mirror of
https://github.com/c64scene-ar/llvm-6502.git
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feae667742
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217350 91177308-0d34-0410-b5e6-96231b3b80d8
423 lines
16 KiB
C++
423 lines
16 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/AssumptionTracker.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<AssumptionTracker>();
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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<LoopInfo>();
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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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AssumptionTracker *AT;
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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(AssumptionTracker)
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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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// 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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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 && NewIncAlignment) {
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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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AT = &getAnalysis<AssumptionTracker>();
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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 &I : AT->assumptions(&F))
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Changed |= processAssumption(I);
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return Changed;
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}
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