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257 lines
8.8 KiB
257 lines
8.8 KiB
4 months ago
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//===- PPCBoolRetToInt.cpp - Convert bool literals to i32 if they are returned ==//
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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 file implements converting i1 values to i32 if they could be more
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// profitably allocated as GPRs rather than CRs. This pass will become totally
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// unnecessary if Register Bank Allocation and Global Instruction Selection ever
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// go upstream.
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//
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// Presently, the pass converts i1 Constants, and Arguments to i32 if the
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// transitive closure of their uses includes only PHINodes, CallInsts, and
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// ReturnInsts. The rational is that arguments are generally passed and returned
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// in GPRs rather than CRs, so casting them to i32 at the LLVM IR level will
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// actually save casts at the Machine Instruction level.
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//
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// It might be useful to expand this pass to add bit-wise operations to the list
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// of safe transitive closure types. Also, we miss some opportunities when LLVM
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// represents logical AND and OR operations with control flow rather than data
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// flow. For example by lowering the expression: return (A && B && C)
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//
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// as: return A ? true : B && C.
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//
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// There's code in SimplifyCFG that code be used to turn control flow in data
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// flow using SelectInsts. Selects are slow on some architectures (P7/P8), so
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// this probably isn't good in general, but for the special case of i1, the
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// Selects could be further lowered to bit operations that are fast everywhere.
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//
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//===----------------------------------------------------------------------===//
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#include "PPC.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Pass.h"
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using namespace llvm;
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namespace {
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#define DEBUG_TYPE "bool-ret-to-int"
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STATISTIC(NumBoolRetPromotion,
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"Number of times a bool feeding a RetInst was promoted to an int");
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STATISTIC(NumBoolCallPromotion,
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"Number of times a bool feeding a CallInst was promoted to an int");
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STATISTIC(NumBoolToIntPromotion,
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"Total number of times a bool was promoted to an int");
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class PPCBoolRetToInt : public FunctionPass {
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static SmallPtrSet<Value *, 8> findAllDefs(Value *V) {
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SmallPtrSet<Value *, 8> Defs;
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SmallVector<Value *, 8> WorkList;
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WorkList.push_back(V);
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Defs.insert(V);
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while (!WorkList.empty()) {
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Value *Curr = WorkList.back();
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WorkList.pop_back();
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if (User *CurrUser = dyn_cast<User>(Curr))
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for (auto &Op : CurrUser->operands())
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if (Defs.insert(Op).second)
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WorkList.push_back(Op);
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}
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return Defs;
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}
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// Translate a i1 value to an equivalent i32 value:
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static Value *translate(Value *V) {
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Type *Int32Ty = Type::getInt32Ty(V->getContext());
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if (Constant *C = dyn_cast<Constant>(V))
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return ConstantExpr::getZExt(C, Int32Ty);
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if (PHINode *P = dyn_cast<PHINode>(V)) {
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// Temporarily set the operands to 0. We'll fix this later in
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// runOnUse.
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Value *Zero = Constant::getNullValue(Int32Ty);
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PHINode *Q =
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PHINode::Create(Int32Ty, P->getNumIncomingValues(), P->getName(), P);
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for (unsigned i = 0; i < P->getNumOperands(); ++i)
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Q->addIncoming(Zero, P->getIncomingBlock(i));
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return Q;
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}
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Argument *A = dyn_cast<Argument>(V);
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Instruction *I = dyn_cast<Instruction>(V);
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assert((A || I) && "Unknown value type");
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auto InstPt =
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A ? &*A->getParent()->getEntryBlock().begin() : I->getNextNode();
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return new ZExtInst(V, Int32Ty, "", InstPt);
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}
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typedef SmallPtrSet<const PHINode *, 8> PHINodeSet;
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// A PHINode is Promotable if:
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// 1. Its type is i1 AND
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// 2. All of its uses are ReturnInt, CallInst, PHINode, or DbgInfoIntrinsic
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// AND
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// 3. All of its operands are Constant or Argument or
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// CallInst or PHINode AND
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// 4. All of its PHINode uses are Promotable AND
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// 5. All of its PHINode operands are Promotable
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static PHINodeSet getPromotablePHINodes(const Function &F) {
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PHINodeSet Promotable;
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// Condition 1
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for (auto &BB : F)
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for (auto &I : BB)
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if (const PHINode *P = dyn_cast<PHINode>(&I))
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if (P->getType()->isIntegerTy(1))
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Promotable.insert(P);
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SmallVector<const PHINode *, 8> ToRemove;
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for (const PHINode *P : Promotable) {
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// Condition 2 and 3
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auto IsValidUser = [] (const Value *V) -> bool {
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return isa<ReturnInst>(V) || isa<CallInst>(V) || isa<PHINode>(V) ||
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isa<DbgInfoIntrinsic>(V);
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};
