Import LLVM, at r72732.

1 files changed, 338 insertions, 0 deletions

diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp
new file mode 100644
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+++ b/lib/Transforms/Utils/Local.cpp
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+//===-- Local.cpp - Functions to perform local transformations ------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Constants.h"
+#include "llvm/GlobalVariable.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Instructions.h"
+#include "llvm/Intrinsics.h"
+#include "llvm/IntrinsicInst.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Analysis/DebugInfo.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Support/GetElementPtrTypeIterator.h"
+#include "llvm/Support/MathExtras.h"
+using namespace llvm;
+
+//===----------------------------------------------------------------------===//
+//  Local constant propagation.
+//
+
+// ConstantFoldTerminator - If a terminator instruction is predicated on a
+// constant value, convert it into an unconditional branch to the constant
+// destination.
+//
+bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
+  TerminatorInst *T = BB->getTerminator();
+
+  // Branch - See if we are conditional jumping on constant
+  if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
+    if (BI->isUnconditional()) return false;  // Can't optimize uncond branch
+    BasicBlock *Dest1 = BI->getSuccessor(0);
+    BasicBlock *Dest2 = BI->getSuccessor(1);
+
+    if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
+      // Are we branching on constant?
+      // YES.  Change to unconditional branch...
+      BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
+      BasicBlock *OldDest     = Cond->getZExtValue() ? Dest2 : Dest1;
+
+      //cerr << "Function: " << T->getParent()->getParent()
+      //     << "\nRemoving branch from " << T->getParent()
+      //     << "\n\nTo: " << OldDest << endl;
+
+      // Let the basic block know that we are letting go of it.  Based on this,
+      // it will adjust it's PHI nodes.
+      assert(BI->getParent() && "Terminator not inserted in block!");
+      OldDest->removePredecessor(BI->getParent());
+
+      // Set the unconditional destination, and change the insn to be an
+      // unconditional branch.
+      BI->setUnconditionalDest(Destination);
+      return true;
+    } else if (Dest2 == Dest1) {       // Conditional branch to same location?
+      // This branch matches something like this:
+      //     br bool %cond, label %Dest, label %Dest
+      // and changes it into:  br label %Dest
+
+      // Let the basic block know that we are letting go of one copy of it.
+      assert(BI->getParent() && "Terminator not inserted in block!");
+      Dest1->removePredecessor(BI->getParent());
+
+      // Change a conditional branch to unconditional.
+      BI->setUnconditionalDest(Dest1);
+      return true;
+    }
+  } else if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
+    // If we are switching on a constant, we can convert the switch into a
+    // single branch instruction!
+    ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
+    BasicBlock *TheOnlyDest = SI->getSuccessor(0);  // The default dest
+    BasicBlock *DefaultDest = TheOnlyDest;
+    assert(TheOnlyDest == SI->getDefaultDest() &&
+           "Default destination is not successor #0?");
+
+    // Figure out which case it goes to...
+    for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
+      // Found case matching a constant operand?
+      if (SI->getSuccessorValue(i) == CI) {
+        TheOnlyDest = SI->getSuccessor(i);
+        break;
+      }
+
+      // Check to see if this branch is going to the same place as the default
+      // dest.  If so, eliminate it as an explicit compare.
+      if (SI->getSuccessor(i) == DefaultDest) {
+        // Remove this entry...
+        DefaultDest->removePredecessor(SI->getParent());
+        SI->removeCase(i);
+        --i; --e;  // Don't skip an entry...
+        continue;
+      }
+
+      // Otherwise, check to see if the switch only branches to one destination.
+      // We do this by reseting "TheOnlyDest" to null when we find two non-equal
+      // destinations.
+      if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0;
+    }
+
+    if (CI && !TheOnlyDest) {
+      // Branching on a constant, but not any of the cases, go to the default
+      // successor.
+      TheOnlyDest = SI->getDefaultDest();
+    }
+
+    // If we found a single destination that we can fold the switch into, do so
+    // now.
+    if (TheOnlyDest) {
+      // Insert the new branch..
+      BranchInst::Create(TheOnlyDest, SI);
+      BasicBlock *BB = SI->getParent();
+
+      // Remove entries from PHI nodes which we no longer branch to...
+      for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
+        // Found case matching a constant operand?
+        BasicBlock *Succ = SI->getSuccessor(i);
+        if (Succ == TheOnlyDest)
+          TheOnlyDest = 0;  // Don't modify the first branch to TheOnlyDest
+        else
+          Succ->removePredecessor(BB);
+      }
+
+      // Delete the old switch...
+      BB->getInstList().erase(SI);
+      return true;
+    } else if (SI->getNumSuccessors() == 2) {
+      // Otherwise, we can fold this switch into a conditional branch
+      // instruction if it has only one non-default destination.
+      Value *Cond = new ICmpInst(ICmpInst::ICMP_EQ, SI->getCondition(),
+                                 SI->getSuccessorValue(1), "cond", SI);
+      // Insert the new branch...
+      BranchInst::Create(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI);
+
+      // Delete the old switch...
+      SI->eraseFromParent();
+      return true;
+    }
+  }
+  return false;
+}
+
+
+//===----------------------------------------------------------------------===//
+//  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 llvm::isInstructionTriviallyDead(Instruction *I) {
+  if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
+
+  // We don't want debug info removed by anything this general.
+  if (isa<DbgInfoIntrinsic>(I)) return false;
+
+  if (!I->mayHaveSideEffects()) return true;
+
+  // Special case intrinsics that "may have side effects" but can be deleted
+  // when dead.
+  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
+    // Safe to delete llvm.stacksave if dead.
+    if (II->getIntrinsicID() == Intrinsic::stacksave)
+      return true;
+  return false;
+}
+
+/// 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.
