[LoopInterchange] Preserve LCSSA.

This patch extends LoopInterchange to move LCSSA to the right place
after interchanging. This is required for LoopInterchange to become a
function pass.

An alternative to the manual moving of the PHIs, we could also re-form
the LCSSA phis for a set of interchanged loops, but that's more
expensive.

Reviewers: efriedma, mcrosier, davide

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D52154

llvm-svn: 343132
diff --git a/llvm/test/Transforms/LoopInterchange/interchangeable.ll b/llvm/test/Transforms/LoopInterchange/interchangeable.ll
index 44985d8..a97981c 100644
--- a/llvm/test/Transforms/LoopInterchange/interchangeable.ll
+++ b/llvm/test/Transforms/LoopInterchange/interchangeable.ll
@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt < %s -basicaa -loop-interchange -verify-dom-info -verify-loop-info -verify-scev -S | FileCheck %s
+; RUN: opt < %s -basicaa -loop-interchange -verify-dom-info -verify-loop-info -verify-scev -verify-loop-lcssa -S | FileCheck %s
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"