Paolo asked for GCC to allow deduction of auto from a variable-length
array. Since auto doesn't have the issues involved with normal template
deduction from VLAs (namely, the type not being link-time constant),
this seems reasonable to me.
Tested x86_64-pc-linux-gnu, applying to trunk.
commit 002b9c9ad8b14999fa87c65f3ccdce772086edd8
Author: Jason Merrill <ja...@redhat.com>
Date: Thu Aug 4 11:48:40 2011 -0400
* pt.c (unify) [TEMPLATE_TYPE_PARM]: Allow VLA for C++0x 'auto'.
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 571da6d..10fdced 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -15932,10 +15932,11 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
that were talking about variable-sized arrays (like
`int[n]'), rather than arrays of unknown size (like
`int[]').) We'll get very confused by such a type since
- the bound of the array will not be computable in an
- instantiation. Besides, such types are not allowed in
- ISO C++, so we can do as we please here. */
- if (variably_modified_type_p (arg, NULL_TREE))
+ the bound of the array is not constant, and therefore
+ not mangleable. Besides, such types are not allowed in
+ ISO C++, so we can do as we please here. We do allow
+ them for 'auto' deduction, since that isn't ABI-exposed. */
+ if (!is_auto (parm) && variably_modified_type_p (arg, NULL_TREE))
return unify_vla_arg (explain_p, arg);
/* Strip typedefs as in convert_template_argument. */
diff --git a/gcc/testsuite/g++.dg/ext/vla11.C b/gcc/testsuite/g++.dg/ext/vla11.C
new file mode 100644
index 0000000..8f3be9e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/vla11.C
@@ -0,0 +1,8 @@
+// Test that auto works with VLAs.
+// { dg-options -std=c++0x }
+
+void bar(int n)
+{
+ float loc2[n];
+ auto&& range = loc2;
+}
