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https://github.com/c64scene-ar/llvm-6502.git
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de5df29556
a LoopInfoWrapperPass to wire the object up to the legacy pass manager. This switches all the clients of LoopInfo over and paves the way to port LoopInfo to the new pass manager. No functionality change is intended with this iteration. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226373 91177308-0d34-0410-b5e6-96231b3b80d8
429 lines
17 KiB
C++
429 lines
17 KiB
C++
//===----------------------- AlignmentFromAssumptions.cpp -----------------===//
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// Set Load/Store Alignments From Assumptions
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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 a ScalarEvolution-based transformation to set
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// the alignments of load, stores and memory intrinsics based on the truth
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// expressions of assume intrinsics. The primary motivation is to handle
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// complex alignment assumptions that apply to vector loads and stores that
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// appear after vectorization and unrolling.
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//
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//===----------------------------------------------------------------------===//
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#define AA_NAME "alignment-from-assumptions"
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#define DEBUG_TYPE AA_NAME
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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/Analysis/AssumptionCache.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.h"
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#include "llvm/IR/Constant.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Intrinsics.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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STATISTIC(NumLoadAlignChanged,
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"Number of loads changed by alignment assumptions");
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STATISTIC(NumStoreAlignChanged,
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"Number of stores changed by alignment assumptions");
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STATISTIC(NumMemIntAlignChanged,
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"Number of memory intrinsics changed by alignment assumptions");
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namespace {
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struct AlignmentFromAssumptions : public FunctionPass {
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static char ID; // Pass identification, replacement for typeid
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AlignmentFromAssumptions() : FunctionPass(ID) {
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initializeAlignmentFromAssumptionsPass(*PassRegistry::getPassRegistry());
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}
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bool runOnFunction(Function &F);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<AssumptionCacheTracker>();
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AU.addRequired<ScalarEvolution>();
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AU.addRequired<DominatorTreeWrapperPass>();
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AU.setPreservesCFG();
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AU.addPreserved<LoopInfoWrapperPass>();
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AU.addPreserved<DominatorTreeWrapperPass>();
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AU.addPreserved<ScalarEvolution>();
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}
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// For memory transfers, we need a common alignment for both the source and
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// destination. If we have a new alignment for only one operand of a transfer
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// instruction, save it in these maps. If we reach the other operand through
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// another assumption later, then we may change the alignment at that point.
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DenseMap<MemTransferInst *, unsigned> NewDestAlignments, NewSrcAlignments;
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ScalarEvolution *SE;
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DominatorTree *DT;
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const DataLayout *DL;
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bool extractAlignmentInfo(CallInst *I, Value *&AAPtr, const SCEV *&AlignSCEV,
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const SCEV *&OffSCEV);
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bool processAssumption(CallInst *I);
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};
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}
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char AlignmentFromAssumptions::ID = 0;
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static const char aip_name[] = "Alignment from assumptions";
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INITIALIZE_PASS_BEGIN(AlignmentFromAssumptions, AA_NAME,
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aip_name, false, false)
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INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
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INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
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INITIALIZE_PASS_END(AlignmentFromAssumptions, AA_NAME,
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aip_name, false, false)
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FunctionPass *llvm::createAlignmentFromAssumptionsPass() {
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return new AlignmentFromAssumptions();
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}
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// Given an expression for the (constant) alignment, AlignSCEV, and an
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// expression for the displacement between a pointer and the aligned address,
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// DiffSCEV, compute the alignment of the displaced pointer if it can be reduced
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// to a constant. Using SCEV to compute alignment handles the case where
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// DiffSCEV is a recurrence with constant start such that the aligned offset
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// is constant. e.g. {16,+,32} % 32 -> 16.
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static unsigned getNewAlignmentDiff(const SCEV *DiffSCEV,
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const SCEV *AlignSCEV,
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ScalarEvolution *SE) {
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// DiffUnits = Diff % int64_t(Alignment)
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const SCEV *DiffAlignDiv = SE->getUDivExpr(DiffSCEV, AlignSCEV);
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const SCEV *DiffAlign = SE->getMulExpr(DiffAlignDiv, AlignSCEV);
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const SCEV *DiffUnitsSCEV = SE->getMinusSCEV(DiffAlign, DiffSCEV);
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DEBUG(dbgs() << "\talignment relative to " << *AlignSCEV << " is " <<
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*DiffUnitsSCEV << " (diff: " << *DiffSCEV << ")\n");
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if (const SCEVConstant *ConstDUSCEV =
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dyn_cast<SCEVConstant>(DiffUnitsSCEV)) {
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int64_t DiffUnits = ConstDUSCEV->getValue()->getSExtValue();
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// If the displacement is an exact multiple of the alignment, then the
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// displaced pointer has the same alignment as the aligned pointer, so
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// return the alignment value.
