sorry for the noise, forgot to mention ...
Granted, I think that this special "ksub && izZero" case in simplification()
should die and I would be happy to make a PR.
But perhaps you can explain why is it useful or necessary?
Thanks,
On 10/08, Oleg Nesterov wrote:
>
> Hello,
>
> simplification() does
>
> ...
>
> else if (isSigBinOp(sig, &opnum, t1, t2)) {
> BinOp* op = gBinOpTable[opnum];
> Node n1 = t1->node();
> Node n2 = t2->node();
>
> ...
>
> else if (opnum == kSub && isZero(n1))
> return sigBinOp(kMul, sigInt(-1), t2);
>
> and this turns 0-x into -1*x .
>
> To be honest, I don't understand the point, but at least this transformation
> is
> correct. and perhaps C++ compiler will generates the same code with
> -ffast-math.
>
> However, this is inconsistent wrt normalizeAddTerm() which turns -1*x into
> 0-x !
>
> Example:
>
> process(x) = 0-x, -1*x;
>
> C++ code:
>
> for (int i0 = 0; i0 < count; i0 = i0 + 1) {
> float fTemp0 = float(input0[i0]);
> output0[i0] = FAUSTFLOAT(-1.0f * fTemp0); // 0 - x
> output1[i0] = FAUSTFLOAT(0.0f - fTemp0); // -1 * x
> }
>
> looks obviously suboptimal (even if, again, -ffast-math can help).
>
> If I remove the kSub && isZero(n1) "optimization" above I get
>
> for (int i0 = 0; i0 < count; i0 = i0 + 1) {
> float fTemp0 = 0.0f - float(input0[i0]);
> output0[i0] = FAUSTFLOAT(fTemp0);
> output1[i0] = FAUSTFLOAT(fTemp0);
> }
>
> which looks obviously better to me.
>
> -------------------------------------------------------------------------------
>
> And this is one of the reasons (there are more) why the reverted commit
> 428eee11896556707b78f9044d66d2397c9884fa which changed realPropagate()
>
> --- a/compiler/propagate/propagate.cpp
> +++ b/compiler/propagate/propagate.cpp
> @@ -537,7 +537,7 @@ static siglist realPropagate(Tree slotenv, Tree
> path, Tree box, const siglist& l
> Tree exp = outsigs[dst - 1];
> if ((src > 0) & (src <= ins)) {
> // we have a source
> - outsigs[dst - 1] = sigAdd(exp, lsig[src - 1]);
> + outsigs[dst - 1] = simplify(sigAdd(exp,
> lsig[src - 1]));
> }
> }
> }
>
> can make a difference.
>
> Example:
>
> process(x) = -x : route(1,1,1,1);
>
> diff:
>
> - output0[i0] = FAUSTFLOAT(-1.0f * float(input0[i0]));
> + output0[i0] = FAUSTFLOAT(0.0f - float(input0[i0]));
>
> But:
>
> process(x) = -x : route(1,1,1,1) : route(1,1,1,1);
>
> generates the same code again, with or without the commit above.
>
> And of course,
>
> process(x) = -x : route(1,1,1,1) : route(1,1,1,1) : route(1,1,1,1);
>
> leads to the same diff:
>
> - output0[i0] = FAUSTFLOAT(-1.0f * float(input0[i0]));
> + output0[i0] = FAUSTFLOAT(0.0f - float(input0[i0]));
>
> Oleg.
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