🚀 go-pugleaf

Consider the following simple program which returns the position of the first '1'
bit in an integer (in this case should return 2). 

int main()
{
	register int x = 4;
	int i;

	for(i=0; i<8 && ((x&1) == 0); x >>= 1, i++) 
		;
	return(i);
}

When compiled by "gcc -v -O -S gcctest.c", the following results:
gcc version 1.40
 /usr/local/lib/gcc-cpp -v -undef -D__GNUC__ -Dmc68k -Dunix -Dunixpc -D__mc68k__ -D__unix__ -D__unixpc__ -D__OPTIMIZE__ gcctest.c /usr/tmp/cca24532.cpp
GNU CPP version 1.40
 /usr/local/lib/gcc-cc1 /usr/tmp/cca24532.cpp -quiet -dumpbase gcctest.c -O -version -o gcctest.s
GNU C version 1.40 (68k, AT&T UnixPC/gas) compiled by GNU C version 1.40.
default target switches:
	.file	"gcctest.c"
gcc_compiled.:
.text
	.even
.globl _main
_main:
	link a6,#0
	movel d2,sp@-
	moveq #4,d1
	moveq #0,d0
L5:
	btst #0,d1
	jne L3
	asrl #1,d1
	addql #1,d0
	moveq #7,d2
	cmpl d0,d2
	jge L5
L3:
	movel a6@(-4),d2
	unlk a6
	rts

This works as expected (return value 2).  However, when the -fstrength-reduce flag is added, we get:
gcc version 1.40
 /usr/local/lib/gcc-cpp -v -undef -D__GNUC__ -Dmc68k -Dunix -Dunixpc -D__mc68k__ -D__unix__ -D__unixpc__ -D__OPTIMIZE__ gcctest.c /usr/tmp/cca24537.cpp
GNU CPP version 1.40
 /usr/local/lib/gcc-cc1 /usr/tmp/cca24537.cpp -quiet -dumpbase gcctest.c -fstrength-reduce -O -version -o gcctest.s
GNU C version 1.40 (68k, AT&T UnixPC/gas) compiled by GNU C version 1.40.
default target switches:
	.file	"gcctest.c"
gcc_compiled.:
.text
	.even
.globl _main
_main:
	link a6,#0
	moveq #4,d1
	moveq #7,d0
L5:
	btst #0,d1
	jne L3
	asrl #1,d1
	dbra d0,L5
	clrw d0
	subql #1,d0
	jcc L5
	moveq #8,d0
L3:
	unlk a6
	rts

This does not work properly (it returns 5, rather than 2).

Other compilation options (e.g. -fcombine-regs) do not appear to alter this behavior.
I've not had any other problems with -fstrength-reduce, but it clearly causes major
problems with the above code fragment (simplified from a real program).