Eliminate more token factors by taking advantage of transitivity:

if TF depends on A and B, and A depends on B, TF just needs to depend on
A.  With Jim's alias-analysis stuff enabled, this compiles the testcase in
PR892 into:

__Z4test3Val:
        subl $44, %esp
        call L__Z3foov$stub
        movl %edx, 28(%esp)
        movl %eax, 32(%esp)
        movl %eax, 24(%esp)
        movl %edx, 36(%esp)
        movl 52(%esp), %ecx
        movl %ecx, 4(%esp)
        movl %eax, 8(%esp)
        movl %edx, 12(%esp)
        movl 48(%esp), %eax
        movl %eax, (%esp)
        call L__Z3bar3ValS_$stub
        addl $44, %esp
        ret

instead of:

__Z4test3Val:
        subl $44, %esp
        call L__Z3foov$stub
        movl %eax, 24(%esp)
        movl %edx, 28(%esp)
        movl 24(%esp), %eax
        movl %eax, 32(%esp)
        movl 28(%esp), %eax
        movl %eax, 36(%esp)
        movl 32(%esp), %eax
        movl 36(%esp), %ecx
        movl 52(%esp), %edx
        movl %edx, 4(%esp)
        movl %eax, 8(%esp)
        movl %ecx, 12(%esp)
        movl 48(%esp), %eax
        movl %eax, (%esp)
        call L__Z3bar3ValS_$stub
        addl $44, %esp
        ret

llvm-svn: 30821