542 lines
18 KiB
C++
542 lines
18 KiB
C++
//===- Float2Int.cpp - Demote floating point ops to work on integers ------===//
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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 the Float2Int pass, which aims to demote floating
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// point operations to work on integers, where that is losslessly possible.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "float2int"
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#include "llvm/Transforms/Scalar/Float2Int.h"
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#include "llvm/ADT/APInt.h"
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#include "llvm/ADT/APSInt.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/GlobalsModRef.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/InstIterator.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Scalar.h"
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#include <deque>
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#include <functional> // For std::function
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using namespace llvm;
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// The algorithm is simple. Start at instructions that convert from the
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// float to the int domain: fptoui, fptosi and fcmp. Walk up the def-use
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// graph, using an equivalence datastructure to unify graphs that interfere.
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//
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// Mappable instructions are those with an integer corrollary that, given
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// integer domain inputs, produce an integer output; fadd, for example.
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//
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// If a non-mappable instruction is seen, this entire def-use graph is marked
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// as non-transformable. If we see an instruction that converts from the
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// integer domain to FP domain (uitofp,sitofp), we terminate our walk.
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/// The largest integer type worth dealing with.
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static cl::opt<unsigned>
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MaxIntegerBW("float2int-max-integer-bw", cl::init(64), cl::Hidden,
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cl::desc("Max integer bitwidth to consider in float2int"
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"(default=64)"));
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namespace {
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struct Float2IntLegacyPass : public FunctionPass {
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static char ID; // Pass identification, replacement for typeid
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Float2IntLegacyPass() : FunctionPass(ID) {
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initializeFloat2IntLegacyPassPass(*PassRegistry::getPassRegistry());
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}
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bool runOnFunction(Function &F) override {
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if (skipFunction(F))
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return false;
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return Impl.runImpl(F);
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesCFG();
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AU.addPreserved<GlobalsAAWrapperPass>();
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}
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private:
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Float2IntPass Impl;
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};
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}
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char Float2IntLegacyPass::ID = 0;
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INITIALIZE_PASS(Float2IntLegacyPass, "float2int", "Float to int", false, false)
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// Given a FCmp predicate, return a matching ICmp predicate if one
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// exists, otherwise return BAD_ICMP_PREDICATE.
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static CmpInst::Predicate mapFCmpPred(CmpInst::Predicate P) {
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switch (P) {
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case CmpInst::FCMP_OEQ:
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case CmpInst::FCMP_UEQ:
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return CmpInst::ICMP_EQ;
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case CmpInst::FCMP_OGT:
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case CmpInst::FCMP_UGT:
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return CmpInst::ICMP_SGT;
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case CmpInst::FCMP_OGE:
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case CmpInst::FCMP_UGE:
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return CmpInst::ICMP_SGE;
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case CmpInst::FCMP_OLT:
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case CmpInst::FCMP_ULT:
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return CmpInst::ICMP_SLT;
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case CmpInst::FCMP_OLE:
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case CmpInst::FCMP_ULE:
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return CmpInst::ICMP_SLE;
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case CmpInst::FCMP_ONE:
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case CmpInst::FCMP_UNE:
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return CmpInst::ICMP_NE;
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default:
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return CmpInst::BAD_ICMP_PREDICATE;
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}
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}
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// Given a floating point binary operator, return the matching
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// integer version.
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static Instruction::BinaryOps mapBinOpcode(unsigned Opcode) {
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switch (Opcode) {
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default: llvm_unreachable("Unhandled opcode!");
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case Instruction::FAdd: return Instruction::Add;
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case Instruction::FSub: return Instruction::Sub;
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case Instruction::FMul: return Instruction::Mul;
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}
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}
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// Find the roots - instructions that convert from the FP domain to
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// integer domain.
