Restore the LoopInstSimplify pass, reverting r327329 that removed it.

The plan had always been to move towards using this rather than so much
in-pass simplification within the loop pipeline, but we never got around
to it.... until only a couple months after it was removed due to disuse.
=/

This commit is just a pure revert of the removal. I will add tests and
do some basic cleanup in follow-up commits. Then I'll wire it into the
loop pass pipeline.

Differential Revision: https://reviews.llvm.org/D47353

llvm-svn: 333250

llvm/include/llvm/InitializePasses.h

@@ -215,6 +215,7 @@ void initializeLoopDistributeLegacyPass(PassRegistry&);
 void initializeLoopExtractorPass(PassRegistry&);
 void initializeLoopIdiomRecognizeLegacyPassPass(PassRegistry&);
 void initializeLoopInfoWrapperPassPass(PassRegistry&);
+void initializeLoopInstSimplifyLegacyPassPass(PassRegistry&);
 void initializeLoopInterchangePass(PassRegistry&);
 void initializeLoopLoadEliminationPass(PassRegistry&);
 void initializeLoopPassPass(PassRegistry&);

llvm/include/llvm/Transforms/Scalar.h

@@ -174,6 +174,12 @@ Pass *createLoopStrengthReducePass();
 Pass *createLoopUnswitchPass(bool OptimizeForSize = false,
                              bool hasBranchDivergence = false);
 
+//===----------------------------------------------------------------------===//
+//
+// LoopInstSimplify - This pass simplifies instructions in a loop's body.
+//
+Pass *createLoopInstSimplifyPass();
+
 //===----------------------------------------------------------------------===//
 //
 // LoopUnroll - This pass is a simple loop unrolling pass.

llvm/include/llvm/Transforms/Scalar/LoopInstSimplify.h

@@ -0,0 +1,34 @@
+//===- LoopInstSimplify.h - Loop Inst Simplify 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 lightweight instruction simplification on loop bodies.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_SCALAR_LOOPINSTSIMPLIFY_H
+#define LLVM_TRANSFORMS_SCALAR_LOOPINSTSIMPLIFY_H
+
+#include "llvm/Analysis/LoopAnalysisManager.h"
+#include "llvm/IR/PassManager.h"
+
+namespace llvm {
+
+class Loop;
+class LPMUpdater;
+
+/// Performs Loop Inst Simplify Pass.
+class LoopInstSimplifyPass : public PassInfoMixin<LoopInstSimplifyPass> {
+public:
+  PreservedAnalyses run(Loop &L, LoopAnalysisManager &AM,
+                        LoopStandardAnalysisResults &AR, LPMUpdater &U);
+};
+
+} // end namespace llvm
+
+#endif // LLVM_TRANSFORMS_SCALAR_LOOPINSTSIMPLIFY_H

llvm/lib/Passes/PassBuilder.cpp

@@ -111,6 +111,7 @@
 #include "llvm/Transforms/Scalar/LoopDeletion.h"
 #include "llvm/Transforms/Scalar/LoopDistribute.h"
 #include "llvm/Transforms/Scalar/LoopIdiomRecognize.h"
+#include "llvm/Transforms/Scalar/LoopInstSimplify.h"
 #include "llvm/Transforms/Scalar/LoopLoadElimination.h"
 #include "llvm/Transforms/Scalar/LoopPassManager.h"
 #include "llvm/Transforms/Scalar/LoopPredication.h"
@@ -391,8 +392,9 @@ PassBuilder::buildFunctionSimplificationPipeline(OptimizationLevel Level,
   // FIXME: Currently this is split into two loop pass pipelines because we run
   // some function passes in between them. These can and should be replaced by
   // loop pass equivalenst but those aren't ready yet. Specifically,
-  // `SimplifyCFGPass` and `InstCombinePass` are used. We just have
-  // `LoopSimplifyCFGPass` which isn't yet powerful enough.
+  // `SimplifyCFGPass` and `InstCombinePass` are used. We have
+  // `LoopSimplifyCFGPass` which isn't yet powerful enough, and the closest to
+  // the other we have is `LoopInstSimplify`.
   LoopPassManager LPM1(DebugLogging), LPM2(DebugLogging);
 
