mirror of
https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122642 91177308-0d34-0410-b5e6-96231b3b80d8
738 lines
28 KiB
C++
738 lines
28 KiB
C++
//===-- Local.cpp - Functions to perform local transformations ------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This family of functions perform various local transformations to the
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// program.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Constants.h"
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#include "llvm/GlobalAlias.h"
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#include "llvm/GlobalVariable.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Instructions.h"
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#include "llvm/Intrinsics.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/Analysis/ConstantFolding.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/ProfileInfo.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/GetElementPtrTypeIterator.h"
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#include "llvm/Support/MathExtras.h"
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#include "llvm/Support/ValueHandle.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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//===----------------------------------------------------------------------===//
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// Local constant propagation.
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//
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// ConstantFoldTerminator - If a terminator instruction is predicated on a
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// constant value, convert it into an unconditional branch to the constant
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// destination.
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//
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bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
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TerminatorInst *T = BB->getTerminator();
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// Branch - See if we are conditional jumping on constant
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if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
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if (BI->isUnconditional()) return false; // Can't optimize uncond branch
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BasicBlock *Dest1 = BI->getSuccessor(0);
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BasicBlock *Dest2 = BI->getSuccessor(1);
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if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
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// Are we branching on constant?
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// YES. Change to unconditional branch...
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BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
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BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
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//cerr << "Function: " << T->getParent()->getParent()
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// << "\nRemoving branch from " << T->getParent()
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// << "\n\nTo: " << OldDest << endl;
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// Let the basic block know that we are letting go of it. Based on this,
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// it will adjust it's PHI nodes.
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assert(BI->getParent() && "Terminator not inserted in block!");
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OldDest->removePredecessor(BI->getParent());
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// Set the unconditional destination, and change the insn to be an
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// unconditional branch.
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BI->setUnconditionalDest(Destination);
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return true;
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}
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if (Dest2 == Dest1) { // Conditional branch to same location?
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// This branch matches something like this:
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// br bool %cond, label %Dest, label %Dest
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// and changes it into: br label %Dest
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// Let the basic block know that we are letting go of one copy of it.
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assert(BI->getParent() && "Terminator not inserted in block!");
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Dest1->removePredecessor(BI->getParent());
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// Change a conditional branch to unconditional.
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BI->setUnconditionalDest(Dest1);
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return true;
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}
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return false;
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}
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if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
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// If we are switching on a constant, we can convert the switch into a
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// single branch instruction!
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ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
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BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest
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BasicBlock *DefaultDest = TheOnlyDest;
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assert(TheOnlyDest == SI->getDefaultDest() &&
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"Default destination is not successor #0?");
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// Figure out which case it goes to.
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for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
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// Found case matching a constant operand?
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if (SI->getSuccessorValue(i) == CI) {
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TheOnlyDest = SI->getSuccessor(i);
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break;
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}
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// Check to see if this branch is going to the same place as the default
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// dest. If so, eliminate it as an explicit compare.
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if (SI->getSuccessor(i) == DefaultDest) {
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// Remove this entry.
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DefaultDest->removePredecessor(SI->getParent());
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SI->removeCase(i);
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--i; --e; // Don't skip an entry...
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continue;
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}
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// Otherwise, check to see if the switch only branches to one destination.
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// We do this by reseting "TheOnlyDest" to null when we find two non-equal
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// destinations.
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if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0;
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}
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if (CI && !TheOnlyDest) {
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// Branching on a constant, but not any of the cases, go to the default
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// successor.
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TheOnlyDest = SI->getDefaultDest();
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}
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// If we found a single destination that we can fold the switch into, do so
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// now.
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if (TheOnlyDest) {
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// Insert the new branch.
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BranchInst::Create(TheOnlyDest, SI);
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BasicBlock *BB = SI->getParent();
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// Remove entries from PHI nodes which we no longer branch to...
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for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
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// Found case matching a constant operand?
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BasicBlock *Succ = SI->getSuccessor(i);
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if (Succ == TheOnlyDest)
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TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
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else
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Succ->removePredecessor(BB);
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}
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// Delete the old switch.
