Import LLVM, at r72732.

1 files changed, 183 insertions, 0 deletions

diff --git a/lib/Transforms/Scalar/LoopUnroll.cpp b/lib/Transforms/Scalar/LoopUnroll.cpp
new file mode 100644
index 0000000..23757cd
--- /dev/null
+++ b/lib/Transforms/Scalar/LoopUnroll.cpp
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+//===-- LoopUnroll.cpp - Loop unroller pass -------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass implements a simple loop unroller.  It works best when loops have
+// been canonicalized by the -indvars pass, allowing it to determine the trip
+// counts of loops easily.
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "loop-unroll"
+#include "llvm/IntrinsicInst.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Transforms/Utils/UnrollLoop.h"
+#include <climits>
+
+using namespace llvm;
+
+static cl::opt<unsigned>
+UnrollThreshold("unroll-threshold", cl::init(100), cl::Hidden,
+  cl::desc("The cut-off point for automatic loop unrolling"));
+
+static cl::opt<unsigned>
+UnrollCount("unroll-count", cl::init(0), cl::Hidden,
+  cl::desc("Use this unroll count for all loops, for testing purposes"));
+
+static cl::opt<bool>
+UnrollAllowPartial("unroll-allow-partial", cl::init(false), cl::Hidden,
+  cl::desc("Allows loops to be partially unrolled until "
+           "-unroll-threshold loop size is reached."));
+
+namespace {
+  class VISIBILITY_HIDDEN LoopUnroll : public LoopPass {
+  public:
+    static char ID; // Pass ID, replacement for typeid
+    LoopUnroll() : LoopPass(&ID) {}
+
+    /// A magic value for use with the Threshold parameter to indicate
+    /// that the loop unroll should be performed regardless of how much
+    /// code expansion would result.
+    static const unsigned NoThreshold = UINT_MAX;
+
+    bool runOnLoop(Loop *L, LPPassManager &LPM);
+
+    /// This transformation requires natural loop information & requires that
+    /// loop preheaders be inserted into the CFG...
+    ///
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.addRequiredID(LoopSimplifyID);
+      AU.addRequiredID(LCSSAID);
+      AU.addRequired<LoopInfo>();
+      AU.addPreservedID(LCSSAID);
+      AU.addPreserved<LoopInfo>();
+      // FIXME: Loop unroll requires LCSSA. And LCSSA requires dom info.
+      // If loop unroll does not preserve dom info then LCSSA pass on next
+      // loop will receive invalid dom info.
+      // For now, recreate dom info, if loop is unrolled.
+      AU.addPreserved<DominatorTree>();
+      AU.addPreserved<DominanceFrontier>();
+    }
+  };
+}
+
+char LoopUnroll::ID = 0;
+static RegisterPass<LoopUnroll> X("loop-unroll", "Unroll loops");
+
+Pass *llvm::createLoopUnrollPass() { return new LoopUnroll(); }
+
+/// ApproximateLoopSize - Approximate the size of the loop.
+static unsigned ApproximateLoopSize(const Loop *L) {
+  unsigned Size = 0;
+  for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
+       I != E; ++I) {
+    BasicBlock *BB = *I;
+    Instruction *Term = BB->getTerminator();
+    for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
+      if (isa<PHINode>(I) && BB == L->getHeader()) {
+        // Ignore PHI nodes in the header.
+      } else if (I->hasOneUse() && I->use_back() == Term) {
+        // Ignore instructions only used by the loop terminator.
+      } else if (isa<DbgInfoIntrinsic>(I)) {
+        // Ignore debug instructions
+      } else if (isa<GetElementPtrInst>(I) && I->hasOneUse()) {
+        // Ignore GEP as they generally are subsumed into a load or store.
+      } else if (isa<CallInst>(I)) {
+        // Estimate size overhead introduced by call instructions which
+        // is higher than other instructions. Here 3 and 10 are magic
+        // numbers that help one isolated test case from PR2067 without
+        // negatively impacting measured benchmarks.
+        if (isa<IntrinsicInst>(I))
+          Size = Size + 3;
+        else
+          Size = Size + 10;
+      } else {
+        ++Size;
+      }
+
+      // TODO: Ignore expressions derived from PHI and constants if inval of phi
+      // is a constant, or if operation is associative.  This will get induction
+      // variables.
+    }
+  }
+
+  return Size;
+}
+
+bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
+  assert(L->isLCSSAForm());
+  LoopInfo *LI = &getAnalysis<LoopInfo>();
+
+  BasicBlock *Header = L->getHeader();
+  DOUT << "Loop Unroll: F[" << Header->getParent()->getName()
+       << "] Loop %" << Header->getName() << "\n";
+
+  // Find trip count
+  unsigned TripCount = L->getSmallConstantTripCount();
+  unsigned Count = UnrollCount;
+ 
+  // Automatically select an unroll count.
+  if (Count == 0) {
+    // Conservative heuristic: if we know the trip count, see if we can
+    // completely unroll (subject to the threshold, checked below); otherwise
+    // try to find greatest modulo of the trip count which is still under 
+    // threshold value.
+    if (TripCount != 0) {
+      Count = TripCount;
+    } else {
+      return false;
+    }
+  }
+
+  // Enforce the threshold.
+  if (UnrollThreshold != NoThreshold) {
+    unsigned LoopSize = ApproximateLoopSize(L);
+    DOUT << "  Loop Size = " << LoopSize << "\n";
+    uint64_t Size = (uint64_t)LoopSize*Count;
+    if (TripCount != 1 && Size > UnrollThreshold) {
+      DOUT << "  Too large to fully unroll with count: " << Count
+           << " because size: " << Size << ">" << UnrollThreshold << "\n";
+      if (UnrollAllowPartial) {
+        // Reduce unroll count to be modulo of TripCount for partial unrolling
+        Count = UnrollThreshold / LoopSize;        
+        while (Count != 0 && TripCount%Count != 0) {
+          Count--;
+        }        
+        if (Count < 2) {
+          DOUT << "  could not unroll partially\n";
+          return false;
+        } else {
+          DOUT << "  partially unrolling with count: " << Count << "\n";
+        }
+      } else {
+        DOUT << "  will not try to unroll partially because "
+             << "-unroll-allow-partial not given\n";
+        return false;
+      }
+    }
+  }
+
+  // Unroll the loop.
+  Function *F = L->getHeader()->getParent();
+  if (!UnrollLoop(L, Count, LI, &LPM))
+    return false;
+
+  // FIXME: Reconstruct dom info, because it is not preserved properly.
+  DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>();
+  if (DT) {
+    DT->runOnFunction(*F);
+    DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>();
+    if (DF)
+      DF->runOnFunction(*F);
+  }
+  return true;
+}