   // Rotate Loop - disable header duplication at -Oz

llvm/lib/Passes/PassRegistry.def

@@ -230,6 +230,7 @@ LOOP_ANALYSIS("ivusers", IVUsersAnalysis())
 LOOP_PASS("invalidate<all>", InvalidateAllAnalysesPass())
 LOOP_PASS("licm", LICMPass())
 LOOP_PASS("loop-idiom", LoopIdiomRecognizePass())
+LOOP_PASS("loop-instsimplify", LoopInstSimplifyPass())
 LOOP_PASS("rotate", LoopRotatePass())
 LOOP_PASS("no-op-loop", NoOpLoopPass())
 LOOP_PASS("print", PrintLoopPass(dbgs()))

llvm/lib/Transforms/Scalar/CMakeLists.txt

@@ -28,6 +28,7 @@ add_llvm_library(LLVMScalarOpts
   LoopDataPrefetch.cpp
   LoopDistribute.cpp
   LoopIdiomRecognize.cpp
+  LoopInstSimplify.cpp
   LoopInterchange.cpp
   LoopLoadElimination.cpp
   LoopPassManager.cpp

llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp

@@ -0,0 +1,223 @@
+//===- LoopInstSimplify.cpp - Loop Instruction Simplification Pass --------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass performs lightweight instruction simplification on loop bodies.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar/LoopInstSimplify.h"
+#include "llvm/ADT/PointerIntPair.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Analysis/Utils/Local.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/IR/User.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
+#include <algorithm>
+#include <utility>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "loop-instsimplify"
+
+STATISTIC(NumSimplified, "Number of redundant instructions simplified");
+
+static bool SimplifyLoopInst(Loop *L, DominatorTree *DT, LoopInfo *LI,
+                             AssumptionCache *AC,
+                             const TargetLibraryInfo *TLI) {
+  SmallVector<BasicBlock *, 8> ExitBlocks;
+  L->getUniqueExitBlocks(ExitBlocks);
+  array_pod_sort(ExitBlocks.begin(), ExitBlocks.end());
+
+  SmallPtrSet<const Instruction *, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
+
+  // The bit we are stealing from the pointer represents whether this basic
+  // block is the header of a subloop, in which case we only process its phis.
+  using WorklistItem = PointerIntPair<BasicBlock *, 1>;
+  SmallVector<WorklistItem, 16> VisitStack;
+  SmallPtrSet<BasicBlock *, 32> Visited;
+
+  bool Changed = false;
+  bool LocalChanged;
+  do {
+    LocalChanged = false;
+
+    VisitStack.clear();
+    Visited.clear();
+
+    VisitStack.push_back(WorklistItem(L->getHeader(), false));
+
+    while (!VisitStack.empty()) {
+      WorklistItem Item = VisitStack.pop_back_val();
+      BasicBlock *BB = Item.getPointer();
+      bool IsSubloopHeader = Item.getInt();
+      const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
+
+      // Simplify instructions in the current basic block.
+      for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
+        Instruction *I = &*BI++;
+
+        // The first time through the loop ToSimplify is empty and we try to
+        // simplify all instructions. On later iterations ToSimplify is not
+        // empty and we only bother simplifying instructions that are in it.
+        if (!ToSimplify->empty() && !ToSimplify->count(I))
+          continue;
+
+        // Don't bother simplifying unused instructions.
+        if (!I->use_empty()) {
+          Value *V = SimplifyInstruction(I, {DL, TLI, DT, AC});
+          if (V && LI->replacementPreservesLCSSAForm(I, V)) {
+            // Mark all uses for resimplification next time round the loop.
+            for (User *U : I->users())
+              Next->insert(cast<Instruction>(U));
+
+            I->replaceAllUsesWith(V);
+            LocalChanged = true;
+            ++NumSimplified;
+          }
+        }
+        if (RecursivelyDeleteTriviallyDeadInstructions(I, TLI)) {
+          // RecursivelyDeleteTriviallyDeadInstruction can remove more than one
+          // instruction, so simply incrementing the iterator does not work.
+          // When instructions get deleted re-iterate instead.
+          BI = BB->begin();
+          BE = BB->end();
+          LocalChanged = true;
+        }
+
+        if (IsSubloopHeader && !isa<PHINode>(I))
+          break;
+      }
+
+      // Add all successors to the worklist, except for loop exit blocks and the
+      // bodies of subloops. We visit the headers of loops so that we can
+      // process
+      // their phis, but we contract the rest of the subloop body and only
+      // follow
+      // edges leading back to the original loop.
+      for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE;
+           ++SI) {
+        BasicBlock *SuccBB = *SI;
+        if (!Visited.insert(SuccBB).second)
+          continue;
+
+        const Loop *SuccLoop = LI->getLoopFor(SuccBB);
+        if (SuccLoop && SuccLoop->getHeader() == SuccBB &&
+            L->contains(SuccLoop)) {
+          VisitStack.push_back(WorklistItem(SuccBB, true));
+
+          SmallVector<BasicBlock *, 8> SubLoopExitBlocks;
+          SuccLoop->getExitBlocks(SubLoopExitBlocks);
+
+          for (unsigned i = 0; i < SubLoopExitBlocks.size(); ++i) {
+            BasicBlock *ExitBB = SubLoopExitBlocks[i];
+            if (LI->getLoopFor(ExitBB) == L && Visited.insert(ExitBB).second)
+              VisitStack.push_back(WorklistItem(ExitBB, false));
+          }
+
+          continue;
+        }
+
+        bool IsExitBlock =
+            std::binary_search(ExitBlocks.begin(), ExitBlocks.end(), SuccBB);
+        if (IsExitBlock)
+          continue;
+
+        VisitStack.push_back(WorklistItem(SuccBB, false));
+      }
+    }
+
+    // Place the list of instructions to simplify on the next loop iteration
+    // into ToSimplify.
+    std::swap(ToSimplify, Next);
+    Next->clear();
+
+    Changed |= LocalChanged;
+  } while (LocalChanged);
+
+  return Changed;
+}
+
+namespace {
+
+class LoopInstSimplifyLegacyPass : public LoopPass {
+public:
+  static char ID; // Pass ID, replacement for typeid
+
+  LoopInstSimplifyLegacyPass() : LoopPass(ID) {
+    initializeLoopInstSimplifyLegacyPassPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnLoop(Loop *L, LPPassManager &LPM) override {
+    if (skipLoop(L))
+      return false;
+    DominatorTreeWrapperPass *DTWP =
+        getAnalysisIfAvailable<DominatorTreeWrapperPass>();
+    DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
+    LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+    AssumptionCache *AC =
+        &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(
+            *L->getHeader()->getParent());
+    const TargetLibraryInfo *TLI =
+        &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
+
+    return SimplifyLoopInst(L, DT, LI, AC, TLI);
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.addRequired<AssumptionCacheTracker>();
+    AU.addRequired<TargetLibraryInfoWrapperPass>();
+    AU.setPreservesCFG();
+    getLoopAnalysisUsage(AU);
+  }
+};
+
+} // end anonymous namespace
+
+PreservedAnalyses LoopInstSimplifyPass::run(Loop &L, LoopAnalysisManager &AM,
+                                            LoopStandardAnalysisResults &AR,
+                                            LPMUpdater &) {
+  if (!SimplifyLoopInst(&L, &AR.DT, &AR.LI, &AR.AC, &AR.TLI))
+    return PreservedAnalyses::all();
+
+  auto PA = getLoopPassPreservedAnalyses();
+  PA.preserveSet<CFGAnalyses>();
+  return PA;
+}
+
+char LoopInstSimplifyLegacyPass::ID = 0;
+
+INITIALIZE_PASS_BEGIN(LoopInstSimplifyLegacyPass, "loop-instsimplify",
+                      "Simplify instructions in loops", false, false)
+INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_END(LoopInstSimplifyLegacyPass, "loop-instsimplify",
+                    "Simplify instructions in loops", false, false)
+
+Pass *llvm::createLoopInstSimplifyPass() {
+  return new LoopInstSimplifyLegacyPass();
+}