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BB->getInstList().erase(SI);
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return true;
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}
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if (SI->getNumSuccessors() == 2) {
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// Otherwise, we can fold this switch into a conditional branch
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// instruction if it has only one non-default destination.
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Value *Cond = new ICmpInst(SI, ICmpInst::ICMP_EQ, SI->getCondition(),
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SI->getSuccessorValue(1), "cond");
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// Insert the new branch.
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BranchInst::Create(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI);
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// Delete the old switch.
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SI->eraseFromParent();
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return true;
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}
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return false;
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}
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if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
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// indirectbr blockaddress(@F, @BB) -> br label @BB
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if (BlockAddress *BA =
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dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
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BasicBlock *TheOnlyDest = BA->getBasicBlock();
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// Insert the new branch.
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BranchInst::Create(TheOnlyDest, IBI);
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for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
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if (IBI->getDestination(i) == TheOnlyDest)
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TheOnlyDest = 0;
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else
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IBI->getDestination(i)->removePredecessor(IBI->getParent());
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}
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IBI->eraseFromParent();
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// If we didn't find our destination in the IBI successor list, then we
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// have undefined behavior. Replace the unconditional branch with an
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// 'unreachable' instruction.
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if (TheOnlyDest) {
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BB->getTerminator()->eraseFromParent();
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new UnreachableInst(BB->getContext(), BB);
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}
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return true;
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}
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}
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return false;
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}
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//===----------------------------------------------------------------------===//
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// Local dead code elimination.
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//
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/// isInstructionTriviallyDead - Return true if the result produced by the
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/// instruction is not used, and the instruction has no side effects.
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///
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bool llvm::isInstructionTriviallyDead(Instruction *I) {
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if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
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// We don't want debug info removed by anything this general.
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if (isa<DbgInfoIntrinsic>(I)) return false;
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if (!I->mayHaveSideEffects()) return true;
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// Special case intrinsics that "may have side effects" but can be deleted
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// when dead.
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if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
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// Safe to delete llvm.stacksave if dead.
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if (II->getIntrinsicID() == Intrinsic::stacksave)
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return true;
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return false;
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}
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/// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
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/// trivially dead instruction, delete it. If that makes any of its operands
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/// trivially dead, delete them too, recursively. Return true if any
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/// instructions were deleted.
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bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) {
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Instruction *I = dyn_cast<Instruction>(V);
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if (!I || !I->use_empty() || !isInstructionTriviallyDead(I))
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return false;
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SmallVector<Instruction*, 16> DeadInsts;
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DeadInsts.push_back(I);
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do {
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I = DeadInsts.pop_back_val();
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// Null out all of the instruction's operands to see if any operand becomes
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// dead as we go.
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for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
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Value *OpV = I->getOperand(i);
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I->setOperand(i, 0);
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if (!OpV->use_empty()) continue;
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// If the operand is an instruction that became dead as we nulled out the
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// operand, and if it is 'trivially' dead, delete it in a future loop
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// iteration.
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if (Instruction *OpI = dyn_cast<Instruction>(OpV))
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if (isInstructionTriviallyDead(OpI))
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DeadInsts.push_back(OpI);
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}
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I->eraseFromParent();
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} while (!DeadInsts.empty());
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return true;
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}
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/// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
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/// dead PHI node, due to being a def-use chain of single-use nodes that
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/// either forms a cycle or is terminated by a trivially dead instruction,
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/// delete it. If that makes any of its operands trivially dead, delete them
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/// too, recursively. Return true if the PHI node is actually deleted.
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bool
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llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
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// We can remove a PHI if it is on a cycle in the def-use graph
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// where each node in the cycle has degree one, i.e. only one use,
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// and is an instruction with no side effects.
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if (!PN->hasOneUse())
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return false;
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bool Changed = false;
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SmallPtrSet<PHINode *, 4> PHIs;
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PHIs.insert(PN);
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for (Instruction *J = cast<Instruction>(*PN->use_begin());
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J->hasOneUse() && !J->mayHaveSideEffects();
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J = cast<Instruction>(*J->use_begin()))
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// If we find a PHI more than once, we're on a cycle that
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// won't prove fruitful.