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void Float2IntPass::findRoots(Function &F, SmallPtrSet<Instruction*,8> &Roots) {
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for (auto &I : instructions(F)) {
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if (isa<VectorType>(I.getType()))
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continue;
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switch (I.getOpcode()) {
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default: break;
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case Instruction::FPToUI:
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case Instruction::FPToSI:
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Roots.insert(&I);
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break;
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case Instruction::FCmp:
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if (mapFCmpPred(cast<CmpInst>(&I)->getPredicate()) !=
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CmpInst::BAD_ICMP_PREDICATE)
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Roots.insert(&I);
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break;
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}
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}
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}
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// Helper - mark I as having been traversed, having range R.
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ConstantRange Float2IntPass::seen(Instruction *I, ConstantRange R) {
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DEBUG(dbgs() << "F2I: " << *I << ":" << R << "\n");
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if (SeenInsts.find(I) != SeenInsts.end())
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SeenInsts.find(I)->second = R;
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else
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SeenInsts.insert(std::make_pair(I, R));
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return R;
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}
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// Helper - get a range representing a poison value.
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ConstantRange Float2IntPass::badRange() {
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return ConstantRange(MaxIntegerBW + 1, true);
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}
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ConstantRange Float2IntPass::unknownRange() {
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return ConstantRange(MaxIntegerBW + 1, false);
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}
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ConstantRange Float2IntPass::validateRange(ConstantRange R) {
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if (R.getBitWidth() > MaxIntegerBW + 1)
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return badRange();
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return R;
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}
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// The most obvious way to structure the search is a depth-first, eager
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// search from each root. However, that require direct recursion and so
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// can only handle small instruction sequences. Instead, we split the search
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// up into two phases:
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// - walkBackwards: A breadth-first walk of the use-def graph starting from
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// the roots. Populate "SeenInsts" with interesting
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// instructions and poison values if they're obvious and
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// cheap to compute. Calculate the equivalance set structure
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// while we're here too.
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// - walkForwards: Iterate over SeenInsts in reverse order, so we visit
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// defs before their uses. Calculate the real range info.
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// Breadth-first walk of the use-def graph; determine the set of nodes
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// we care about and eagerly determine if some of them are poisonous.
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void Float2IntPass::walkBackwards(const SmallPtrSetImpl<Instruction*> &Roots) {
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std::deque<Instruction*> Worklist(Roots.begin(), Roots.end());
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while (!Worklist.empty()) {
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Instruction *I = Worklist.back();
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Worklist.pop_back();
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if (SeenInsts.find(I) != SeenInsts.end())
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// Seen already.
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continue;
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switch (I->getOpcode()) {
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// FIXME: Handle select and phi nodes.
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default:
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// Path terminated uncleanly.
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seen(I, badRange());
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break;
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case Instruction::UIToFP: {
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// Path terminated cleanly.
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unsigned BW = I->getOperand(0)->getType()->getPrimitiveSizeInBits();
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APInt Min = APInt::getMinValue(BW).zextOrSelf(MaxIntegerBW+1);
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APInt Max = APInt::getMaxValue(BW).zextOrSelf(MaxIntegerBW+1);
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seen(I, validateRange(ConstantRange(Min, Max)));
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continue;
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}
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case Instruction::SIToFP: {
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// Path terminated cleanly.
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unsigned BW = I->getOperand(0)->getType()->getPrimitiveSizeInBits();
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APInt SMin = APInt::getSignedMinValue(BW).sextOrSelf(MaxIntegerBW+1);
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APInt SMax = APInt::getSignedMaxValue(BW).sextOrSelf(MaxIntegerBW+1);
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seen(I, validateRange(ConstantRange(SMin, SMax)));
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continue;
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}
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case Instruction::FAdd:
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case Instruction::FSub:
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case Instruction::FMul:
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case Instruction::FPToUI:
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case Instruction::FPToSI:
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case Instruction::FCmp:
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seen(I, unknownRange());
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break;
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}
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for (Value *O : I->operands()) {
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if (Instruction *OI = dyn_cast<Instruction>(O)) {
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// Unify def-use chains if they interfere.