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auto IsValidOperand = [] (const Value *V) -> bool {
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return isa<Constant>(V) || isa<Argument>(V) || isa<CallInst>(V) ||
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isa<PHINode>(V);
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};
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const auto &Users = P->users();
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const auto &Operands = P->operands();
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if (!std::all_of(Users.begin(), Users.end(), IsValidUser) ||
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!std::all_of(Operands.begin(), Operands.end(), IsValidOperand))
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ToRemove.push_back(P);
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}
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// Iterate to convergence
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auto IsPromotable = [&Promotable] (const Value *V) -> bool {
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const PHINode *Phi = dyn_cast<PHINode>(V);
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return !Phi || Promotable.count(Phi);
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};
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while (!ToRemove.empty()) {
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for (auto &User : ToRemove)
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Promotable.erase(User);
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ToRemove.clear();
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for (const PHINode *P : Promotable) {
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// Condition 4 and 5
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const auto &Users = P->users();
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const auto &Operands = P->operands();
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if (!std::all_of(Users.begin(), Users.end(), IsPromotable) ||
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!std::all_of(Operands.begin(), Operands.end(), IsPromotable))
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ToRemove.push_back(P);
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}
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}
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return Promotable;
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}
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typedef DenseMap<Value *, Value *> B2IMap;
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public:
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static char ID;
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PPCBoolRetToInt() : FunctionPass(ID) {
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initializePPCBoolRetToIntPass(*PassRegistry::getPassRegistry());
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}
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bool runOnFunction(Function &F) {
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if (skipFunction(F))
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return false;
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PHINodeSet PromotablePHINodes = getPromotablePHINodes(F);
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B2IMap Bool2IntMap;
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bool Changed = false;
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for (auto &BB : F) {
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for (auto &I : BB) {
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if (ReturnInst *R = dyn_cast<ReturnInst>(&I))
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if (F.getReturnType()->isIntegerTy(1))
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Changed |=
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runOnUse(R->getOperandUse(0), PromotablePHINodes, Bool2IntMap);
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if (CallInst *CI = dyn_cast<CallInst>(&I))
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for (auto &U : CI->operands())
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if (U->getType()->isIntegerTy(1))
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Changed |= runOnUse(U, PromotablePHINodes, Bool2IntMap);
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}
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}
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return Changed;
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}
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static bool runOnUse(Use &U, const PHINodeSet &PromotablePHINodes,
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B2IMap &BoolToIntMap) {
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auto Defs = findAllDefs(U);
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// If the values are all Constants or Arguments, don't bother
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if (!std::any_of(Defs.begin(), Defs.end(), isa<Instruction, Value *>))
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return false;
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// Presently, we only know how to handle PHINode, Constant, and Arguments.
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// Potentially, bitwise operations (AND, OR, XOR, NOT) and sign extension
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// could also be handled in the future.
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for (Value *V : Defs)
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if (!isa<PHINode>(V) && !isa<Constant>(V) && !isa<Argument>(V))
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return false;
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for (Value *V : Defs)
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if (const PHINode *P = dyn_cast<PHINode>(V))
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if (!PromotablePHINodes.count(P))
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return false;
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if (isa<ReturnInst>(U.getUser()))
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++NumBoolRetPromotion;
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if (isa<CallInst>(U.getUser()))
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++NumBoolCallPromotion;
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++NumBoolToIntPromotion;
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for (Value *V : Defs)
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if (!BoolToIntMap.count(V))
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BoolToIntMap[V] = translate(V);
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// Replace the operands of the translated instructions. There were set to
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// zero in the translate function.
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for (auto &Pair : BoolToIntMap) {
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User *First = dyn_cast<User>(Pair.first);
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User *Second = dyn_cast<User>(Pair.second);
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assert((!First || Second) && "translated from user to non-user!?");
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if (First)
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for (unsigned i = 0; i < First->getNumOperands(); ++i)
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Second->setOperand(i, BoolToIntMap[First->getOperand(i)]);
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}
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Value *IntRetVal = BoolToIntMap[U];
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Type *Int1Ty = Type::getInt1Ty(U->getContext());
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Instruction *I = cast<Instruction>(U.getUser());
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Value *BackToBool = new TruncInst(IntRetVal, Int1Ty, "backToBool", I);
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U.set(BackToBool);
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return true;
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}
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void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addPreserved<DominatorTreeWrapperPass>();
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FunctionPass::getAnalysisUsage(AU);
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}
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};
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}
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char PPCBoolRetToInt::ID = 0;
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INITIALIZE_PASS(PPCBoolRetToInt, "bool-ret-to-int",
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"Convert i1 constants to i32 if they are returned",
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false, false)
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FunctionPass *llvm::createPPCBoolRetToIntPass() { return new PPCBoolRetToInt(); }
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