356 lines
14 KiB
C++
356 lines
14 KiB
C++
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//===- LocalStackSlotAllocation.cpp - Pre-allocate locals to stack slots --===//
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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 pass assigns local frame indices to stack slots relative to one another
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// and allocates additional base registers to access them when the target
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// estimates they are likely to be out of range of stack pointer and frame
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// pointer relative addressing.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "localstackalloc"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Instructions.h"
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#include "llvm/Intrinsics.h"
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#include "llvm/LLVMContext.h"
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#include "llvm/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/ADT/SmallSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/CodeGen/MachineFrameInfo.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetRegisterInfo.h"
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#include "llvm/Target/TargetFrameLowering.h"
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using namespace llvm;
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STATISTIC(NumAllocations, "Number of frame indices allocated into local block");
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STATISTIC(NumBaseRegisters, "Number of virtual frame base registers allocated");
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STATISTIC(NumReplacements, "Number of frame indices references replaced");
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namespace {
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class FrameRef {
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MachineBasicBlock::iterator MI; // Instr referencing the frame
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int64_t LocalOffset; // Local offset of the frame idx referenced
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public:
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FrameRef(MachineBasicBlock::iterator I, int64_t Offset) :
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MI(I), LocalOffset(Offset) {}
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bool operator<(const FrameRef &RHS) const {
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return LocalOffset < RHS.LocalOffset;
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}
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MachineBasicBlock::iterator getMachineInstr() { return MI; }
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};
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class LocalStackSlotPass: public MachineFunctionPass {
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SmallVector<int64_t,16> LocalOffsets;
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void AdjustStackOffset(MachineFrameInfo *MFI, int FrameIdx, int64_t &Offset,
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bool StackGrowsDown, unsigned &MaxAlign);
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void calculateFrameObjectOffsets(MachineFunction &Fn);
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bool insertFrameReferenceRegisters(MachineFunction &Fn);
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public:
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static char ID; // Pass identification, replacement for typeid
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explicit LocalStackSlotPass() : MachineFunctionPass(ID) { }
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bool runOnMachineFunction(MachineFunction &MF);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesCFG();
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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private:
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};
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} // end anonymous namespace
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char LocalStackSlotPass::ID = 0;
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char &llvm::LocalStackSlotAllocationID = LocalStackSlotPass::ID;
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INITIALIZE_PASS(LocalStackSlotPass, "localstackalloc",
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"Local Stack Slot Allocation", false, false)
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bool LocalStackSlotPass::runOnMachineFunction(MachineFunction &MF) {
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MachineFrameInfo *MFI = MF.getFrameInfo();
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const TargetRegisterInfo *TRI = MF.getTarget().getRegisterInfo();
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unsigned LocalObjectCount = MFI->getObjectIndexEnd();
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// If the target doesn't want/need this pass, or if there are no locals
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// to consider, early exit.
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if (!TRI->requiresVirtualBaseRegisters(MF) || LocalObjectCount == 0)
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return true;
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// Make sure we have enough space to store the local offsets.
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LocalOffsets.resize(MFI->getObjectIndexEnd());
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// Lay out the local blob.
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calculateFrameObjectOffsets(MF);
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// Insert virtual base registers to resolve frame index references.
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bool UsedBaseRegs = insertFrameReferenceRegisters(MF);
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// Tell MFI whether any base registers were allocated. PEI will only
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// want to use the local block allocations from this pass if there were any.
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// Otherwise, PEI can do a bit better job of getting the alignment right
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// without a hole at the start since it knows the alignment of the stack
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// at the start of local allocation, and this pass doesn't.
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MFI->setUseLocalStackAllocationBlock(UsedBaseRegs);
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return true;
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}
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/// AdjustStackOffset - Helper function used to adjust the stack frame offset.
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void LocalStackSlotPass::AdjustStackOffset(MachineFrameInfo *MFI,
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int FrameIdx, int64_t &Offset,
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bool StackGrowsDown,
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unsigned &MaxAlign) {
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// If the stack grows down, add the object size to find the lowest address.