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ECs.unionSets(I, OI);
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if (SeenInsts.find(I)->second != badRange())
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Worklist.push_back(OI);
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} else if (!isa<ConstantFP>(O)) {
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// Not an instruction or ConstantFP? we can't do anything.
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seen(I, badRange());
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}
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}
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}
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}
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// Walk forwards down the list of seen instructions, so we visit defs before
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// uses.
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void Float2IntPass::walkForwards() {
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for (auto &It : reverse(SeenInsts)) {
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if (It.second != unknownRange())
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continue;
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Instruction *I = It.first;
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std::function<ConstantRange(ArrayRef<ConstantRange>)> Op;
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switch (I->getOpcode()) {
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// FIXME: Handle select and phi nodes.
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default:
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case Instruction::UIToFP:
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case Instruction::SIToFP:
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llvm_unreachable("Should have been handled in walkForwards!");
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case Instruction::FAdd:
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Op = [](ArrayRef<ConstantRange> Ops) {
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assert(Ops.size() == 2 && "FAdd is a binary operator!");
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return Ops[0].add(Ops[1]);
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};
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break;
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case Instruction::FSub:
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Op = [](ArrayRef<ConstantRange> Ops) {
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assert(Ops.size() == 2 && "FSub is a binary operator!");
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return Ops[0].sub(Ops[1]);
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};
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break;
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case Instruction::FMul:
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Op = [](ArrayRef<ConstantRange> Ops) {
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assert(Ops.size() == 2 && "FMul is a binary operator!");
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return Ops[0].multiply(Ops[1]);
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};
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break;
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//
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// Root-only instructions - we'll only see these if they're the
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// first node in a walk.
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//
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case Instruction::FPToUI:
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case Instruction::FPToSI:
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Op = [](ArrayRef<ConstantRange> Ops) {
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assert(Ops.size() == 1 && "FPTo[US]I is a unary operator!");
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return Ops[0];
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};
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break;
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case Instruction::FCmp:
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Op = [](ArrayRef<ConstantRange> Ops) {
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assert(Ops.size() == 2 && "FCmp is a binary operator!");
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return Ops[0].unionWith(Ops[1]);
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};
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break;
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}
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bool Abort = false;
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SmallVector<ConstantRange,4> OpRanges;
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for (Value *O : I->operands()) {
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if (Instruction *OI = dyn_cast<Instruction>(O)) {
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assert(SeenInsts.find(OI) != SeenInsts.end() &&
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"def not seen before use!");
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OpRanges.push_back(SeenInsts.find(OI)->second);
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} else if (ConstantFP *CF = dyn_cast<ConstantFP>(O)) {
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// Work out if the floating point number can be losslessly represented
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// as an integer.
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// APFloat::convertToInteger(&Exact) purports to do what we want, but
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// the exactness can be too precise. For example, negative zero can
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// never be exactly converted to an integer.
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//
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// Instead, we ask APFloat to round itself to an integral value - this
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// preserves sign-of-zero - then compare the result with the original.
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//
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const APFloat &F = CF->getValueAPF();
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// First, weed out obviously incorrect values. Non-finite numbers
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// can't be represented and neither can negative zero, unless
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// we're in fast math mode.
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if (!F.isFinite() ||
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(F.isZero() && F.isNegative() && isa<FPMathOperator>(I) &&
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!I->hasNoSignedZeros())) {
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seen(I, badRange());
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Abort = true;
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break;
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}
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APFloat NewF = F;
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auto Res = NewF.roundToIntegral(APFloat::rmNearestTiesToEven);
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if (Res != APFloat::opOK || NewF.compare(F) != APFloat::cmpEqual) {
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seen(I, badRange());
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Abort = true;
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break;
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}
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// OK, it's representable. Now get it.
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APSInt Int(MaxIntegerBW+1, false);
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bool Exact;
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CF->getValueAPF().convertToInteger(Int,
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APFloat::rmNearestTiesToEven,
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&Exact);
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OpRanges.push_back(ConstantRange(Int));
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} else {
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llvm_unreachable("Should have already marked this as badRange!");
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}
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}
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// Reduce the operands' ranges to a single range and return.
