Break SCEVExpander out of IndVarSimplify into its own .h/.cpp file so that

other passes may use it.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22557 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ScalarEvolutionExpander.cpp

@@ -0,0 +1,105 @@
+//===- ScalarEvolutionExpander.cpp - Scalar Evolution Analysis --*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains the implementation of the scalar evolution expander,
+// which is used to generate the code corresponding to a given scalar evolution
+// expression.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/ScalarEvolutionExpander.h"
+using namespace llvm;
+
+Value *SCEVExpander::visitMulExpr(SCEVMulExpr *S) {
+  const Type *Ty = S->getType();
+  int FirstOp = 0;  // Set if we should emit a subtract.
+  if (SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getOperand(0)))
+    if (SC->getValue()->isAllOnesValue())
+      FirstOp = 1;
+
+  int i = S->getNumOperands()-2;
+  Value *V = expandInTy(S->getOperand(i+1), Ty);
+
+  // Emit a bunch of multiply instructions
+  for (; i >= FirstOp; --i)
+    V = BinaryOperator::createMul(V, expandInTy(S->getOperand(i), Ty),
+                                  "tmp.", InsertPt);
+  // -1 * ...  --->  0 - ...
+  if (FirstOp == 1)
+    V = BinaryOperator::createNeg(V, "tmp.", InsertPt);
+  return V;
+}
+
+Value *SCEVExpander::visitAddRecExpr(SCEVAddRecExpr *S) {
+  const Type *Ty = S->getType();
+  const Loop *L = S->getLoop();
+  // We cannot yet do fp recurrences, e.g. the xform of {X,+,F} --> X+{0,+,F}
+  assert(Ty->isIntegral() && "Cannot expand fp recurrences yet!");
+
+  // {X,+,F} --> X + {0,+,F}
+  if (!isa<SCEVConstant>(S->getStart()) ||
+      !cast<SCEVConstant>(S->getStart())->getValue()->isNullValue()) {
+    Value *Start = expandInTy(S->getStart(), Ty);
+    std::vector<SCEVHandle> NewOps(S->op_begin(), S->op_end());
+    NewOps[0] = SCEVUnknown::getIntegerSCEV(0, Ty);
+    Value *Rest = expandInTy(SCEVAddRecExpr::get(NewOps, L), Ty);
+
+    // FIXME: look for an existing add to use.
+    return BinaryOperator::createAdd(Rest, Start, "tmp.", InsertPt);
+  }
+
+  // {0,+,1} --> Insert a canonical induction variable into the loop!
+  if (S->getNumOperands() == 2 &&
+      S->getOperand(1) == SCEVUnknown::getIntegerSCEV(1, Ty)) {
+    // Create and insert the PHI node for the induction variable in the
+    // specified loop.
+    BasicBlock *Header = L->getHeader();
+    PHINode *PN = new PHINode(Ty, "indvar", Header->begin());
+    PN->addIncoming(Constant::getNullValue(Ty), L->getLoopPreheader());
+
+    pred_iterator HPI = pred_begin(Header);
+    assert(HPI != pred_end(Header) && "Loop with zero preds???");
+    if (!L->contains(*HPI)) ++HPI;
+    assert(HPI != pred_end(Header) && L->contains(*HPI) &&
+           "No backedge in loop?");
+
+    // Insert a unit add instruction right before the terminator corresponding
+    // to the back-edge.
+    Constant *One = Ty->isFloatingPoint() ? (Constant*)ConstantFP::get(Ty, 1.0)
+                                          : ConstantInt::get(Ty, 1);
+    Instruction *Add = BinaryOperator::createAdd(PN, One, "indvar.next",
+                                                 (*HPI)->getTerminator());
+
+    pred_iterator PI = pred_begin(Header);
+    if (*PI == L->getLoopPreheader())
+      ++PI;
+    PN->addIncoming(Add, *PI);
+    return PN;
+  }
+
+  // Get the canonical induction variable I for this loop.
+  Value *I = getOrInsertCanonicalInductionVariable(L, Ty);
+
+  if (S->getNumOperands() == 2) {   // {0,+,F} --> i*F
+    Value *F = expandInTy(S->getOperand(1), Ty);
+    return BinaryOperator::createMul(I, F, "tmp.", InsertPt);
+  }
+
+  // If this is a chain of recurrences, turn it into a closed form, using the
+  // folders, then expandCodeFor the closed form.  This allows the folders to
+  // simplify the expression without having to build a bunch of special code
+  // into this folder.
+  SCEVHandle IH = SCEVUnknown::get(I);   // Get I as a "symbolic" SCEV.
+
+  SCEVHandle V = S->evaluateAtIteration(IH);
+  //std::cerr << "Evaluated: " << *this << "\n     to: " << *V << "\n";
+
+  return expandInTy(V, Ty);
+}