Index: llvm/docs/LoopTerminology.rst
===================================================================
--- llvm/docs/LoopTerminology.rst
+++ llvm/docs/LoopTerminology.rst
@@ -144,7 +144,19 @@
 Loop Simplify Form
 ==================
 
-TBD
+The Loop Simplify Form is a canonical form that makes
+several analyses and transformations simpler and more effective.
+This loop is ensured by the LoopSimplify (`-loop-simplify`) pass
+and is automatically added by the pass managers when scheduling
+a LoopPass. This pass is implemented in
+`LoopInfo.h http://llvm.org/doxygen/LoopSimplify_8h_source.html`_.
+When it is successful, the loop has:
+
+* A preheader.
+* A single backedge (which implies that there is a single latch).
+* Dedicated exits. That is, no exit block for the loop
+  has a predecessor that is outside the loop. This implies
+  that all exit blocks are dominated by the loop header.
 
 
 Loop Closed SSA (LCSSA)
Index: llvm/include/llvm/Transforms/Utils/LoopSimplify.h
===================================================================
--- llvm/include/llvm/Transforms/Utils/LoopSimplify.h
+++ llvm/include/llvm/Transforms/Utils/LoopSimplify.h
@@ -8,7 +8,8 @@
 //
 // This pass performs several transformations to transform natural loops into a
 // simpler form, which makes subsequent analyses and transformations simpler and
-// more effective.
+// more effective. A summary of this pass is documented in
+// https://llvm.org/docs/LoopTerminology.html#loop-simplify-form
 //
 // Loop pre-header insertion guarantees that there is a single, non-critical
 // entry edge from outside of the loop to the loop header.  This simplifies a