llvm-mirror/include/llvm/Transforms/Utils/Local.h

//===-- Local.h - Functions to perform local transformations ----*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This family of functions perform various local transformations to the
// program.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_TRANSFORMS_UTILS_LOCAL_H
#define LLVM_TRANSFORMS_UTILS_LOCAL_H

#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Operator.h"

namespace llvm {

class User;
class BasicBlock;
class Function;
class BranchInst;
class Instruction;
class DbgDeclareInst;
class StoreInst;
class LoadInst;
class Value;
class PHINode;
class AllocaInst;
class AssumptionCache;
class ConstantExpr;
class DataLayout;
class TargetLibraryInfo;
class TargetTransformInfo;
class DIBuilder;
class DominatorTree;

template<typename T> class SmallVectorImpl;

//===----------------------------------------------------------------------===//
//  Local constant propagation.
//

/// ConstantFoldTerminator - If a terminator instruction is predicated on a
/// constant value, convert it into an unconditional branch to the constant
/// destination.  This is a nontrivial operation because the successors of this
/// basic block must have their PHI nodes updated.
/// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
/// conditions and indirectbr addresses this might make dead if
/// DeleteDeadConditions is true.
bool ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions = false,
                            const TargetLibraryInfo *TLI = nullptr);

//===----------------------------------------------------------------------===//
//  Local dead code elimination.
//

/// isInstructionTriviallyDead - Return true if the result produced by the
/// instruction is not used, and the instruction has no side effects.
///
bool isInstructionTriviallyDead(Instruction *I,
                                const TargetLibraryInfo *TLI = nullptr);

/// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
/// trivially dead instruction, delete it.  If that makes any of its operands
/// trivially dead, delete them too, recursively.  Return true if any
/// instructions were deleted.
bool RecursivelyDeleteTriviallyDeadInstructions(Value *V,
                                        const TargetLibraryInfo *TLI = nullptr);

/// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
/// dead PHI node, due to being a def-use chain of single-use nodes that
/// either forms a cycle or is terminated by a trivially dead instruction,
/// delete it.  If that makes any of its operands trivially dead, delete them
/// too, recursively.  Return true if a change was made.
bool RecursivelyDeleteDeadPHINode(PHINode *PN,
                                  const TargetLibraryInfo *TLI = nullptr);

/// SimplifyInstructionsInBlock - Scan the specified basic block and try to
/// simplify any instructions in it and recursively delete dead instructions.
///
/// This returns true if it changed the code, note that it can delete
/// instructions in other blocks as well in this block.
bool SimplifyInstructionsInBlock(BasicBlock *BB,
                                 const TargetLibraryInfo *TLI = nullptr);

//===----------------------------------------------------------------------===//
//  Control Flow Graph Restructuring.
//

/// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
/// method is called when we're about to delete Pred as a predecessor of BB.  If
/// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
///
/// Unlike the removePredecessor method, this attempts to simplify uses of PHI
/// nodes that collapse into identity values.  For example, if we have:
///   x = phi(1, 0, 0, 0)
///   y = and x, z
///
/// .. and delete the predecessor corresponding to the '1', this will attempt to
/// recursively fold the 'and' to 0.
void RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred);

/// MergeBasicBlockIntoOnlyPred - BB is a block with one predecessor and its
/// predecessor is known to have one successor (BB!).  Eliminate the edge
/// between them, moving the instructions in the predecessor into BB.  This
/// deletes the predecessor block.
///
void MergeBasicBlockIntoOnlyPred(BasicBlock *BB, DominatorTree *DT = nullptr);

/// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
/// unconditional branch, and contains no instructions other than PHI nodes,
/// potential debug intrinsics and the branch.  If possible, eliminate BB by
/// rewriting all the predecessors to branch to the successor block and return
/// true.  If we can't transform, return false.
bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB);

/// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
/// nodes in this block. This doesn't try to be clever about PHI nodes
/// which differ only in the order of the incoming values, but instcombine
/// orders them so it usually won't matter.
///
bool EliminateDuplicatePHINodes(BasicBlock *BB);

/// SimplifyCFG - This function is used to do simplification of a CFG.  For
/// example, it adjusts branches to branches to eliminate the extra hop, it
/// eliminates unreachable basic blocks, and does other "peephole" optimization
/// of the CFG.  It returns true if a modification was made, possibly deleting
/// the basic block that was pointed to.
///
bool SimplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI,
                 unsigned BonusInstThreshold, AssumptionCache *AC = nullptr);

/// FlatternCFG - This function is used to flatten a CFG.  For
/// example, it uses parallel-and and parallel-or mode to collapse
//  if-conditions and merge if-regions with identical statements.
///
bool FlattenCFG(BasicBlock *BB, AliasAnalysis *AA = nullptr);

/// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
/// and if a predecessor branches to us and one of our successors, fold the
/// setcc into the predecessor and use logical operations to pick the right
/// destination.
bool FoldBranchToCommonDest(BranchInst *BI, unsigned BonusInstThreshold = 1);

/// DemoteRegToStack - This function takes a virtual register computed by an
/// Instruction and replaces it with a slot in the stack frame, allocated via
/// alloca.  This allows the CFG to be changed around without fear of
/// invalidating the SSA information for the value.  It returns the pointer to
/// the alloca inserted to create a stack slot for X.
///
AllocaInst *DemoteRegToStack(Instruction &X,
                             bool VolatileLoads = false,
                             Instruction *AllocaPoint = nullptr);

/// DemotePHIToStack - This function takes a virtual register computed by a phi
/// node and replaces it with a slot in the stack frame, allocated via alloca.
/// The phi node is deleted and it returns the pointer to the alloca inserted.
AllocaInst *DemotePHIToStack(PHINode *P, Instruction *AllocaPoint = nullptr);

/// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
/// we can determine, return it, otherwise return 0.  If PrefAlign is specified,
/// and it is more than the alignment of the ultimate object, see if we can
/// increase the alignment of the ultimate object, making this check succeed.
unsigned getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
                                    const DataLayout &DL,
                                    const Instruction *CxtI = nullptr,
                                    AssumptionCache *AC = nullptr,
                                    const DominatorTree *DT = nullptr);

/// getKnownAlignment - Try to infer an alignment for the specified pointer.
static inline unsigned getKnownAlignment(Value *V, const DataLayout &DL,
                                         const Instruction *CxtI = nullptr,
                                         AssumptionCache *AC = nullptr,
                                         const DominatorTree *DT = nullptr) {
  return getOrEnforceKnownAlignment(V, 0, DL, CxtI, AC, DT);
}

/// EmitGEPOffset - Given a getelementptr instruction/constantexpr, emit the
/// code necessary to compute the offset from the base pointer (without adding
/// in the base pointer).  Return the result as a signed integer of intptr size.
/// When NoAssumptions is true, no assumptions about index computation not
/// overflowing is made.
template <typename IRBuilderTy>
Value *EmitGEPOffset(IRBuilderTy *Builder, const DataLayout &DL, User *GEP,
                     bool NoAssumptions = false) {
  GEPOperator *GEPOp = cast<GEPOperator>(GEP);
  Type *IntPtrTy = DL.getIntPtrType(GEP->getType());
  Value *Result = Constant::getNullValue(IntPtrTy);

  // If the GEP is inbounds, we know that none of the addressing operations will
  // overflow in an unsigned sense.
  bool isInBounds = GEPOp->isInBounds() && !NoAssumptions;

  // Build a mask for high order bits.
  unsigned IntPtrWidth = IntPtrTy->getScalarType()->getIntegerBitWidth();
  uint64_t PtrSizeMask = ~0ULL >> (64 - IntPtrWidth);

  gep_type_iterator GTI = gep_type_begin(GEP);
  for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); i != e;
       ++i, ++GTI) {
    Value *Op = *i;
    uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType()) & PtrSizeMask;
    if (Constant *OpC = dyn_cast<Constant>(Op)) {
      if (OpC->isZeroValue())
        continue;

      // Handle a struct index, which adds its field offset to the pointer.
      if (StructType *STy = dyn_cast<StructType>(*GTI)) {
        if (OpC->getType()->isVectorTy())
          OpC = OpC->getSplatValue();

        uint64_t OpValue = cast<ConstantInt>(OpC)->getZExtValue();
        Size = DL.getStructLayout(STy)->getElementOffset(OpValue);

        if (Size)
          Result = Builder->CreateAdd(Result, ConstantInt::get(IntPtrTy, Size),
                                      GEP->getName()+".offs");
        continue;
      }

      Constant *Scale = ConstantInt::get(IntPtrTy, Size);
      Constant *OC = ConstantExpr::getIntegerCast(OpC, IntPtrTy, true /*SExt*/);
      Scale = ConstantExpr::getMul(OC, Scale, isInBounds/*NUW*/);
      // Emit an add instruction.
      Result = Builder->CreateAdd(Result, Scale, GEP->getName()+".offs");
      continue;
    }
    // Convert to correct type.
    if (Op->getType() != IntPtrTy)
      Op = Builder->CreateIntCast(Op, IntPtrTy, true, Op->getName()+".c");
    if (Size != 1) {
      // We'll let instcombine(mul) convert this to a shl if possible.
      Op = Builder->CreateMul(Op, ConstantInt::get(IntPtrTy, Size),
                              GEP->getName()+".idx", isInBounds /*NUW*/);
    }

    // Emit an add instruction.
    Result = Builder->CreateAdd(Op, Result, GEP->getName()+".offs");
  }
  return Result;
}

///===---------------------------------------------------------------------===//
///  Dbg Intrinsic utilities
///

/// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
/// that has an associated llvm.dbg.decl intrinsic.
bool ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
                                     StoreInst *SI, DIBuilder &Builder);

/// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
/// that has an associated llvm.dbg.decl intrinsic.
bool ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
                                     LoadInst *LI, DIBuilder &Builder);

/// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
/// of llvm.dbg.value intrinsics.
bool LowerDbgDeclare(Function &F);

/// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic corresponding to
/// an alloca, if any.
DbgDeclareInst *FindAllocaDbgDeclare(Value *V);

/// \brief Replaces llvm.dbg.declare instruction when an alloca is replaced with
/// a new value.  If Deref is true, tan additional DW_OP_deref is prepended to
/// the expression.
bool replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
                                DIBuilder &Builder, bool Deref);

/// \brief Remove all blocks that can not be reached from the function's entry.
///
/// Returns true if any basic block was removed.
bool removeUnreachableBlocks(Function &F);

/// \brief Combine the metadata of two instructions so that K can replace J
///
/// Metadata not listed as known via KnownIDs is removed
void combineMetadata(Instruction *K, const Instruction *J, ArrayRef<unsigned> KnownIDs);

/// \brief Replace each use of 'From' with 'To' if that use is dominated by 
/// the given edge.  Returns the number of replacements made.
unsigned replaceDominatedUsesWith(Value *From, Value *To, DominatorTree &DT,
                                  const BasicBlockEdge &Edge);
/// \brief Replace each use of 'From' with 'To' if that use is dominated by
/// the given BasicBlock. Returns the number of replacements made.
unsigned replaceDominatedUsesWith(Value *From, Value *To, DominatorTree &DT,
                                  const BasicBlock *BB);
} // End llvm namespace

#endif