[PATCH] Fix bug in scheduler's handling of DEBUG_INSNs

[Maxim Kuvyrkov <maxim at codesourcery dot com>]

This patch fixes an ICE in sched-deps.c due to a dereference of an empty list.

The problem is in handling of DEBUG_INSNs and its peculiarity of disregarding requests to free dependence lists in certain cases.  This patch fixes up an instance of disregarding such a request going wrong.  Along the way the patch simplifies add_dependence_list_and_free to an equivalent, but simpler, code.

[Rant: I consider this peculiarity of handling DEBUG_INSNs in sched-deps to be a hack and think that DEBUG_INSNs should be handled differently by creating a new type of dependencies.  On the other hand, I understand that such a change is not trivial to implement and that the current implementation has a great argument for it -- that it works.]

Tested on mips-linux-gnu with no regressions.  OK to apply?

Thank you,

--
Maxim Kuvyrkov
CodeSourcery / Mentor Graphics

Attachment: sched-deps-fix.ChangeLog
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Attachment: sched-deps-fix.patch
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