[PR105455] Set edge probabilities when hardening conditionals

[PR105455] Set edge probabilities when hardening conditionals

When turning unconditional edges into conditional, as in
gimple-harden-conditionals.cc:insert_check_and_trap, the newly-created
edge's probability comes out uninitialized, while the previously
unconditional edge's probability is presumably
profile_probability::always.

Mixing initialized and uninitialized probabilities before expand
breaks predict.cc:force_edge_cold: the initialized probability may end
up copied to a REG_BR_PROB note in a conditional branch insn, but if
force_edge_cold is called on that edge, it will find another edge with
uninitialized probability and assume the note is absent.  Later on,
rtl_verify_edges complains that the note does not match the
probability modified by force_edge_cold in the edge.

This patch sets probabilities for edges affected by hardening of
conditionals, both the newly-created edges to trap blocks and the
previously-unconditional edges, so that the former are considered
never taken, while the latter are confirmed as always taken.

for  gcc/ChangeLog

	PR rtl-optimization/105455
	* gimple-harden-conditionals.cc (insert_check_and_trap): Set
	probabilities for newly-conditional edges.

for  gcc/testsuite/ChangeLog

	PR rtl-optimization/105455
	* gcc.dg/pr105455.c: New.