[LoopInterchange] Preserve ScalarEvolution, by forgetting about interchanged loops.

[fhahn]

Summary

As preparation for LoopInterchange becoming a loop pass, it needs to
preserve ScalarEvolution. Even though interchanging should not change
the trip count of the loop, it modifies loop entry, latch and exit
blocks.

I added -verify-scev to some loop interchange tests, but the verification does
not catch problems caused by missing invalidation of SE in loop interchange, as
the trip counts themselves do not change. So there might be potential to
make the SE verification covering more stuff in the future.

[efriedma]

LGTM

llvm/trunk/lib/Transforms/Scalar/LoopInterchange.cpp

void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<LoopInfoWrapperPass>();
     AU.addRequired<DependenceAnalysisWrapperPass>();
     AU.addRequiredID(LoopSimplifyID);
     AU.addRequiredID(LCSSAID);
     AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
 
     AU.addPreserved<DominatorTreeWrapperPass>();
     AU.addPreserved<LoopInfoWrapperPass>();
+    AU.addPreserved<ScalarEvolutionWrapperPass>();
   }
 
   bool runOnFunction(Function &F) override {
     if (skipFunction(F))
       return false;
 
     SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
     LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
for (BasicBlock *BB : OrigInnerBBs) {
     else
       LI->changeLoopFor(BB, NewInner);
   }
 
   // The preheader of the original outer loop becomes part of the new
   // outer loop.
   NewOuter->addBlockEntry(OrigOuterPreHeader);
   LI->changeLoopFor(OrigOuterPreHeader, NewOuter);
+
+  // Tell SE that we move the loops around.
+  SE->forgetLoop(NewOuter);
+  SE->forgetLoop(NewInner);
 }
 
 bool LoopInterchangeTransform::transform() {
   bool Transformed = false;
   Instruction *InnerIndexVar;
 
   if (InnerLoop->getSubLoops().empty()) {
     BasicBlock *InnerLoopPreHeader = InnerLoop->getLoopPreheader();

llvm/trunk/test/Transforms/LoopInterchange/interchangeable.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt < %s -basicaa -loop-interchange -verify-dom-info -verify-loop-info -S | FileCheck %s
+; RUN: opt < %s -basicaa -loop-interchange -verify-dom-info -verify-loop-info -verify-scev -S | FileCheck %s
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 @A = common global [100 x [100 x i64]] zeroinitializer
 @B = common global [100 x i64] zeroinitializer
 
 ;;  for(int i=0;i<100;i++)

llvm/trunk/test/Transforms/LoopInterchange/phi-ordering.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt < %s -loop-interchange -verify-dom-info -verify-loop-info -S 2>&1 | FileCheck %s
+; RUN: opt < %s -loop-interchange -verify-dom-info -verify-loop-info -verify-scev -S 2>&1 | FileCheck %s
 ;; Checks the order of the inner phi nodes does not cause havoc.
 ;; The inner loop has a reduction into c. The IV is not the first phi.
 
 target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
 target triple = "armv8--linux-gnueabihf"