Why is this reordering of sub and mul instructions helpful?

This is an example code from Computer Systems: A Programmer's Perspective.

short foo(short a, short b) {    short result;    result = b;    while(b > 0) {        result *= a;        b -= a;    }    return result;}

Compiling this with gcc14.2 using -O1 and -O3 gives the following assembly (godbolt)

O1

foo:        movl    %esi, %eax        movl    %esi, %ecx        testw   %si, %si        jle     .L1.L3:        imull   %edi, %eax        subl    %edi, %ecx        testw   %cx, %cx        jg      .L3.L1:        ret

O3

foo:        movl    %esi, %eax        movl    %esi, %edx        testw   %si, %si        jle     .L1.L3:        subl    %edi, %edx        imull   %edi, %eax        testw   %dx, %dx        jg      .L3.L1:        ret

With O3, sub comes before imul - why is this reordering helpful?

1. I am assuming this has to do with instruction-level parallelism, but cannot get the exact reason. Is it that performing subtraction first will allow parts of multiplication to also get done with some idle ALUs?
2. With respect to pipelining, is there any difference due to this reordering?