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if (!Abort)
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seen(I, Op(OpRanges));
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}
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}
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// If there is a valid transform to be done, do it.
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bool Float2IntPass::validateAndTransform() {
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bool MadeChange = false;
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// Iterate over every disjoint partition of the def-use graph.
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for (auto It = ECs.begin(), E = ECs.end(); It != E; ++It) {
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ConstantRange R(MaxIntegerBW + 1, false);
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bool Fail = false;
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Type *ConvertedToTy = nullptr;
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// For every member of the partition, union all the ranges together.
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for (auto MI = ECs.member_begin(It), ME = ECs.member_end();
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MI != ME; ++MI) {
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Instruction *I = *MI;
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auto SeenI = SeenInsts.find(I);
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if (SeenI == SeenInsts.end())
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continue;
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R = R.unionWith(SeenI->second);
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// We need to ensure I has no users that have not been seen.
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// If it does, transformation would be illegal.
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//
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// Don't count the roots, as they terminate the graphs.
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if (Roots.count(I) == 0) {
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// Set the type of the conversion while we're here.
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if (!ConvertedToTy)
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ConvertedToTy = I->getType();
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for (User *U : I->users()) {
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Instruction *UI = dyn_cast<Instruction>(U);
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if (!UI || SeenInsts.find(UI) == SeenInsts.end()) {
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DEBUG(dbgs() << "F2I: Failing because of " << *U << "\n");
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Fail = true;
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break;
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}
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}
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}
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if (Fail)
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break;
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}
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// If the set was empty, or we failed, or the range is poisonous,
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// bail out.
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if (ECs.member_begin(It) == ECs.member_end() || Fail ||
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R.isFullSet() || R.isSignWrappedSet())
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continue;
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assert(ConvertedToTy && "Must have set the convertedtoty by this point!");
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// The number of bits required is the maximum of the upper and
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// lower limits, plus one so it can be signed.
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unsigned MinBW = std::max(R.getLower().getMinSignedBits(),
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R.getUpper().getMinSignedBits()) + 1;
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DEBUG(dbgs() << "F2I: MinBitwidth=" << MinBW << ", R: " << R << "\n");
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// If we've run off the realms of the exactly representable integers,
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// the floating point result will differ from an integer approximation.
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// Do we need more bits than are in the mantissa of the type we converted
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// to? semanticsPrecision returns the number of mantissa bits plus one
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// for the sign bit.
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unsigned MaxRepresentableBits
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= APFloat::semanticsPrecision(ConvertedToTy->getFltSemantics()) - 1;
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if (MinBW > MaxRepresentableBits) {
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DEBUG(dbgs() << "F2I: Value not guaranteed to be representable!\n");
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continue;
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}
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if (MinBW > 64) {
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DEBUG(dbgs() << "F2I: Value requires more than 64 bits to represent!\n");
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continue;
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}
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// OK, R is known to be representable. Now pick a type for it.
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// FIXME: Pick the smallest legal type that will fit.
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Type *Ty = (MinBW > 32) ? Type::getInt64Ty(*Ctx) : Type::getInt32Ty(*Ctx);
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for (auto MI = ECs.member_begin(It), ME = ECs.member_end();
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MI != ME; ++MI)
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convert(*MI, Ty);
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MadeChange = true;
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}
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return MadeChange;
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}
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Value *Float2IntPass::convert(Instruction *I, Type *ToTy) {
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if (ConvertedInsts.find(I) != ConvertedInsts.end())
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// Already converted this instruction.
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return ConvertedInsts[I];
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SmallVector<Value*,4> NewOperands;
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for (Value *V : I->operands()) {
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// Don't recurse if we're an instruction that terminates the path.
