unnecessary slow variable is created

[crop2000]

I realized that the following faust dsp creates a unecessary slow variable fSlow0.

import("stdfaust.lib");
volumeM = vslider("volume", 0, -70, +4, 0.1) : ba.db2linear;
process(a) = attach(volumeM:vbargraph("level",0,1));

      virtual void compute(int count, FAUSTFLOAT** RESTRICT inputs, FAUSTFLOAT** RESTRICT outputs) {
		FAUSTFLOAT* input0 = inputs[0];
		FAUSTFLOAT* input1 = inputs[1];
		FAUSTFLOAT* output0 = outputs[0];
		fVbargraph0 = FAUSTFLOAT(std::pow(1e+01f, 0.05f * float(fVslider0)));
		float fSlow0 = fVbargraph0;
		for (int i0 = 0; i0 < count; i0 = i0 + 1) {
			output0[i0] = FAUSTFLOAT(float(input1[i0]));
		}
	}

this becomes relevant if -ec is used because in this case it cannot be simply optimized away.

[crop2000]

this issue can be solved by the following fix:
simplify the code by using occurence:
443fbeb
and don't expand variability if it would happen inside attach in the second arm:
b57237a
the linked commits are part of a PR that introduces also other improvements.