Locating where first param of an invoke gets put on the stack

I want to thank everyone who worked on asm, such a wonderful framework. I
wish I had found it earlier, it would have saved me so much time. I have a
bad habit of reinventing the wheel when I need something, trying to avoid
that here if possible. Really hoping ASM contains some feature that could
make this easier.

I'd like to inject some code prior to the first param of an invoke* is put
on the stack. My problem here is locating when the first param (or "sub
param" enters the stack);

If it is something like

Log.print("hello","world");
---
 ldc           #29                 // String TAG
 ldc           #31                 // String MSG
15: invokestatic  #37                 // Method
logg/loggl/Log.print:(Ljava/lang/String;Ljava/lang/String;)I

it is fairly simple, I can just move back two positions and be in front of
the ldc "TAG", and then inject my code.


But when something like this happens it gets complicated , dosomething
takes 7 ints. I need to jump to right before the bipush 100, so I can't
simply move back 7 positions.

 int i = 100;
 dosomething(x(32,i/2),1,20 * 2,1,1,81,1);
---
bipush        100
istore_2
bipush        32
iload_2
iconst_2
idiv
invokestatic  #6                  // Method x:(II)I
iconst_1
bipush        40
iconst_1
iconst_1
bipush        81
iconst_1
invokestatic  #7                  // Method
dosomething:(IIIIIII)Ljava/lang/String;

So, does ASM hold any magic for me here? Something easier than just keeping
track of the effects of each instruction on the stack, and walking
backwards?

Thank You,
Jon


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