Fix ICE due to "combine" creating unreachable EH blocks (PR target/88861)

Fix ICE due to "combine" creating unreachable EH blocks (PR target/88861)

PR target/88861 reports an ICE in "ce2" due to an unreachable
basic block.

The block becomes unreachable in "combine" when delete_noop_moves
deletes an insn with a REG_EH_REGION, deleting the EH edge, the
only edge leading to the basic block.

Normally, rest_of_handle_combine would call cleanup_cfg, deleting
unreachable blocks, if combine_instructions returns true, and
combine_instructions does return true for some cases of edge-removal,
but it doesn't for this case, leading to the ICE.

This patch updates delete_noop_moves so that it returns true if
it deletes any edges, and passes that through to combine_instructions,
so that it too will return true if any edges were deleted, ensuring that
cleanup_cfg will be called by rest_of_handle_combine for this case,
deleting the now-unreachable block, and fixing the ICE.

gcc/ChangeLog:
	PR target/88861
	* combine.c (delete_noop_moves): Convert to "bool" return,
	returning true if any edges are eliminated.
	(combine_instructions): Also return true if delete_noop_moves
	returns true.

gcc/testsuite/ChangeLog:
	PR target/88861
	* g++.dg/torture/pr88861.C: New test.

From-SVN: r267984