[llvm-commits] [llvm] r142731 - in /llvm/trunk: lib/Analysis/ScalarEvolution.cpp test/Analysis/ScalarEvolution/load.ll

[Nick Lewycky]

On 23 October 2011 07:15, Duncan Sands <baldrick at free.fr> wrote:

> Hi Nick,
>
> > -  if (const CmpInst *CI = dyn_cast<CmpInst>(I))
> > +  if (CmpInst *CI = dyn_cast<CmpInst>(I))
> >       return ConstantFoldCompareInstOperands(CI->getPredicate(),
> Operands[0],
> >                                              Operands[1], TD);
> > +  if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
> > +    if (!LI->isVolatile())
> > +      return ConstantFoldLoadFromConstPtr(Operands[0], TD);
> > +  }
> >     return ConstantFoldInstOperands(I->getOpcode(), I->getType(),
> Operands, TD);
>
> maybe you could use instsimplify here?  It does constant folding and more
> besides.  It can break LCSSA form, so y so,
> check out the loop transform users of instsimplify to seou may need to
> check for that (ife how).


As far as I can see, LCSSA isn't documented and I don't understand it well
enough to know whether I'm preserving it or breaking it etc. I know it
involves creating 1-operand PHI nodes in strategic places and that's about
it.

Are there cases where InstructionSimplify will return a Constant that the
constant folder won't? This code is entirely based off of a mapping to
Constant*, so instsimplify won't help without more refactoring.

That refactoring would be scary because while we can represent the arbitrary
values, we'll find ourselves effectively unrolling the loop as we build up a
larger and larger SCEV expression. I'd like to leave unrolling to the
unrolling pass.

Nick

> @@ -4993,7 +5109,10 @@
> >             if (const CmpInst *CI = dyn_cast<CmpInst>(I))
> >               C = ConstantFoldCompareInstOperands(CI->getPredicate(),
> >                                                   Operands[0],
> Operands[1], TD);
> > -          else
> > +          else if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
> > +            if (!LI->isVolatile())
> > +              C = ConstantFoldLoadFromConstPtr(Operands[0], TD);
> > +          } else
> >               C = ConstantFoldInstOperands(I->getOpcode(), I->getType(),
> >                                            Operands, TD);
> >             if (!C) return V;
>
> Likewise.
>
> Ciao, Duncan.
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