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if (!DiffUnits)
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return (unsigned)
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cast<SCEVConstant>(AlignSCEV)->getValue()->getSExtValue();
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// If the displacement is not an exact multiple, but the remainder is a
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// constant, then return this remainder (but only if it is a power of 2).
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uint64_t DiffUnitsAbs = abs64(DiffUnits);
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if (isPowerOf2_64(DiffUnitsAbs))
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return (unsigned) DiffUnitsAbs;
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}
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return 0;
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}
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// There is an address given by an offset OffSCEV from AASCEV which has an
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// alignment AlignSCEV. Use that information, if possible, to compute a new
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// alignment for Ptr.
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static unsigned getNewAlignment(const SCEV *AASCEV, const SCEV *AlignSCEV,
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const SCEV *OffSCEV, Value *Ptr,
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ScalarEvolution *SE) {
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const SCEV *PtrSCEV = SE->getSCEV(Ptr);
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const SCEV *DiffSCEV = SE->getMinusSCEV(PtrSCEV, AASCEV);
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// On 32-bit platforms, DiffSCEV might now have type i32 -- we've always
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// sign-extended OffSCEV to i64, so make sure they agree again.
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DiffSCEV = SE->getNoopOrSignExtend(DiffSCEV, OffSCEV->getType());
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// What we really want to know is the overall offset to the aligned
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// address. This address is displaced by the provided offset.
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DiffSCEV = SE->getMinusSCEV(DiffSCEV, OffSCEV);
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DEBUG(dbgs() << "AFI: alignment of " << *Ptr << " relative to " <<
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*AlignSCEV << " and offset " << *OffSCEV <<
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" using diff " << *DiffSCEV << "\n");
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unsigned NewAlignment = getNewAlignmentDiff(DiffSCEV, AlignSCEV, SE);
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DEBUG(dbgs() << "\tnew alignment: " << NewAlignment << "\n");
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if (NewAlignment) {
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return NewAlignment;
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} else if (const SCEVAddRecExpr *DiffARSCEV =
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dyn_cast<SCEVAddRecExpr>(DiffSCEV)) {
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// The relative offset to the alignment assumption did not yield a constant,
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// but we should try harder: if we assume that a is 32-byte aligned, then in
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// for (i = 0; i < 1024; i += 4) r += a[i]; not all of the loads from a are
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// 32-byte aligned, but instead alternate between 32 and 16-byte alignment.
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// As a result, the new alignment will not be a constant, but can still
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// be improved over the default (of 4) to 16.
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const SCEV *DiffStartSCEV = DiffARSCEV->getStart();
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const SCEV *DiffIncSCEV = DiffARSCEV->getStepRecurrence(*SE);
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DEBUG(dbgs() << "\ttrying start/inc alignment using start " <<
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*DiffStartSCEV << " and inc " << *DiffIncSCEV << "\n");
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// Now compute the new alignment using the displacement to the value in the
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// first iteration, and also the alignment using the per-iteration delta.
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// If these are the same, then use that answer. Otherwise, use the smaller
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// one, but only if it divides the larger one.
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NewAlignment = getNewAlignmentDiff(DiffStartSCEV, AlignSCEV, SE);
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unsigned NewIncAlignment = getNewAlignmentDiff(DiffIncSCEV, AlignSCEV, SE);
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DEBUG(dbgs() << "\tnew start alignment: " << NewAlignment << "\n");
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DEBUG(dbgs() << "\tnew inc alignment: " << NewIncAlignment << "\n");
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if (!NewAlignment || !NewIncAlignment) {
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return 0;
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} else if (NewAlignment > NewIncAlignment) {
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if (NewAlignment % NewIncAlignment == 0) {
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DEBUG(dbgs() << "\tnew start/inc alignment: " <<
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NewIncAlignment << "\n");
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return NewIncAlignment;
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}
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} else if (NewIncAlignment > NewAlignment) {
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if (NewIncAlignment % NewAlignment == 0) {
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DEBUG(dbgs() << "\tnew start/inc alignment: " <<
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NewAlignment << "\n");
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return NewAlignment;
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}
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} else if (NewIncAlignment == NewAlignment) {
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DEBUG(dbgs() << "\tnew start/inc alignment: " <<
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NewAlignment << "\n");
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return NewAlignment;
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}
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}
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return 0;
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}
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bool AlignmentFromAssumptions::extractAlignmentInfo(CallInst *I,
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Value *&AAPtr, const SCEV *&AlignSCEV,
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const SCEV *&OffSCEV) {
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// An alignment assume must be a statement about the least-significant
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// bits of the pointer being zero, possibly with some offset.
