[Ada] Fix gnat.dg/return3.adb regression

[Eric Botcazou]

The problem is that the new call to cleanup_cfg in gimple_expand_cfg has 
short-circuited the machinery that emits nops to carry goto locus at -O0.
The machinery works in CFGLAYOUT mode, but here we're still in CFGRTL.

The attached patch makes it so that forwarder blocks are not deleted by 
try_optimize_cfg if CLEANUP_NO_INSN_DEL and partially extends the above 
machinery to the CFGRTL mode.

Bootstrapped/regtested on x86_64-suse-linux, applied on the mainline.


2012-05-26  Eric Botcazou  <ebotcazou@adacore.com>

	* cfgcleanup.c (try_optimize_cfg): Do not delete forwarder blocks
	if CLEANUP_NO_INSN_DEL.
	* cfgrtl.c (unique_locus_on_edge_between_p): New function extracted
	from cfg_layout_merge_blocks.
	(emit_nop_for_unique_locus_between): New function.
	(rtl_merge_blocks): Invoke emit_nop_for_unique_locus_between.
	(cfg_layout_merge_blocks): Likewise.


-- 
Eric Botcazou
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