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if (I->getOpcode() == Instruction::UIToFP ||
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I->getOpcode() == Instruction::SIToFP) {
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NewOperands.push_back(V);
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} else if (Instruction *VI = dyn_cast<Instruction>(V)) {
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NewOperands.push_back(convert(VI, ToTy));
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} else if (ConstantFP *CF = dyn_cast<ConstantFP>(V)) {
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APSInt Val(ToTy->getPrimitiveSizeInBits(), /*IsUnsigned=*/false);
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bool Exact;
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CF->getValueAPF().convertToInteger(Val,
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APFloat::rmNearestTiesToEven,
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&Exact);
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NewOperands.push_back(ConstantInt::get(ToTy, Val));
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} else {
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llvm_unreachable("Unhandled operand type?");
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}
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}
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// Now create a new instruction.
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IRBuilder<> IRB(I);
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Value *NewV = nullptr;
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switch (I->getOpcode()) {
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default: llvm_unreachable("Unhandled instruction!");
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case Instruction::FPToUI:
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NewV = IRB.CreateZExtOrTrunc(NewOperands[0], I->getType());
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break;
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case Instruction::FPToSI:
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NewV = IRB.CreateSExtOrTrunc(NewOperands[0], I->getType());
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break;
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case Instruction::FCmp: {
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CmpInst::Predicate P = mapFCmpPred(cast<CmpInst>(I)->getPredicate());
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assert(P != CmpInst::BAD_ICMP_PREDICATE && "Unhandled predicate!");
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NewV = IRB.CreateICmp(P, NewOperands[0], NewOperands[1], I->getName());
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break;
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}
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case Instruction::UIToFP:
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NewV = IRB.CreateZExtOrTrunc(NewOperands[0], ToTy);
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break;
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case Instruction::SIToFP:
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NewV = IRB.CreateSExtOrTrunc(NewOperands[0], ToTy);
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break;
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case Instruction::FAdd:
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case Instruction::FSub:
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case Instruction::FMul:
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NewV = IRB.CreateBinOp(mapBinOpcode(I->getOpcode()),
|
|
NewOperands[0], NewOperands[1],
|
|
I->getName());
|
|
break;
|
|
}
|
|
|
|
// If we're a root instruction, RAUW.
|
|
if (Roots.count(I))
|
|
I->replaceAllUsesWith(NewV);
|
|
|
|
ConvertedInsts[I] = NewV;
|
|
return NewV;
|
|
}
|
|
|
|
// Perform dead code elimination on the instructions we just modified.
|
|
void Float2IntPass::cleanup() {
|
|
for (auto &I : reverse(ConvertedInsts))
|
|
I.first->eraseFromParent();
|
|
}
|
|
|
|
bool Float2IntPass::runImpl(Function &F) {
|
|
DEBUG(dbgs() << "F2I: Looking at function " << F.getName() << "\n");
|
|
// Clear out all state.
|
|
ECs = EquivalenceClasses<Instruction*>();
|
|
SeenInsts.clear();
|
|
ConvertedInsts.clear();
|
|
Roots.clear();
|
|
|
|
Ctx = &F.getParent()->getContext();
|
|
|
|
findRoots(F, Roots);
|
|
|
|
walkBackwards(Roots);
|
|
walkForwards();
|
|
|
|
bool Modified = validateAndTransform();
|
|
if (Modified)
|
|
cleanup();
|
|
return Modified;
|
|
}
|
|
|
|
namespace llvm {
|
|
FunctionPass *createFloat2IntPass() { return new Float2IntLegacyPass(); }
|
|
|
|
PreservedAnalyses Float2IntPass::run(Function &F, FunctionAnalysisManager &) {
|
|
if (!runImpl(F))
|
|
return PreservedAnalyses::all();
|
|
else {
|
|
// FIXME: This should also 'preserve the CFG'.
|
|
PreservedAnalyses PA;
|
|
PA.preserve<GlobalsAA>();
|
|
return PA;
|
|
}
|
|
}
|
|
} // End namespace llvm
|