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if (PHINode *JP = dyn_cast<PHINode>(J))
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if (!PHIs.insert(cast<PHINode>(JP))) {
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// Break the cycle and delete the PHI and its operands.
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JP->replaceAllUsesWith(UndefValue::get(JP->getType()));
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(void)RecursivelyDeleteTriviallyDeadInstructions(JP);
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Changed = true;
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break;
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}
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return Changed;
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}
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/// SimplifyInstructionsInBlock - Scan the specified basic block and try to
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/// simplify any instructions in it and recursively delete dead instructions.
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///
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/// This returns true if it changed the code, note that it can delete
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/// instructions in other blocks as well in this block.
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bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) {
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bool MadeChange = false;
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for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
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Instruction *Inst = BI++;
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if (Value *V = SimplifyInstruction(Inst, TD)) {
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WeakVH BIHandle(BI);
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ReplaceAndSimplifyAllUses(Inst, V, TD);
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MadeChange = true;
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if (BIHandle != BI)
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BI = BB->begin();
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continue;
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}
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MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst);
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}
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return MadeChange;
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}
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//===----------------------------------------------------------------------===//
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// Control Flow Graph Restructuring.
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//
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/// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
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/// method is called when we're about to delete Pred as a predecessor of BB. If
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/// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
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///
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/// Unlike the removePredecessor method, this attempts to simplify uses of PHI
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/// nodes that collapse into identity values. For example, if we have:
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/// x = phi(1, 0, 0, 0)
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/// y = and x, z
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///
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/// .. and delete the predecessor corresponding to the '1', this will attempt to
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/// recursively fold the and to 0.
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void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
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TargetData *TD) {
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// This only adjusts blocks with PHI nodes.
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if (!isa<PHINode>(BB->begin()))
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return;
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// Remove the entries for Pred from the PHI nodes in BB, but do not simplify
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// them down. This will leave us with single entry phi nodes and other phis
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// that can be removed.
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BB->removePredecessor(Pred, true);
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WeakVH PhiIt = &BB->front();
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while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
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PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
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Value *PNV = SimplifyInstruction(PN, TD);
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if (PNV == 0) continue;
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// If we're able to simplify the phi to a single value, substitute the new
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// value into all of its uses.
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assert(PNV != PN && "SimplifyInstruction broken!");
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Value *OldPhiIt = PhiIt;
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ReplaceAndSimplifyAllUses(PN, PNV, TD);
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// If recursive simplification ended up deleting the next PHI node we would
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// iterate to, then our iterator is invalid, restart scanning from the top
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// of the block.
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if (PhiIt != OldPhiIt) PhiIt = &BB->front();
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}
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}
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/// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
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/// predecessor is known to have one successor (DestBB!). Eliminate the edge
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/// between them, moving the instructions in the predecessor into DestBB and
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/// deleting the predecessor block.
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///
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void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
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// If BB has single-entry PHI nodes, fold them.
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while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
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Value *NewVal = PN->getIncomingValue(0);
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// Replace self referencing PHI with undef, it must be dead.
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if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
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PN->replaceAllUsesWith(NewVal);
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PN->eraseFromParent();
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}
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BasicBlock *PredBB = DestBB->getSinglePredecessor();
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assert(PredBB && "Block doesn't have a single predecessor!");
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// Splice all the instructions from PredBB to DestBB.
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PredBB->getTerminator()->eraseFromParent();
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DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
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// Zap anything that took the address of DestBB. Not doing this will give the
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// address an invalid value.
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if (DestBB->hasAddressTaken()) {
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BlockAddress *BA = BlockAddress::get(DestBB);
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Constant *Replacement =
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ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
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BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
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BA->getType()));
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BA->destroyConstant();
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}
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// Anything that branched to PredBB now branches to DestBB.
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PredBB->replaceAllUsesWith(DestBB);
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if (P) {
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ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>();
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if (PI) {
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PI->replaceAllUses(PredBB, DestBB);
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PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB));
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}
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}
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// Nuke BB.
