[cedet-semantic] Detecting CPU stalls with semantic

[<myr...@us...>]

Hi,

I'm working on a mode to edit vector processing unit (vpu) code in
emacs and was asked for stall detection.  Aparently this exist in some
tool for pro ps2 developers.

The VPU has 2 parallel execution units so each line (cycle) has 2
instructions, one called "upper" and the next "lower" and would
typically look like this:

  MULq.xyz      VF14, VF14, Q	MR32.xy       VF08, VF08

Here, "MULq" is the upper instruction, and "MR32" is the lower.  (But
this is not really important).

Now, since MUL has throughput/latency of 1/4, I can use MUL
instruction in the next line (cycle) ((latency 1)), but I can't read
the VF14 register until 4 lines later ((throughput 4)) or the cpu will
stall (and hence do nothing I could use it for in the meantime); like
so:

  MAX.xyw       VF27, VF27, VF14	MR32.x        VF02, VF01

To confuse the issue, not all instructions have the same
throughput/latency nor do they always use the same execution unit.
The DIV (lower instruction) for example is 7/7 so I can't use a DIV,
SQRT or RSQRT instructions for 7 lines (without stalls), but I can use
other lower instructions during this time.

So, can semantic provide me with some information to detect stalls, or
do I have to code some Real Magic(tm) to do this?  How to actually
display the stall info is a different story.


Johann

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