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ICmpInst *ICI = dyn_cast<ICmpInst>(I->getArgOperand(0));
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if (!ICI)
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return false;
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// This must be an expression of the form: x & m == 0.
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if (ICI->getPredicate() != ICmpInst::ICMP_EQ)
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return false;
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// Swap things around so that the RHS is 0.
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Value *CmpLHS = ICI->getOperand(0);
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Value *CmpRHS = ICI->getOperand(1);
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const SCEV *CmpLHSSCEV = SE->getSCEV(CmpLHS);
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const SCEV *CmpRHSSCEV = SE->getSCEV(CmpRHS);
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if (CmpLHSSCEV->isZero())
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std::swap(CmpLHS, CmpRHS);
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else if (!CmpRHSSCEV->isZero())
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return false;
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BinaryOperator *CmpBO = dyn_cast<BinaryOperator>(CmpLHS);
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if (!CmpBO || CmpBO->getOpcode() != Instruction::And)
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return false;
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// Swap things around so that the right operand of the and is a constant
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// (the mask); we cannot deal with variable masks.
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Value *AndLHS = CmpBO->getOperand(0);
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Value *AndRHS = CmpBO->getOperand(1);
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const SCEV *AndLHSSCEV = SE->getSCEV(AndLHS);
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const SCEV *AndRHSSCEV = SE->getSCEV(AndRHS);
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if (isa<SCEVConstant>(AndLHSSCEV)) {
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std::swap(AndLHS, AndRHS);
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std::swap(AndLHSSCEV, AndRHSSCEV);
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}
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const SCEVConstant *MaskSCEV = dyn_cast<SCEVConstant>(AndRHSSCEV);
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if (!MaskSCEV)
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return false;
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// The mask must have some trailing ones (otherwise the condition is
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// trivial and tells us nothing about the alignment of the left operand).
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unsigned TrailingOnes =
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MaskSCEV->getValue()->getValue().countTrailingOnes();
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if (!TrailingOnes)
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return false;
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// Cap the alignment at the maximum with which LLVM can deal (and make sure
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// we don't overflow the shift).
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uint64_t Alignment;
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TrailingOnes = std::min(TrailingOnes,
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unsigned(sizeof(unsigned) * CHAR_BIT - 1));
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Alignment = std::min(1u << TrailingOnes, +Value::MaximumAlignment);
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Type *Int64Ty = Type::getInt64Ty(I->getParent()->getParent()->getContext());
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AlignSCEV = SE->getConstant(Int64Ty, Alignment);
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// The LHS might be a ptrtoint instruction, or it might be the pointer
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// with an offset.
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AAPtr = nullptr;
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OffSCEV = nullptr;
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if (PtrToIntInst *PToI = dyn_cast<PtrToIntInst>(AndLHS)) {
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AAPtr = PToI->getPointerOperand();
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OffSCEV = SE->getConstant(Int64Ty, 0);
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} else if (const SCEVAddExpr* AndLHSAddSCEV =
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dyn_cast<SCEVAddExpr>(AndLHSSCEV)) {
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// Try to find the ptrtoint; subtract it and the rest is the offset.
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for (SCEVAddExpr::op_iterator J = AndLHSAddSCEV->op_begin(),
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JE = AndLHSAddSCEV->op_end(); J != JE; ++J)
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if (const SCEVUnknown *OpUnk = dyn_cast<SCEVUnknown>(*J))
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if (PtrToIntInst *PToI = dyn_cast<PtrToIntInst>(OpUnk->getValue())) {
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AAPtr = PToI->getPointerOperand();
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OffSCEV = SE->getMinusSCEV(AndLHSAddSCEV, *J);
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break;
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}
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}
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if (!AAPtr)
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return false;
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// Sign extend the offset to 64 bits (so that it is like all of the other
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// expressions).
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unsigned OffSCEVBits = OffSCEV->getType()->getPrimitiveSizeInBits();
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if (OffSCEVBits < 64)
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OffSCEV = SE->getSignExtendExpr(OffSCEV, Int64Ty);
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else if (OffSCEVBits > 64)
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return false;
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AAPtr = AAPtr->stripPointerCasts();
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return true;
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}
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bool AlignmentFromAssumptions::processAssumption(CallInst *ACall) {
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Value *AAPtr;
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const SCEV *AlignSCEV, *OffSCEV;
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if (!extractAlignmentInfo(ACall, AAPtr, AlignSCEV, OffSCEV))
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return false;
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const SCEV *AASCEV = SE->getSCEV(AAPtr);
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// Apply the assumption to all other users of the specified pointer.