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PredBB->eraseFromParent();
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}
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/// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
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/// almost-empty BB ending in an unconditional branch to Succ, into succ.
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///
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/// Assumption: Succ is the single successor for BB.
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///
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static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
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assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
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DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
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<< Succ->getName() << "\n");
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// Shortcut, if there is only a single predecessor it must be BB and merging
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// is always safe
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if (Succ->getSinglePredecessor()) return true;
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// Make a list of the predecessors of BB
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typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
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BlockSet BBPreds(pred_begin(BB), pred_end(BB));
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// Use that list to make another list of common predecessors of BB and Succ
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BlockSet CommonPreds;
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for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
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PI != PE; ++PI) {
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BasicBlock *P = *PI;
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if (BBPreds.count(P))
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CommonPreds.insert(P);
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}
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// Shortcut, if there are no common predecessors, merging is always safe
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if (CommonPreds.empty())
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return true;
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// Look at all the phi nodes in Succ, to see if they present a conflict when
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// merging these blocks
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for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
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PHINode *PN = cast<PHINode>(I);
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// If the incoming value from BB is again a PHINode in
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// BB which has the same incoming value for *PI as PN does, we can
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// merge the phi nodes and then the blocks can still be merged
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PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
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if (BBPN && BBPN->getParent() == BB) {
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for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
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PI != PE; PI++) {
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if (BBPN->getIncomingValueForBlock(*PI)
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!= PN->getIncomingValueForBlock(*PI)) {
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DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
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<< Succ->getName() << " is conflicting with "
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<< BBPN->getName() << " with regard to common predecessor "
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<< (*PI)->getName() << "\n");
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return false;
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}
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}
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} else {
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Value* Val = PN->getIncomingValueForBlock(BB);
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for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
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PI != PE; PI++) {
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// See if the incoming value for the common predecessor is equal to the
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// one for BB, in which case this phi node will not prevent the merging
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// of the block.
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if (Val != PN->getIncomingValueForBlock(*PI)) {
|
|
DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
|
|
<< Succ->getName() << " is conflicting with regard to common "
|
|
<< "predecessor " << (*PI)->getName() << "\n");
|
|
return false;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
/// 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 llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
|
|
assert(BB != &BB->getParent()->getEntryBlock() &&
|
|
"TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
|
|
|
|
// We can't eliminate infinite loops.
|
|
BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
|
|
if (BB == Succ) return false;
|
|
|
|
// Check to see if merging these blocks would cause conflicts for any of the
|
|
// phi nodes in BB or Succ. If not, we can safely merge.
|
|
if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
|
|
|
|
// Check for cases where Succ has multiple predecessors and a PHI node in BB
|
|
// has uses which will not disappear when the PHI nodes are merged. It is
|
|
// possible to handle such cases, but difficult: it requires checking whether
|
|
// BB dominates Succ, which is non-trivial to calculate in the case where
|
|
// Succ has multiple predecessors. Also, it requires checking whether
|
|
// constructing the necessary self-referential PHI node doesn't intoduce any
|
|
// conflicts; this isn't too difficult, but the previous code for doing this
|
|
// was incorrect.
|
|
//
|
|
// Note that if this check finds a live use, BB dominates Succ, so BB is
|
|
// something like a loop pre-header (or rarely, a part of an irreducible CFG);
|
|
// folding the branch isn't profitable in that case anyway.
|
|
if (!Succ->getSinglePredecessor()) {
|
|
BasicBlock::iterator BBI = BB->begin();
|
|
while (isa<PHINode>(*BBI)) {
|
|
for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
|
|
UI != E; ++UI) {
|
|
if (PHINode* PN = dyn_cast<PHINode>(*UI)) {
|
|
if (PN->getIncomingBlock(UI) != BB)
|
|
return false;
|
|
} else {
|
|
return false;
|
|
}
|
|
}
|
|
++BBI;
|
|
}
|
|
}
|
|
|
|
DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
|
|
|
|
if (isa<PHINode>(Succ->begin())) {
|
|
// If there is more than one pred of succ, and there are PHI nodes in
|
|
// the successor, then we need to add incoming edges for the PHI nodes
|
|
//
|
|
const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
|
|
|
|
// Loop over all of the PHI nodes in the successor of BB.