llvm/lib/Transforms/Scalar/Scalar.cpp

@@ -62,6 +62,7 @@ void llvm::initializeScalarOpts(PassRegistry &Registry) {
   initializeLoopDataPrefetchLegacyPassPass(Registry);
   initializeLoopDeletionLegacyPassPass(Registry);
   initializeLoopAccessLegacyAnalysisPass(Registry);
+  initializeLoopInstSimplifyLegacyPassPass(Registry);
   initializeLoopInterchangePass(Registry);
   initializeLoopPredicationLegacyPassPass(Registry);
   initializeLoopRotateLegacyPassPass(Registry);

llvm/test/Feature/optnone-opt.ll

@@ -3,7 +3,7 @@
 ; RUN: opt -O2 -S -debug %s 2>&1 | FileCheck %s --check-prefix=OPT-O1 --check-prefix=OPT-O2O3
 ; RUN: opt -O3 -S -debug %s 2>&1 | FileCheck %s --check-prefix=OPT-O1 --check-prefix=OPT-O2O3
 ; RUN: opt -dce -die -gvn-hoist -loweratomic -S -debug %s 2>&1 | FileCheck %s --check-prefix=OPT-MORE
-; RUN: opt -indvars -licm -loop-deletion -loop-extract -loop-idiom -loop-reduce -loop-reroll -loop-rotate -loop-unroll -loop-unswitch -S -debug %s 2>&1 | FileCheck %s --check-prefix=OPT-LOOP
+; RUN: opt -indvars -licm -loop-deletion -loop-extract -loop-idiom -loop-instsimplify -loop-reduce -loop-reroll -loop-rotate -loop-unroll -loop-unswitch -S -debug %s 2>&1 | FileCheck %s --check-prefix=OPT-LOOP
 
 ; REQUIRES: asserts
 
@@ -67,5 +67,6 @@ attributes #0 = { optnone noinline }
 ; OPT-LOOP-DAG: Skipping pass 'Recognize loop idioms'
 ; OPT-LOOP-DAG: Skipping pass 'Reroll loops'
 ; OPT-LOOP-DAG: Skipping pass 'Rotate Loops'
+; OPT-LOOP-DAG: Skipping pass 'Simplify instructions in loops'
 ; OPT-LOOP-DAG: Skipping pass 'Unroll loops'
 ; OPT-LOOP-DAG: Skipping pass 'Unswitch loops'