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SmallPtrSet<Instruction *, 32> Visited;
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SmallVector<Instruction*, 16> WorkList;
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for (User *J : AAPtr->users()) {
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if (J == ACall)
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continue;
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if (Instruction *K = dyn_cast<Instruction>(J))
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if (isValidAssumeForContext(ACall, K, DL, DT))
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WorkList.push_back(K);
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}
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while (!WorkList.empty()) {
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Instruction *J = WorkList.pop_back_val();
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if (LoadInst *LI = dyn_cast<LoadInst>(J)) {
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unsigned NewAlignment = getNewAlignment(AASCEV, AlignSCEV, OffSCEV,
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LI->getPointerOperand(), SE);
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if (NewAlignment > LI->getAlignment()) {
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LI->setAlignment(NewAlignment);
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++NumLoadAlignChanged;
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}
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} else if (StoreInst *SI = dyn_cast<StoreInst>(J)) {
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unsigned NewAlignment = getNewAlignment(AASCEV, AlignSCEV, OffSCEV,
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SI->getPointerOperand(), SE);
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if (NewAlignment > SI->getAlignment()) {
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SI->setAlignment(NewAlignment);
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++NumStoreAlignChanged;
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}
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} else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(J)) {
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unsigned NewDestAlignment = getNewAlignment(AASCEV, AlignSCEV, OffSCEV,
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MI->getDest(), SE);
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// For memory transfers, we need a common alignment for both the
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// source and destination. If we have a new alignment for this
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// instruction, but only for one operand, save it. If we reach the
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// other operand through another assumption later, then we may
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// change the alignment at that point.
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if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) {
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unsigned NewSrcAlignment = getNewAlignment(AASCEV, AlignSCEV, OffSCEV,
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MTI->getSource(), SE);
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DenseMap<MemTransferInst *, unsigned>::iterator DI =
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NewDestAlignments.find(MTI);
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unsigned AltDestAlignment = (DI == NewDestAlignments.end()) ?
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0 : DI->second;
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DenseMap<MemTransferInst *, unsigned>::iterator SI =
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NewSrcAlignments.find(MTI);
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unsigned AltSrcAlignment = (SI == NewSrcAlignments.end()) ?
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0 : SI->second;
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DEBUG(dbgs() << "\tmem trans: " << NewDestAlignment << " " <<
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AltDestAlignment << " " << NewSrcAlignment <<
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" " << AltSrcAlignment << "\n");
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// Of these four alignments, pick the largest possible...
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unsigned NewAlignment = 0;
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if (NewDestAlignment <= std::max(NewSrcAlignment, AltSrcAlignment))
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NewAlignment = std::max(NewAlignment, NewDestAlignment);
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if (AltDestAlignment <= std::max(NewSrcAlignment, AltSrcAlignment))
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NewAlignment = std::max(NewAlignment, AltDestAlignment);
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if (NewSrcAlignment <= std::max(NewDestAlignment, AltDestAlignment))
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NewAlignment = std::max(NewAlignment, NewSrcAlignment);
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if (AltSrcAlignment <= std::max(NewDestAlignment, AltDestAlignment))
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NewAlignment = std::max(NewAlignment, AltSrcAlignment);
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if (NewAlignment > MI->getAlignment()) {
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MI->setAlignment(ConstantInt::get(Type::getInt32Ty(
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MI->getParent()->getContext()), NewAlignment));
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++NumMemIntAlignChanged;
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}
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NewDestAlignments.insert(std::make_pair(MTI, NewDestAlignment));
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NewSrcAlignments.insert(std::make_pair(MTI, NewSrcAlignment));
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} else if (NewDestAlignment > MI->getAlignment()) {
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assert((!isa<MemIntrinsic>(MI) || isa<MemSetInst>(MI)) &&
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"Unknown memory intrinsic");
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MI->setAlignment(ConstantInt::get(Type::getInt32Ty(
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MI->getParent()->getContext()), NewDestAlignment));
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++NumMemIntAlignChanged;
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}
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}
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// Now that we've updated that use of the pointer, look for other uses of
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// the pointer to update.
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Visited.insert(J);
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for (User *UJ : J->users()) {
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Instruction *K = cast<Instruction>(UJ);
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if (!Visited.count(K) && isValidAssumeForContext(ACall, K, DL, DT))
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WorkList.push_back(K);
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}
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}
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return true;
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}
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bool AlignmentFromAssumptions::runOnFunction(Function &F) {
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bool Changed = false;
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auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
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SE = &getAnalysis<ScalarEvolution>();
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DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
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DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
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DL = DLP ? &DLP->getDataLayout() : nullptr;
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NewDestAlignments.clear();
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NewSrcAlignments.clear();
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for (auto &AssumeVH : AC.assumptions())
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if (AssumeVH)
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Changed |= processAssumption(cast<CallInst>(AssumeVH));
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return Changed;
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}
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