|
|
for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
|
|
PHINode *PN = cast<PHINode>(I);
|
|
Value *OldVal = PN->removeIncomingValue(BB, false);
|
|
assert(OldVal && "No entry in PHI for Pred BB!");
|
|
|
|
// If this incoming value is one of the PHI nodes in BB, the new entries
|
|
// in the PHI node are the entries from the old PHI.
|
|
if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
|
|
PHINode *OldValPN = cast<PHINode>(OldVal);
|
|
for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
|
|
// Note that, since we are merging phi nodes and BB and Succ might
|
|
// have common predecessors, we could end up with a phi node with
|
|
// identical incoming branches. This will be cleaned up later (and
|
|
// will trigger asserts if we try to clean it up now, without also
|
|
// simplifying the corresponding conditional branch).
|
|
PN->addIncoming(OldValPN->getIncomingValue(i),
|
|
OldValPN->getIncomingBlock(i));
|
|
} else {
|
|
// Add an incoming value for each of the new incoming values.
|
|
for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
|
|
PN->addIncoming(OldVal, BBPreds[i]);
|
|
}
|
|
}
|
|
}
|
|
|
|
while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
|
|
if (Succ->getSinglePredecessor()) {
|
|
// BB is the only predecessor of Succ, so Succ will end up with exactly
|
|
// the same predecessors BB had.
|
|
Succ->getInstList().splice(Succ->begin(),
|
|
BB->getInstList(), BB->begin());
|
|
} else {
|
|
// We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
|
|
assert(PN->use_empty() && "There shouldn't be any uses here!");
|
|
PN->eraseFromParent();
|
|
}
|
|
}
|
|
|
|
// Everything that jumped to BB now goes to Succ.
|
|
BB->replaceAllUsesWith(Succ);
|
|
if (!Succ->hasName()) Succ->takeName(BB);
|
|
BB->eraseFromParent(); // Delete the old basic block.
|
|
return true;
|
|
}
|
|
|
|
/// 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 llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
|
|
bool Changed = false;
|
|
|
|
// This implementation doesn't currently consider undef operands
|
|
// specially. Theroetically, two phis which are identical except for
|
|
// one having an undef where the other doesn't could be collapsed.
|
|
|
|
// Map from PHI hash values to PHI nodes. If multiple PHIs have
|
|
// the same hash value, the element is the first PHI in the
|
|
// linked list in CollisionMap.
|
|
DenseMap<uintptr_t, PHINode *> HashMap;
|
|
|
|
// Maintain linked lists of PHI nodes with common hash values.
|
|
DenseMap<PHINode *, PHINode *> CollisionMap;
|
|
|
|
// Examine each PHI.
|
|
for (BasicBlock::iterator I = BB->begin();
|
|
PHINode *PN = dyn_cast<PHINode>(I++); ) {
|
|
// Compute a hash value on the operands. Instcombine will likely have sorted
|
|
// them, which helps expose duplicates, but we have to check all the
|
|
// operands to be safe in case instcombine hasn't run.
|
|
uintptr_t Hash = 0;
|
|
for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
|
|
// This hash algorithm is quite weak as hash functions go, but it seems
|
|
// to do a good enough job for this particular purpose, and is very quick.
|
|
Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
|
|
Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
|
|
}
|
|
// If we've never seen this hash value before, it's a unique PHI.
|
|
std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
|
|
HashMap.insert(std::make_pair(Hash, PN));
|
|
if (Pair.second) continue;
|
|
// Otherwise it's either a duplicate or a hash collision.
|
|
for (PHINode *OtherPN = Pair.first->second; ; ) {
|
|
if (OtherPN->isIdenticalTo(PN)) {
|
|
// A duplicate. Replace this PHI with its duplicate.
