7 files changed, 100 insertions, 8 deletions
diff --git a/llvm/include/llvm/Transforms/Utils/LoopSimplify.h b/llvm/include/llvm/Transforms/Utils/LoopSimplify.h
new file mode 100644
index 00000000000..7cf89eaeb93
--- /dev/null
+++ b/llvm/include/llvm/Transforms/Utils/LoopSimplify.h
@@ -0,0 +1,65 @@
+//===- LoopSimplify.h - Loop Canonicalization Pass --------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass performs several transformations to transform natural loops into a
+// simpler form, which makes subsequent analyses and transformations simpler and
+// more effective.
+//
+// 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
+// number of analyses and transformations, such as LICM.
+//
+// Loop exit-block insertion guarantees that all exit blocks from the loop
+// (blocks which are outside of the loop that have predecessors inside of the
+// loop) only have predecessors from inside of the loop (and are thus dominated
+// by the loop header).  This simplifies transformations such as store-sinking
+// that are built into LICM.
+//
+// This pass also guarantees that loops will have exactly one backedge.
+//
+// Indirectbr instructions introduce several complications. If the loop
+// contains or is entered by an indirectbr instruction, it may not be possible
+// to transform the loop and make these guarantees. Client code should check
+// that these conditions are true before relying on them.
+//
+// Note that the simplifycfg pass will clean up blocks which are split out but
+// end up being unnecessary, so usage of this pass should not pessimize
+// generated code.
+//
+// This pass obviously modifies the CFG, but updates loop information and
+// dominator information.
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_TRANSFORMS_UTILS_LOOPSIMPLIFY_H
+#define LLVM_TRANSFORMS_UTILS_LOOPSIMPLIFY_H
+
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/PassManager.h"
+
+namespace llvm {
+
+/// This pass is responsible for loop canonicalization.
+class LoopSimplifyPass : public PassInfoMixin<LoopSimplifyPass> {
+public:
+  PreservedAnalyses run(Function &F, AnalysisManager<Function> &AM);
+};
+
+/// \brief Simplify each loop in a loop nest recursively.
+///
+/// This takes a potentially un-simplified loop L (and its children) and turns
+/// it into a simplified loop nest with preheaders and single backedges. It will
+/// update \c AliasAnalysis and \c ScalarEvolution analyses if they're non-null.
+bool simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, ScalarEvolution *SE,
+                  AssumptionCache *AC, bool PreserveLCSSA);
+
+} // end namespace llvm
+
+#endif // LLVM_TRANSFORMS_UTILS_LOOPSIMPLIFY_H
diff --git a/llvm/include/llvm/Transforms/Utils/LoopUtils.h b/llvm/include/llvm/Transforms/Utils/LoopUtils.h
index 863fc2076d5..d9e9e0143ca 100644
--- a/llvm/include/llvm/Transforms/Utils/LoopUtils.h
+++ b/llvm/include/llvm/Transforms/Utils/LoopUtils.h
@@ -323,14 +323,6 @@ private:
 BasicBlock *InsertPreheaderForLoop(Loop *L, DominatorTree *DT, LoopInfo *LI,
                                    bool PreserveLCSSA);
 
