[Beignet] [PATCH 2/5] GBE: refine longjmp checking.

[Zhigang Gong]

On Thu, Sep 24, 2015 at 07:05:38AM +0000, Yang, Rong R wrote:
> One comment.
> 
> > -----Original Message-----
> > From: Beignet [mailto:beignet-bounces at lists.freedesktop.org] On Behalf Of
> > Zhigang Gong
> > Sent: Monday, September 14, 2015 14:20
> > To: beignet at lists.freedesktop.org
> > Cc: Gong, Zhigang
> > Subject: [Beignet] [PATCH 2/5] GBE: refine longjmp checking.
> > 
> > Signed-off-by: Zhigang Gong <zhigang.gong at intel.com>
> > ---
> >  backend/src/backend/gen_insn_selection.cpp |  2 +-
> >  backend/src/ir/function.hpp                | 17 +++++++++++++++++
> >  2 files changed, 18 insertions(+), 1 deletion(-)
> > 
> > diff --git a/backend/src/backend/gen_insn_selection.cpp
> > b/backend/src/backend/gen_insn_selection.cpp
> > index ab00269..57dbec9 100644
> > --- a/backend/src/backend/gen_insn_selection.cpp
> > +++ b/backend/src/backend/gen_insn_selection.cpp
> > @@ -1154,7 +1154,7 @@ namespace gbe
> >      SelectionInstruction *insn = this->appendInsn(SEL_OP_JMPI, 0, 1);
> >      insn->src(0) = src;
> >      insn->index = index.value();
> > -    insn->extra.longjmp = abs(index - origin) > 800;
> > +    insn->extra.longjmp = ctx.getFunction().getDistance(origin, index)
> > + > 8000;
> >      return insn->extra.longjmp ? 2 : 1;
> >    }
> > 
> > diff --git a/backend/src/ir/function.hpp b/backend/src/ir/function.hpp index
> > b5f4ba2..b924332 100644
> > --- a/backend/src/ir/function.hpp
> > +++ b/backend/src/ir/function.hpp
> > @@ -487,6 +487,23 @@ namespace ir {
> >      Register getSurfaceBaseReg(uint8_t bti) const;
> >      void appendSurface(uint8_t bti, Register reg);
> >      /*! Output the control flow graph to .dot file */
> > +    /*! Get instruction distance between two BBs */
> > +    INLINE uint32_t getDistance(LabelIndex b0, LabelIndex b1) const {
> > +      int start, end;
> > +      if (b0.value() < b1.value()) {
> > +        start = b0.value();
> > +        end = b1.value() - 1;
> > +      } else {
> > +        start = b1.value();
> > +        end = b0.value() - 1;
> > +      }
> > +      uint32_t insnNum = 0;
> > +      for(int i = start; i <= end; i++) {
> > +        BasicBlock &bb = getBlock(LabelIndex(i));
> > +        insnNum += bb.size();
> > +      }
> If front jump, need not include the start and end block's size.
Nice catch, there are more cases than I thought:

Two forward jump cases:

  JMPI created by label instruction:

  b0:
    (      85)  cmp.le(16)   null:UW         g1<8,8,1>:UW    0x1UW           { align1 WE_all 1H switch };
    (      87)  (-f0.any16h) jmpi(1) offset_to_b1                                       { align1 WE_all };
    (      89)  (+f0) if(16) 45                                                 { align1 WE_normal 1H };
    ...


  b1:
     ...

  JMPI created by forward JMPI.

  b0:
    ...
    jmpi(1) offset_to_b1                                       { align1 WE_all };

  b1:
   ...


One backward JMPI only has one case:

b1:


b0:
   ...
   (   11172)  endif(16) 2                     null                            { align1 WE_normal 1H };
   (   11174)  (+f0.any16h) jmpi(1) offset_to_b0                                      { align1 WE_all };

It jumps from b0's end to b1's beginning. So we need to accumulate b1 to b0's instructions.
I did make another mistake in the backward jump case, should not exclude b0.

I will send a new version latter.

BTW, using this solution to determine a long jump is still a hacky work around.
I hope some one could refine the backend to support insert one instruction easily
in code emission stage.

Thanks,
Zhigang Gong.
 
> 
> > +      return insnNum;
> > +    }
> >      void outputCFG();
> >    private:
> >      friend class Context;           //!< Can freely modify a function
> > --
> > 1.9.1
> > 
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