[PATCH GCC]Allow cfgcleanup to remove forwarder loop preheaders and latches

[bin.cheng]

Hi,
This patch is to fix regression reported in PR60280 by removing forward loop
headers/latches in cfg cleanup if possible.  Several tests are broken by
this change since cfg cleanup is shared by all optimizers.  Some tests has
already been fixed by recent patches, I went through and fixed the others.
One case needs to be clarified is "gcc.dg/tree-prof/update-loopch.c".  When
GCC removing a basic block, it checks profile information by calling
check_bb_profile after redirecting incoming edges of the bb.  This certainly
results in warnings about invalid profile information and causes the case to
fail.  I will send a patch to skip checking profile information for a
removing basic block in stage 1 if it sounds reasonable.  For now I just
twisted the case itself.

Bootstrap and tested on x86_64 and arm_a15.

Is it OK?


2014-02-25  Bin Cheng  <bin.cheng@arm.com>

	PR target/60280
	* tree-cfgcleanup.c (tree_forwarder_block_p): Protect loop
	preheaders and latches only if requested.  Fix latch if it
	is removed.
	* tree-ssa-dom.c (tree_ssa_dominator_optimize): Set
	LOOPS_HAVE_PREHEADERS.

gcc/testsuite/ChangeLog
2014-02-25  Bin Cheng  <bin.cheng@arm.com>

	PR target/60280
	* gnat.dg/renaming5.adb: Change to two expected gotos.
	* gcc.dg/tree-ssa/pr21559.c: Change back to three expected
	jump threads.
	* gcc.dg/tree-prof/update-loopch.c: Check two "Invalid sum"
	messages for removed basic block.
	* gcc.dg/tree-ssa/ivopt_1.c: Fix unreliable scanning string.
	* gcc.dg/tree-ssa/ivopt_2.c: Ditto.
	* gcc.dg/tree-ssa/ivopt_3.c: Ditto.
	* gcc.dg/tree-ssa/ivopt_4.c: Ditto.
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