-/// \brief Simplify each loop in a loop nest recursively.
-///
-/// This takes a potentially un-simplified loop L (and its children) and turns
-/// it into a simplified loop nest with preheaders and single backedges. It will
-/// update \c AliasAnalysis and \c ScalarEvolution analyses if they're non-null.
-bool simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, ScalarEvolution *SE,
-                  AssumptionCache *AC, bool PreserveLCSSA);
-
 /// \brief Put loop into LCSSA form.
 ///
 /// Looks at all instructions in the loop which have uses outside of the
diff --git a/llvm/lib/Passes/PassBuilder.cpp b/llvm/lib/Passes/PassBuilder.cpp
index d7b8eca407d..26f344c8cfe 100644
--- a/llvm/lib/Passes/PassBuilder.cpp
+++ b/llvm/lib/Passes/PassBuilder.cpp
@@ -102,6 +102,7 @@
 #include "llvm/Transforms/Scalar/TailRecursionElimination.h"
 #include "llvm/Transforms/Utils/AddDiscriminators.h"
 #include "llvm/Transforms/Utils/LCSSA.h"
+#include "llvm/Transforms/Utils/LoopSimplify.h"
 #include "llvm/Transforms/Utils/Mem2Reg.h"
 #include "llvm/Transforms/Utils/MemorySSA.h"
 #include "llvm/Transforms/Utils/SimplifyInstructions.h"
diff --git a/llvm/lib/Passes/PassRegistry.def b/llvm/lib/Passes/PassRegistry.def
index 9acb0dfed0e..18cf4841844 100644
--- a/llvm/lib/Passes/PassRegistry.def
+++ b/llvm/lib/Passes/PassRegistry.def
@@ -140,6 +140,7 @@ FUNCTION_PASS("loweratomic", LowerAtomicPass())
 FUNCTION_PASS("lower-expect", LowerExpectIntrinsicPass())
 FUNCTION_PASS("guard-widening", GuardWideningPass())
 FUNCTION_PASS("gvn", GVN())
+FUNCTION_PASS("loop-simplify", LoopSimplifyPass())
 FUNCTION_PASS("mem2reg", PromotePass())
 FUNCTION_PASS("memcpyopt", MemCpyOptPass())
 FUNCTION_PASS("mldst-motion", MergedLoadStoreMotionPass())
diff --git a/llvm/lib/Transforms/Utils/LoopSimplify.cpp b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
index 66aef29ea24..a364cab5062 100644
--- a/llvm/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
@@ -37,6 +37,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/Transforms/Utils/LoopSimplify.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/ADT/DepthFirstIterator.h"
 #include "llvm/ADT/SetOperations.h"
@@ -802,6 +803,36 @@ bool LoopSimplify::runOnFunction(Function &F) {
   return Changed;
 }
 
+PreservedAnalyses LoopSimplifyPass::run(Function &F,
+                                        AnalysisManager<Function> &AM) {
+  bool Changed = false;
+  LoopInfo *LI = &AM.getResult<LoopAnalysis>(F);
+  DominatorTree *DT = &AM.getResult<DominatorTreeAnalysis>(F);
+  ScalarEvolution *SE = AM.getCachedResult<ScalarEvolutionAnalysis>(F);
+  AssumptionCache *AC = &AM.getResult<AssumptionAnalysis>(F);
+
+  // FIXME: This pass should verify that the loops on which it's operating
+  // are in canonical SSA form, and that the pass itself preserves this form.
+  for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
+    Changed |= simplifyLoop(*I, DT, LI, SE, AC, true /* PreserveLCSSA */);
+
+  if (!Changed)
+    return PreservedAnalyses::all();
+  PreservedAnalyses PA;
+
+  // The old PM also preserved LCSSAID and BreakCriticalEdgesID.
+  // This makes no sense in the new PM so we omit those from the set
+  // of preserved passes.
+  PA.preserve<DominatorTreeAnalysis>();
+  PA.preserve<LoopAnalysis>();
+  PA.preserve<BasicAA>();
+  PA.preserve<GlobalsAA>();
+  PA.preserve<SCEVAA>();
+  PA.preserve<ScalarEvolutionAnalysis>();
+  PA.preserve<DependenceAnalysis>();
+  return PA;
+}
+
 // FIXME: Restore this code when we re-enable verification in verifyAnalysis
 // below.
 #if 0
diff --git a/llvm/lib/Transforms/Utils/LoopUnroll.cpp b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index 9e53b1c2647..7f1f78fa8b4 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -34,6 +34,7 @@
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Cloning.h"
 #include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/LoopSimplify.h"
 #include "llvm/Transforms/Utils/LoopUtils.h"
 #include "llvm/Transforms/Utils/SimplifyIndVar.h"
 using namespace llvm;
diff --git a/llvm/test/Transforms/LoopSimplify/basictest.ll b/llvm/test/Transforms/LoopSimplify/basictest.ll
index 6b31848a94b..81b2c80fae0 100644
--- a/llvm/test/Transforms/LoopSimplify/basictest.ll
+++ b/llvm/test/Transforms/LoopSimplify/basictest.ll
@@ -1,4 +1,5 @@
 ; RUN: opt < %s -loop-simplify
+; RUN: opt < %s -passes=loop-simplify
 
 ; This function should get a preheader inserted before BB3, that is jumped
 ; to by BB1 & BB2