

+void g (unsigned int n)
+{
+  if (n == 7)
+    n = 11;
+  f (__builtin_alloca (n));
+}
Since we can't get any meaningful information from VR_ANTI_RANGE as we 
drill down to a cast, the appropriate thing is to drop it without 
assuming it has a range.  This was as oversight in not handling 
VR_ANTI_RANGE gracefully, and I'll go on a limb here and say that 
attached patch is obvious.

Committed to trunk.
commit 59256dfdee704d08bcd20f0576abd3353f5767cc
Author: Aldy Hernandez <al...@redhat.com>
Date:   Fri Dec 2 04:42:26 2016 -0500

            PR middle-end/78328
            * gimple-ssa-warn-alloca.c (alloca_call_type): Handle
            VR_ANTI_RANGE.

diff --git a/gcc/gimple-ssa-warn-alloca.c b/gcc/gimple-ssa-warn-alloca.c
index e75f2fa..ae379f9 100644
--- a/gcc/gimple-ssa-warn-alloca.c
+++ b/gcc/gimple-ssa-warn-alloca.c
@@ -339,6 +339,8 @@ alloca_call_type (gimple *stmt, bool is_vla, tree 
*invalid_casted_type)
                {
                  // Fall through.
                }
+             else if (range_type == VR_ANTI_RANGE)
+               return alloca_type_and_limit (ALLOCA_UNBOUNDED);
              else if (range_type != VR_VARYING)
                return
                  alloca_type_and_limit (ALLOCA_BOUND_MAYBE_LARGE, max);
diff --git a/gcc/testsuite/gcc.dg/Walloca-12.c 
b/gcc/testsuite/gcc.dg/Walloca-12.c
new file mode 100644
index 0000000..5d71cda
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Walloca-12.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-Walloca-larger-than=128 -O2" } */
+
+void f (void*);
+
+void g (unsigned int n)
+{
+  if (n == 7)
+    n = 11;
+  f (__builtin_alloca (n)); /* { dg-warning "unbounded use of 'alloca'" } */
+}