  A search for CP violation in the phase space of the decay
$D^+\to\pi^-\pi^+\pi^+$ is reported using $pp$ collision data, corresponding to
an integrated luminosity of 1.0 fb$^{-1}$, collected by the LHCb experiment at
a centre-of-mass energy of 7 TeV. The Dalitz plot distributions for $3.1\times
10^6$ $D^+$ and $D^-$ candidates are compared with binned and unbinned
model-independent techniques. No evidence for CP violation is found.
