sel-sched: Verify change before replacing dest in EXPR_INSN_RTX [PR112995]

sel-sched: Verify change before replacing dest in EXPR_INSN_RTX [PR112995]

PR112995 exposed one issue in current try_replace_dest_reg
that the result rtx insn after replace_dest_with_reg_in_expr
is probably unable to match any constraints.  Although there
are some checks on the changes onto dest or src of orig_insn,
none is performed on the EXPR_INSN_RTX.

Initially we have:

(insn 31 6 10 2 (set (reg/v:SI 9 9 [orig:119 c ] [119])
                     (reg/v:SI 64 0 [orig:119 c ] [119]))
                "test.i":5:5 555 {*movsi_internal1} ... )
...
(insn 25 10 27 2 (set (reg:DI 64 0 [135])
                      (sign_extend:DI
                         (reg/v:SI 9 9 [orig:119 c ] [119])))
                 "test.i":6:5 31 {extendsidi2} ...)

with moving up, we have:

(insn 46 0 0 (set (reg:DI 64 0 [135])
                  (sign_extend:DI
                      (reg/v:SI 64 0 [orig:119 c ] [119])))
                   31 {extendsidi2} ...)

in try_replace_dest_reg, we updated the above EXPR_INSN_RTX to:

(insn 48 0 0 (set (reg:DI 32 0)
                  (sign_extend:DI
                      (reg/v:SI 64 0 [orig:119 c ] [119])))
                   31 {extendsidi2} ...)

The dest (reg 64) is a VR (also VSX REG), the updating makes
it become to (reg 32) which is a FPR (also VSX REG), we have
an alternative to match "VR,VR" but no one to match "FPR/VSX,
VR/VSX", so it fails with ICE.

This patch is to add the check before actually replacing dest
in expr with reg.

	PR rtl-optimization/112995

gcc/ChangeLog:

	* sel-sched.cc (try_replace_dest_reg): Check the validity of the
	replaced insn before actually replacing dest in expr.

gcc/testsuite/ChangeLog:

	* gcc.target/powerpc/pr112995.c: New test.