+void llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) {
+  Instruction *I = dyn_cast<Instruction>(V);
+  if (!I || !I->use_empty() || !isInstructionTriviallyDead(I))
+    return;
+  
+  SmallVector<Instruction*, 16> DeadInsts;
+  DeadInsts.push_back(I);
+  
+  while (!DeadInsts.empty()) {
+    I = DeadInsts.pop_back_val();
+
+    // Null out all of the instruction's operands to see if any operand becomes
+    // dead as we go.
+    for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
+      Value *OpV = I->getOperand(i);
+      I->setOperand(i, 0);
+      
+      if (!OpV->use_empty()) continue;
+    
+      // If the operand is an instruction that became dead as we nulled out the
+      // operand, and if it is 'trivially' dead, delete it in a future loop
+      // iteration.
+      if (Instruction *OpI = dyn_cast<Instruction>(OpV))
+        if (isInstructionTriviallyDead(OpI))
+          DeadInsts.push_back(OpI);
+    }
+    
+    I->eraseFromParent();
+  }
+}
+
+/// 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.
+void
+llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
+
+  // We can remove a PHI if it is on a cycle in the def-use graph
+  // where each node in the cycle has degree one, i.e. only one use,
+  // and is an instruction with no side effects.
+  if (!PN->hasOneUse())
+    return;
+
+  SmallPtrSet<PHINode *, 4> PHIs;
+  PHIs.insert(PN);
+  for (Instruction *J = cast<Instruction>(*PN->use_begin());
+       J->hasOneUse() && !J->mayHaveSideEffects();
+       J = cast<Instruction>(*J->use_begin()))
+    // If we find a PHI more than once, we're on a cycle that
+    // won't prove fruitful.
+    if (PHINode *JP = dyn_cast<PHINode>(J))
+      if (!PHIs.insert(cast<PHINode>(JP))) {
+        // Break the cycle and delete the PHI and its operands.
+        JP->replaceAllUsesWith(UndefValue::get(JP->getType()));
+        RecursivelyDeleteTriviallyDeadInstructions(JP);
+        break;
+      }
+}
+
+//===----------------------------------------------------------------------===//
+//  Control Flow Graph Restructuring...
+//
+
+/// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
+/// predecessor is known to have one successor (DestBB!).  Eliminate the edge
+/// between them, moving the instructions in the predecessor into DestBB and
+/// deleting the predecessor block.
+///
+void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB) {
+  // If BB has single-entry PHI nodes, fold them.
+  while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
+    Value *NewVal = PN->getIncomingValue(0);
+    // Replace self referencing PHI with undef, it must be dead.
+    if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
+    PN->replaceAllUsesWith(NewVal);
+    PN->eraseFromParent();
+  }
+  
+  BasicBlock *PredBB = DestBB->getSinglePredecessor();
+  assert(PredBB && "Block doesn't have a single predecessor!");
+  
+  // Splice all the instructions from PredBB to DestBB.
+  PredBB->getTerminator()->eraseFromParent();
+  DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
+  
+  // Anything that branched to PredBB now branches to DestBB.
+  PredBB->replaceAllUsesWith(DestBB);
+  
+  // Nuke BB.
+  PredBB->eraseFromParent();
+}
+
+/// OnlyUsedByDbgIntrinsics - Return true if the instruction I is only used
+/// by DbgIntrinsics. If DbgInUses is specified then the vector is filled 
+/// with the DbgInfoIntrinsic that use the instruction I.
+bool llvm::OnlyUsedByDbgInfoIntrinsics(Instruction *I, 
+                               SmallVectorImpl<DbgInfoIntrinsic *> *DbgInUses) {
+  if (DbgInUses)
+    DbgInUses->clear();
+
+  for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); UI != UE; 
+       ++UI) {
+    if (DbgInfoIntrinsic *DI = dyn_cast<DbgInfoIntrinsic>(*UI)) {
+      if (DbgInUses)
+        DbgInUses->push_back(DI);
+    } else {
+      if (DbgInUses)
+        DbgInUses->clear();
+      return false;
+    }
+  }
+  return true;
+}
+
+/// UserIsDebugInfo - Return true if U is a constant expr used by 
+/// llvm.dbg.variable or llvm.dbg.global_variable
+bool llvm::UserIsDebugInfo(User *U) {
+  ConstantExpr *CE = dyn_cast<ConstantExpr>(U);
+
+  if (!CE || CE->getNumUses() != 1)
+    return false;
+
+  Constant *Init = dyn_cast<Constant>(CE->use_back());
+  if (!Init || Init->getNumUses() != 1)
+    return false;
+
+  GlobalVariable *GV = dyn_cast<GlobalVariable>(Init->use_back());
+  if (!GV || !GV->hasInitializer() || GV->getInitializer() != Init)
+    return false;
+
+  DIVariable DV(GV);
+  if (!DV.isNull()) 
+    return true; // User is llvm.dbg.variable
+
+  DIGlobalVariable DGV(GV);
+  if (!DGV.isNull())
+    return true; // User is llvm.dbg.global_variable
+
+  return false;
+}
+
+/// RemoveDbgInfoUser - Remove an User which is representing debug info.
+void llvm::RemoveDbgInfoUser(User *U) {
+  assert (UserIsDebugInfo(U) && "Unexpected User!");
+  ConstantExpr *CE = cast<ConstantExpr>(U);
+  while (!CE->use_empty()) {
+    Constant *C = cast<Constant>(CE->use_back());
+    while (!C->use_empty()) {
+      GlobalVariable *GV = cast<GlobalVariable>(C->use_back());
+      GV->eraseFromParent();
+    }
+    C->destroyConstant();
+  }
+  CE->destroyConstant();
+}