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
diff --git a/lib/Analysis/ScalarEvolutionNormalization.cpp b/lib/Analysis/ScalarEvolutionNormalization.cpp
new file mode 100644
index 0000000..75c381d
--- /dev/null
+++ b/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;
+}