Get stack adjustment from push operand in pushsf splitter

pushsf for -m64/-mx32 looks like

(set (mem:SF (pre_modify:SI (reg/f:SI 7 sp)
			    (plus:SI (reg/f:SI 7 sp)
			    (const_int -8))))
     (reg:SF 22 xmm1 [orig:84 D.1790 ] [84]))

Stack adjustment is in push operand and it isn't stack register mode size
which may be 4 bytes for -mx32.  This patch gets stack adjustment from
push operand if code of push isn't PRE_DEC.

gcc/

	PR target/59929
	* config/i386/i386.md (pushsf splitter): Get stack adjustment
	from push operand if code of push isn't PRE_DEC.

gcc/testsuite/

	PR target/59929
	* gcc.target/i386/pr59929.c: New test.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@207023 138bc75d-0d04-0410-961f-82ee72b054a4