|
|
PN->replaceAllUsesWith(OtherPN);
|
|
PN->eraseFromParent();
|
|
Changed = true;
|
|
break;
|
|
}
|
|
// A non-duplicate hash collision.
|
|
DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
|
|
if (I == CollisionMap.end()) {
|
|
// Set this PHI to be the head of the linked list of colliding PHIs.
|
|
PHINode *Old = Pair.first->second;
|
|
Pair.first->second = PN;
|
|
CollisionMap[PN] = Old;
|
|
break;
|
|
}
|
|
// Procede to the next PHI in the list.
|
|
OtherPN = I->second;
|
|
}
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
/// enforceKnownAlignment - If the specified pointer points to an object that
|
|
/// we control, modify the object's alignment to PrefAlign. This isn't
|
|
/// often possible though. If alignment is important, a more reliable approach
|
|
/// is to simply align all global variables and allocation instructions to
|
|
/// their preferred alignment from the beginning.
|
|
///
|
|
static unsigned enforceKnownAlignment(Value *V, unsigned Align,
|
|
unsigned PrefAlign) {
|
|
|
|
User *U = dyn_cast<User>(V);
|
|
if (!U) return Align;
|
|
|
|
switch (Operator::getOpcode(U)) {
|
|
default: break;
|
|
case Instruction::BitCast:
|
|
return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign);
|
|
case Instruction::GetElementPtr: {
|
|
// If all indexes are zero, it is just the alignment of the base pointer.
|
|
bool AllZeroOperands = true;
|
|
for (User::op_iterator i = U->op_begin() + 1, e = U->op_end(); i != e; ++i)
|
|
if (!isa<Constant>(*i) ||
|
|
!cast<Constant>(*i)->isNullValue()) {
|
|
AllZeroOperands = false;
|
|
break;
|
|
}
|
|
|
|
if (AllZeroOperands) {
|
|
// Treat this like a bitcast.
|
|
return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign);
|
|
}
|
|
return Align;
|
|
}
|
|
case Instruction::Alloca: {
|
|
AllocaInst *AI = cast<AllocaInst>(V);
|
|
// If there is a requested alignment and if this is an alloca, round up.
|
|
if (AI->getAlignment() >= PrefAlign)
|
|
return AI->getAlignment();
|
|
AI->setAlignment(PrefAlign);
|
|
return PrefAlign;
|
|
}
|
|
}
|
|
|
|
if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
|
|
// If there is a large requested alignment and we can, bump up the alignment
|
|
// of the global.
|
|
if (GV->isDeclaration()) return Align;
|
|
|
|
if (GV->getAlignment() >= PrefAlign)
|
|
return GV->getAlignment();
|
|
// We can only increase the alignment of the global if it has no alignment
|
|
// specified or if it is not assigned a section. If it is assigned a
|
|
// section, the global could be densely packed with other objects in the
|
|
// section, increasing the alignment could cause padding issues.
|
|
if (!GV->hasSection() || GV->getAlignment() == 0)
|
|
GV->setAlignment(PrefAlign);
|
|
return GV->getAlignment();
|
|
}
|
|
|
|
return Align;
|
|
}
|
|
|
|
/// 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 llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
|
|
const TargetData *TD) {
|
|
assert(V->getType()->isPointerTy() &&
|
|
"getOrEnforceKnownAlignment expects a pointer!");
|
|
unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64;
|
|
APInt Mask = APInt::getAllOnesValue(BitWidth);
|
|
APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
|
|
ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD);
|
|
unsigned TrailZ = KnownZero.countTrailingOnes();
|
|
|
|
// Avoid trouble with rediculously large TrailZ values, such as
|
|
// those computed from a null pointer.
|
|
TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
|
|
|
|
unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
|
|
|
|
// LLVM doesn't support alignments larger than this currently.
|
|
Align = std::min(Align, +Value::MaximumAlignment);
|
|
|
|
if (PrefAlign > Align)
|
|
Align = enforceKnownAlignment(V, Align, PrefAlign);
|
|
|
|
// We don't need to make any adjustment.
|
|
return Align;
|
|
}
|
|
|