tree-inline: Fix a -fcompare-debug issue in the inliner [PR94167]

tree-inline: Fix a -fcompare-debug issue in the inliner [PR94167]

The following testcase fails with -fcompare-debug.  The problem is that
bar is marked as address_taken only with -g and not without.
I've tracked it down to insert_init_stmt calling gimple_regimplify_operands
even on DEBUG_STMTs.  That function will just insert normal stmts before
the DEBUG_STMT if the DEBUG_STMT operand isn't gimple val or invariant.
While DCE will turn those statements into debug temporaries, it can cause
differences in SSA_NAMEs and more importantly, the ipa references are
generated from those before the DCE happens.
On the testcase, the DEBUG_STMT value is (int)bar.

We could generate DEBUG_STMTs with debug temporaries instead, but I fail to
see the reason to do that, DEBUG_STMTs allow other expressions and all we
want to ensure is that the expressions aren't too large (arbitrarily
complex), but during inlining/function versioning I don't see why something
would queue a DEBUG_STMT with arbitrarily complex expressions in there.

2020-03-16  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/94166
	* tree-ssa-reassoc.c (sort_by_mach_mode): Use SSA_NAME_VERSION
	as secondary comparison key.

	* gcc.dg/pr94166.c: New test.