[LoopVersioning] Require loop-simplify form for loop versioning.

Summary:
Requiring loop-simplify form for loop versioning ensures that the
runtime check block always dominates the exit block.
    
This patch closes #30958 (https://llvm.org/bugs/show_bug.cgi?id=30958).

Reviewers: silviu.baranga, hfinkel, anemet, ashutosh.nema

Subscribers: ashutosh.nema, mzolotukhin, efriedma, hfinkel, llvm-commits

Differential Revision: https://reviews.llvm.org/D27469

llvm-svn: 290116

4 files changed, 17 insertions, 14 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopDistribute.cpp b/llvm/lib/Transforms/Scalar/LoopDistribute.cpp
index 1db8caa0a34..1da0fd8d2a8 100644
--- a/llvm/lib/Transforms/Scalar/LoopDistribute.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopDistribute.cpp
@@ -606,11 +606,13 @@ public:
     DEBUG(dbgs() << "\nLDist: In \"" << L->getHeader()->getParent()->getName()
                  << "\" checking " << *L << "\n");
 
-    BasicBlock *PH = L->getLoopPreheader();
-    if (!PH)
-      return fail("NoHeader", "no preheader");
     if (!L->getExitBlock())
       return fail("MultipleExitBlocks", "multiple exit blocks");
+    if (!L->isLoopSimplifyForm())
+      return fail("NotLoopSimplifyForm",
+                  "loop is not in loop-simplify form");
+
+    BasicBlock *PH = L->getLoopPreheader();
 
     // LAA will check that we only have a single exiting block.
     LAI = &GetLAA(*L);
diff --git a/llvm/lib/Transforms/Scalar/LoopLoadElimination.cpp b/llvm/lib/Transforms/Scalar/LoopLoadElimination.cpp
index 8e83c4700aa..08e7acdaaf7 100644
--- a/llvm/lib/Transforms/Scalar/LoopLoadElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopLoadElimination.cpp
@@ -517,6 +517,11 @@ public:
         return false;
       }
 
+      if (!L->isLoopSimplifyForm()) {
+        DEBUG(dbgs() << "Loop is not is loop-simplify form");
+        return false;
+      }
+
       // Point of no-return, start the transformation.  First, version the loop
       // if necessary.
 
diff --git a/llvm/lib/Transforms/Scalar/LoopVersioningLICM.cpp b/llvm/lib/Transforms/Scalar/LoopVersioningLICM.cpp
index aa09f894310..c23d891b650 100644
--- a/llvm/lib/Transforms/Scalar/LoopVersioningLICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopVersioningLICM.cpp
@@ -218,9 +218,10 @@ private:
 
 /// \brief Check loop structure and confirms it's good for LoopVersioningLICM.
 bool LoopVersioningLICM::legalLoopStructure() {
-  // Loop must have a preheader, if not return false.
-  if (!CurLoop->getLoopPreheader()) {
-    DEBUG(dbgs() << "    loop preheader is missing\n");
+  // Loop must be in loop simplify form.
+  if (!CurLoop->isLoopSimplifyForm()) {
+    DEBUG(
+        dbgs() << "    loop is not in loop-simplify form.\n");
     return false;
   }
   // Loop should be innermost loop, if not return false.
@@ -256,11 +257,6 @@ bool LoopVersioningLICM::legalLoopStructure() {
     DEBUG(dbgs() << "    loop depth is more then threshold\n");
     return false;
   }
-  // Loop should have a dedicated exit block, if not return false.
-  if (!CurLoop->hasDedicatedExits()) {
-    DEBUG(dbgs() << "    loop does not has dedicated exit blocks\n");
-    return false;
-  }
   // We need to be able to compute the loop trip count in order
   // to generate the bound checks.
   const SCEV *ExitCount = SE->getBackedgeTakenCount(CurLoop);
diff --git a/llvm/lib/Transforms/Utils/LoopVersioning.cpp b/llvm/lib/Transforms/Utils/LoopVersioning.cpp
index b3c61691da3..29756d9dab7 100644
--- a/llvm/lib/Transforms/Utils/LoopVersioning.cpp
+++ b/llvm/lib/Transforms/Utils/LoopVersioning.cpp
@@ -36,7 +36,7 @@ LoopVersioning::LoopVersioning(const LoopAccessInfo &LAI, Loop *L, LoopInfo *LI,
     : VersionedLoop(L), NonVersionedLoop(nullptr), LAI(LAI), LI(LI), DT(DT),
       SE(SE) {
   assert(L->getExitBlock() && "No single exit block");
-  assert(L->getLoopPreheader() && "No preheader");
+  assert(L->isLoopSimplifyForm() && "Loop is not in loop-simplify form");
   if (UseLAIChecks) {
     setAliasChecks(LAI.getRuntimePointerChecking()->getChecks());
     setSCEVChecks(LAI.getPSE().getUnionPredicate());
@@ -278,8 +278,8 @@ public:
     bool Changed = false;
     for (Loop *L : Worklist) {
       const LoopAccessInfo &LAI = LAA->getInfo(L);
-      if (LAI.getNumRuntimePointerChecks() ||
-          !LAI.getPSE().getUnionPredicate().isAlwaysTrue()) {
+      if (L->isLoopSimplifyForm() && (LAI.getNumRuntimePointerChecks() ||
+          !LAI.getPSE().getUnionPredicate().isAlwaysTrue())) {
         LoopVersioning LVer(LAI, L, LI, DT, SE);
         LVer.versionLoop();
         LVer.annotateLoopWithNoAlias();