Add a new loop-instsimplify pass, with the intention of replacing the instance

of instcombine that is currently in the middle of the loop pass pipeline. This
commit only checks in the pass; it will hopefully be enabled by default later.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122719 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 114 insertions, 0 deletions

diff --git a/lib/Transforms/Scalar/CMakeLists.txt b/lib/Transforms/Scalar/CMakeLists.txt
index 8173a31a86..68c017b9be 100644
--- a/lib/Transforms/Scalar/CMakeLists.txt
+++ b/lib/Transforms/Scalar/CMakeLists.txt
@@ -13,6 +13,7 @@ add_llvm_library(LLVMScalarOpts
   LICM.cpp
   LoopDeletion.cpp
   LoopIdiomRecognize.cpp
+  LoopInstSimplify.cpp
   LoopRotation.cpp
   LoopStrengthReduce.cpp
   LoopUnrollPass.cpp
diff --git a/lib/Transforms/Scalar/LoopInstSimplify.cpp b/lib/Transforms/Scalar/LoopInstSimplify.cpp
new file mode 100644
index 0000000000..0400288031
--- /dev/null
+++ b/lib/Transforms/Scalar/LoopInstSimplify.cpp
@@ -0,0 +1,112 @@
+//===- 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.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "loop-instsimplify"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/ADT/Statistic.h"
+using namespace llvm;
+
+STATISTIC(NumSimplified, "Number of redundant instructions simplified");
+
+namespace {
+  class LoopInstSimplify : public LoopPass {
+  public:
+    static char ID; // Pass ID, replacement for typeid
+    LoopInstSimplify() : LoopPass(ID) {
+      initializeLoopInstSimplifyPass(*PassRegistry::getPassRegistry());
+    }
+
+    bool runOnLoop(Loop*, LPPassManager&);
+
+    virtual void getAnalysisUsage(AnalysisUsage& AU) const {
+      AU.setPreservesCFG();
+      AU.addRequired<DominatorTree>();
+      AU.addPreserved<DominatorTree>();
+      AU.addRequired<LoopInfo>();
+      AU.addPreserved<LoopInfo>();
+      AU.addPreservedID(LCSSAID);
+    }
+  };
+}
+  
+char LoopInstSimplify::ID = 0;
+INITIALIZE_PASS_BEGIN(LoopInstSimplify, "loop-instsimplify",
+                "Simplify instructions in loops", false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTree)
+INITIALIZE_PASS_DEPENDENCY(LoopInfo)
+INITIALIZE_PASS_DEPENDENCY(LCSSA)
+INITIALIZE_PASS_END(LoopInstSimplify, "loop-instsimplify",
+                "Simplify instructions in loops", false, false)
+
+Pass* llvm::createLoopInstSimplifyPass() {
+  return new LoopInstSimplify();
+}
+
+bool LoopInstSimplify::runOnLoop(Loop* L, LPPassManager& LPM) {
+  DominatorTree* DT = &getAnalysis<DominatorTree>();
+  const LoopInfo* LI = &getAnalysis<LoopInfo>();
+  const TargetData* TD = getAnalysisIfAvailable<TargetData>();
+
+  bool Changed = false;
+  bool LocalChanged;
+  do {
+    LocalChanged = false;
+
+    SmallPtrSet<BasicBlock*, 32> Visited;
+    SmallVector<BasicBlock*, 32> VisitStack;
+
+    VisitStack.push_back(L->getHeader());
+
+    while (!VisitStack.empty()) {
+      BasicBlock* BB = VisitStack.back();
+      VisitStack.pop_back();
+
+      if (Visited.count(BB))
+        continue;
+      Visited.insert(BB);
+
+      for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
+        Instruction* I = BI++;
+        // Don't bother simplifying unused instructions.
+        if (!I->use_empty()) {
+          if (Value* V = SimplifyInstruction(I, TD, DT)) {
+            I->replaceAllUsesWith(V);
+            LocalChanged = true;
+            ++NumSimplified;
+          }
+        }
+        LocalChanged |= RecursivelyDeleteTriviallyDeadInstructions(I);
+      }
+      Changed |= LocalChanged;
+
+      DomTreeNode* Node = DT->getNode(BB);
+      const std::vector<DomTreeNode*>& Children = Node->getChildren();
+      for (unsigned i = 0; i < Children.size(); ++i) {
+        // Only visit children that are in the same loop.
+        BasicBlock* ChildBB = Children[i]->getBlock();
+        if (!Visited.count(ChildBB) && LI->getLoopFor(ChildBB) == L)
+          VisitStack.push_back(ChildBB);
+      }
+    }
+  } while (LocalChanged);
+
+  // Nothing that SimplifyInstruction() does should invalidate LCSSA form.
+  assert(L->isLCSSAForm(*DT));
+
+  return Changed;
+}
diff --git a/lib/Transforms/Scalar/Scalar.cpp b/lib/Transforms/Scalar/Scalar.cpp
index 27c11186d6..2b13bcacc1 100644
--- a/lib/Transforms/Scalar/Scalar.cpp
+++ b/lib/Transforms/Scalar/Scalar.cpp
@@ -41,6 +41,7 @@ void llvm::initializeScalarOpts(PassRegistry &Registry) {
   initializeJumpThreadingPass(Registry);
   initializeLICMPass(Registry);
   initializeLoopDeletionPass(Registry);
+  initializeLoopInstSimplifyPass(Registry);
   initializeLoopRotatePass(Registry);
   initializeLoopStrengthReducePass(Registry);
   initializeLoopUnrollPass(Registry);