[PATCH PR71347][Partial revert r235513]Compute cost for all uses in group

[Bin Cheng]

Hi,
This patch partially reverts part of r235513 to fix PR71347, the original patch is to improve compilation time for a small amount.  Root cause as analyzed in bugzilla PR is that we can't skip computing cost for sub iv_use if it has different position to the first use in group.  The patch also includes a new test.

Bootstrap and test on x86_64.  Is it OK?

Thanks,
bin

2016-05-31  Bin Cheng  <bin.cheng@arm.com>

	PR tree-optimization/71347
	* tree-ssa-loop-ivopts.c (determine_group_iv_cost_address): Compute
	cost for all uses in group.

gcc/testsuite/ChangeLog
2016-05-31  Bin Cheng  <bin.cheng@arm.com>

	PR tree-optimization/71347
	* gcc.dg/tree-ssa/pr71347.c: New test.
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