Steven,
In the MD file, I have this pattern:
(define_insn "setallocate"
[(setallocate (match_operand:DI 0 "general_operand" "r")
)]
""
"allocate %0\t\t#TCB_INSTRUCTIONS"
[(set_attr "type" "multi")])
As you said dce takes out the instruction when flag -01 is engaged. I
would like to reformat the pattern with the proper side-effects to
ensure that the instruction will stay whatever flag is used. Any clue in
this example ? I have tried unspec_volatile without success though. As
follow,
(define_insn "setallocate"
[(setallocate
(unspec_volatile:DI [ (match_operand:DI 0 "general_operand"
"r")]
UNSPEC_ALLOCATE)
)]
""
"allocate %0\t\t#TCB_INSTRUCTIONS"
[(set_attr "type" "multi")])
Thanks for any help.
Thomas
Steven Bosscher wrote:
On Thu, Sep 11, 2008 at 10:38 AM, Thomas A.M. Bernard <[EMAIL PROTECTED]> wrote:
Hi,
I inserted some extra instructions in the Alpha back-end (MD files). They
are properly emitted when the flag -O0 is enabled. Since they have no side
effects and no dependencies on other instructions, they are omitted when
flag -O1 is engaged. Is there a way (I mean attribute/constraint in their MD
patterns) to avoid that and keep the extra instructions in any case ?
Depends on how you modeled your instructions. You could use
unspec_volatile, but if you modeled "normal" instructions, you have to
somehow make the side-effects of your instructions clear. Otherwise,
dead code elimination will just remove the instructions (no
dependencies -> dead).
But you'd have to show what you're doing and what you're trying to
achieve, exactly, for a more helpful answer ;-)
Gr.
Steven
