diff --git a/llvm/lib/Transforms/Vectorize/VPlan.h b/llvm/lib/Transforms/Vectorize/VPlan.h
--- a/llvm/lib/Transforms/Vectorize/VPlan.h
+++ b/llvm/lib/Transforms/Vectorize/VPlan.h
@@ -1129,6 +1129,23 @@
 /// phis for first order recurrences, pointer inductions and reductions. The
 /// start value is the first operand of the recipe and the incoming value from
 /// the backedge is the second operand.
+///
+/// Inductions are modeled using the following sub-classes:
+///  * VPCanonicalIVPHIRecipe: Canonical scalar induction of the vector loop,
+///    starting at a specified value (zero for the main vector loop, the resume
+///    value for the epilogue vector loop) and stepping by 1. The induction
+///    controls exiting of the vector loop by comparing against the vector trip
+///    count. Produces a scalar PHI for the induction value per iteration.
+///  * VPWidenIntOrFpInductionRecipe: Generates vector values for integer and
+///    floating point inductions with arbitrary start and step values. Produces
+///    vector phis for each part.
+///  * VPDerivedIVRecipe: Converts the canonical IV value to the corresponding
+///  value of an IV with different start and step values.
+///  * VPScalarIVStepsRecipe: Generates per-lane scalar values based on a
+///  canonical or derived induction.
+///  * VPWidenPointerInductionRecipe: Generate vector and scalar values for a
+///    pointer induction. Produces either vector phis or scalar values based on
+///    the canonical induction.
 class VPHeaderPHIRecipe : public VPRecipeBase, public VPValue {
 protected:
   VPHeaderPHIRecipe(unsigned char VPVID, unsigned char VPDefID, PHINode *Phi,