Fix ICE on loop over constant vector at -O

[Eric Botcazou]

This is an internal error in for_each_index at -O:

+===========================GNAT BUG DETECTED==============================+
| 4.8.0 20121208 (experimental) [trunk revision 194319] (x86_64-suse-linux) 
GCC error:|
| in for_each_index, at tree-ssa-loop-im.c:324                             |
| Error detected around vect9.adb:45:1|

The callback is invoked on a vector CONST_DECL and stops.  That's an unusual 
situation (the CONST_DECL is wrapped up in a VIEW_CONVERT_EXPR to array type) 
but IMO there is no reason to accept other DECLs and stop on CONST_DECLs.

Tested on x86_64-suse-linux, applied on the mainline as obvious.


2012-12-08  Eric Botcazou  <ebotcazou@adacore.com>

	* tree-ssa-loop-im.c (for_each_index) <CONST_DECL>: New case.


2012-12-08  Eric Botcazou  <ebotcazou@adacore.com>

	* gnat.dg/vect9.ad[sb]: New test.
	* gnat.dg/vect9_pkg.ads: New helper.


-- 
Eric Botcazou
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