Generalize IVUsers to track arbitrary expressions rather than expressions

explicitly split into stride-and-offset pairs. Also, add the
ability to track multiple post-increment loops on the same expression.

This refines the concept of "normalizing" SCEV expressions used for
to post-increment uses, and introduces a dedicated utility routine for
normalizing and denormalizing expressions.

This fixes the expansion of expressions which are post-increment users
of more than one loop at a time. More broadly, this takes LSR another
step closer to being able to reason about more than one loop at a time.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@100699 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ScalarEvolutionNormalization.cpp

@@ -0,0 +1,150 @@
+//===- ScalarEvolutionNormalization.cpp - See below -------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements utilities for working with "normalized" expressions.
+// See the comments at the top of ScalarEvolutionNormalization.h for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Analysis/ScalarEvolutionNormalization.h"
+using namespace llvm;
+
+/// IVUseShouldUsePostIncValue - We have discovered a "User" of an IV expression
+/// and now we need to decide whether the user should use the preinc or post-inc
+/// value.  If this user should use the post-inc version of the IV, return true.
+///
+/// Choosing wrong here can break dominance properties (if we choose to use the
+/// post-inc value when we cannot) or it can end up adding extra live-ranges to
+/// the loop, resulting in reg-reg copies (if we use the pre-inc value when we
+/// should use the post-inc value).
+static bool IVUseShouldUsePostIncValue(Instruction *User, Instruction *IV,
+                                       const Loop *L, DominatorTree *DT) {
+  // If the user is in the loop, use the preinc value.
+  if (L->contains(User)) return false;
+
+  BasicBlock *LatchBlock = L->getLoopLatch();
+  if (!LatchBlock)
+    return false;
+
+  // Ok, the user is outside of the loop.  If it is dominated by the latch
+  // block, use the post-inc value.
+  if (DT->dominates(LatchBlock, User->getParent()))
+    return true;
+
+  // There is one case we have to be careful of: PHI nodes.  These little guys
+  // can live in blocks that are not dominated by the latch block, but (since
+  // their uses occur in the predecessor block, not the block the PHI lives in)
+  // should still use the post-inc value.  Check for this case now.
+  PHINode *PN = dyn_cast<PHINode>(User);
+  if (!PN) return false;  // not a phi, not dominated by latch block.
+
+  // Look at all of the uses of IV by the PHI node.  If any use corresponds to
+  // a block that is not dominated by the latch block, give up and use the
+  // preincremented value.
+  unsigned NumUses = 0;
+  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+    if (PN->getIncomingValue(i) == IV) {
+      ++NumUses;
+      if (!DT->dominates(LatchBlock, PN->getIncomingBlock(i)))
+        return false;
+    }
+
+  // Okay, all uses of IV by PN are in predecessor blocks that really are
+  // dominated by the latch block.  Use the post-incremented value.
+  return true;
+}
+
+const SCEV *llvm::TransformForPostIncUse(TransformKind Kind,
+                                         const SCEV *S,
+                                         Instruction *User,
+                                         Value *OperandValToReplace,
+                                         PostIncLoopSet &Loops,
+                                         ScalarEvolution &SE,
+                                         DominatorTree &DT) {
+  if (isa<SCEVConstant>(S) || isa<SCEVUnknown>(S))
+    return S;
+  if (const SCEVCastExpr *X = dyn_cast<SCEVCastExpr>(S)) {
+    const SCEV *O = X->getOperand();
+    const SCEV *N = TransformForPostIncUse(Kind, O, User, OperandValToReplace,
+                                           Loops, SE, DT);
+    if (O != N)
+      switch (S->getSCEVType()) {
+      case scZeroExtend: return SE.getZeroExtendExpr(N, S->getType());
+      case scSignExtend: return SE.getSignExtendExpr(N, S->getType());
+      case scTruncate: return SE.getTruncateExpr(N, S->getType());
+      default: llvm_unreachable("Unexpected SCEVCastExpr kind!");
+      }
+    return S;
+  }
+  if (const SCEVNAryExpr *X = dyn_cast<SCEVNAryExpr>(S)) {
+    SmallVector<const SCEV *, 8> Operands;
+    bool Changed = false;
+    for (SCEVNAryExpr::op_iterator I = X->op_begin(), E = X->op_end();
+         I != E; ++I) {
+      const SCEV *O = *I;
+      const SCEV *N = TransformForPostIncUse(Kind, O, User, OperandValToReplace,
+                                             Loops, SE, DT);
+      Changed |= N != O;
+      Operands.push_back(N);
+    }
+    if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
+      // An addrec. This is the interesting part.
+      const Loop *L = AR->getLoop();
+      const SCEV *Result = SE.getAddRecExpr(Operands, L);
+      switch (Kind) {
+      default: llvm_unreachable("Unexpected transform name!");
+      case NormalizeAutodetect:
+        if (Instruction *OI = dyn_cast<Instruction>(OperandValToReplace))
+          if (IVUseShouldUsePostIncValue(User, OI, L, &DT)) {
+            Result = SE.getMinusSCEV(Result, AR->getStepRecurrence(SE));
+            Loops.insert(L);
+          }
+        break;
+      case Normalize:
+        if (Loops.count(L))
+          Result = SE.getMinusSCEV(Result, AR->getStepRecurrence(SE));
+        break;
+      case Denormalize:
+        if (Loops.count(L)) {
+          const SCEV *TransformedStep =
+            TransformForPostIncUse(Kind, AR->getStepRecurrence(SE),
+                                   User, OperandValToReplace, Loops, SE, DT);
+          Result = SE.getAddExpr(Result, TransformedStep);
+        }
+        break;
+      }
+      return Result;
+    }
+    if (Changed)
+      switch (S->getSCEVType()) {
+      case scAddExpr: return SE.getAddExpr(Operands);
+      case scMulExpr: return SE.getMulExpr(Operands);
+      case scSMaxExpr: return SE.getSMaxExpr(Operands);
+      case scUMaxExpr: return SE.getUMaxExpr(Operands);
+      default: llvm_unreachable("Unexpected SCEVNAryExpr kind!");
+      }
+    return S;
+  }
+  if (const SCEVUDivExpr *X = dyn_cast<SCEVUDivExpr>(S)) {
+    const SCEV *LO = X->getLHS();
+    const SCEV *RO = X->getRHS();
+    const SCEV *LN = TransformForPostIncUse(Kind, LO, User, OperandValToReplace,
+                                            Loops, SE, DT);
+    const SCEV *RN = TransformForPostIncUse(Kind, RO, User, OperandValToReplace,
+                                            Loops, SE, DT);
+    if (LO != LN || RO != RN)
+      return SE.getUDivExpr(LN, RN);
+    return S;
+  }
+  llvm_unreachable("Unexpected SCEV kind!");
+  return 0;
+}