From mboxrd@z Thu Jan  1 00:00:00 1970
From: lehotsky@earthlink.net
To: cgen@sourceware.cygnus.com
Subject: branch-delay slot semantics questions
Date: Fri, 11 May 2001 05:13:00 -0000
Message-id: <200105111205.IAA04658@iron.>
X-SW-Source: 2001-q2/msg00048.html

I found cgen pretty easy to get up and running for the most part.
It's a definitely a handy (and powerful) tool.

But I don't seem to be able to get the instruction in the "delay" slot
to execute.  My branch instructions are all of the form

       (dni "jmp"
         ...
         (delay 1
		(set pc (....)))
         ...  
       )

But my machine seems to suppress the execution of the instruction
in the delay slot, although I don't have any annul code that I'm
aware of...  (when I run the simulator with -ton, the instructions
in the delay slots are never traced.

Anything I should be looking for?  Is there something special my
mloop.in code needs to do?

Is there also any support for dealing with the semantics that
"a branch in the delay-slot is always annulled".  I think I can
implement this by having two bits in the ISA's (setup-semantics (..))
code.  

    (define-isa
      ...
      (setup-semantics (sequence
			 ()
			 (set h-annul-jmp-p h-jump-insn-p)
			 (set h-jump-insn-p (attr BI insn DELAY-SLOT))))
    )

    ; Branch instructions in the shadow of a branch are annulled.  Remember
    ; if last executed instruction was a branch
    (dsh h-annul-jmp-p "remember if last instruction was jump" ()
							       (register BI))
    (dsh h-jump-insn-p "current instruction is a jmp/ret" () (register BI))




And then in every branch instruction, if the h-annul-jmp-p is set,
then we just evaluate the jump as (nop).