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if (StackGrowsDown)
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Offset += MFI->getObjectSize(FrameIdx);
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unsigned Align = MFI->getObjectAlignment(FrameIdx);
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// If the alignment of this object is greater than that of the stack, then
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// increase the stack alignment to match.
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MaxAlign = std::max(MaxAlign, Align);
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// Adjust to alignment boundary.
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Offset = (Offset + Align - 1) / Align * Align;
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int64_t LocalOffset = StackGrowsDown ? -Offset : Offset;
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DEBUG(dbgs() << "Allocate FI(" << FrameIdx << ") to local offset "
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<< LocalOffset << "\n");
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// Keep the offset available for base register allocation
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LocalOffsets[FrameIdx] = LocalOffset;
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// And tell MFI about it for PEI to use later
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MFI->mapLocalFrameObject(FrameIdx, LocalOffset);
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if (!StackGrowsDown)
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Offset += MFI->getObjectSize(FrameIdx);
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++NumAllocations;
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}
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/// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
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/// abstract stack objects.
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///
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void LocalStackSlotPass::calculateFrameObjectOffsets(MachineFunction &Fn) {
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// Loop over all of the stack objects, assigning sequential addresses...
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MachineFrameInfo *MFI = Fn.getFrameInfo();
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const TargetFrameLowering &TFI = *Fn.getTarget().getFrameLowering();
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bool StackGrowsDown =
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TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
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int64_t Offset = 0;
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unsigned MaxAlign = 0;
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// Make sure that the stack protector comes before the local variables on the
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// stack.
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SmallSet<int, 16> LargeStackObjs;
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if (MFI->getStackProtectorIndex() >= 0) {
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AdjustStackOffset(MFI, MFI->getStackProtectorIndex(), Offset,
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StackGrowsDown, MaxAlign);
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// Assign large stack objects first.
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for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
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if (MFI->isDeadObjectIndex(i))
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continue;
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if (MFI->getStackProtectorIndex() == (int)i)
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continue;
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if (!MFI->MayNeedStackProtector(i))
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continue;
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AdjustStackOffset(MFI, i, Offset, StackGrowsDown, MaxAlign);
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LargeStackObjs.insert(i);
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}
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}
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// Then assign frame offsets to stack objects that are not used to spill
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// callee saved registers.
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for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
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if (MFI->isDeadObjectIndex(i))
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continue;
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if (MFI->getStackProtectorIndex() == (int)i)
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continue;
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if (LargeStackObjs.count(i))
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continue;
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AdjustStackOffset(MFI, i, Offset, StackGrowsDown, MaxAlign);
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}
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// Remember how big this blob of stack space is
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MFI->setLocalFrameSize(Offset);
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MFI->setLocalFrameMaxAlign(MaxAlign);
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}
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static inline bool
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lookupCandidateBaseReg(const SmallVector<std::pair<unsigned, int64_t>, 8> &Regs,
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std::pair<unsigned, int64_t> &RegOffset,
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int64_t FrameSizeAdjust,
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int64_t LocalFrameOffset,
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const MachineInstr *MI,
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const TargetRegisterInfo *TRI) {
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unsigned e = Regs.size();
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for (unsigned i = 0; i < e; ++i) {
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RegOffset = Regs[i];
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// Check if the relative offset from the where the base register references
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// to the target address is in range for the instruction.
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int64_t Offset = FrameSizeAdjust + LocalFrameOffset - RegOffset.second;
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if (TRI->isFrameOffsetLegal(MI, Offset))
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return true;
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}
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return false;
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}
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bool LocalStackSlotPass::insertFrameReferenceRegisters(MachineFunction &Fn) {
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// Scan the function's instructions looking for frame index references.
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// For each, ask the target if it wants a virtual base register for it
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// based on what we can tell it about where the local will end up in the
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// stack frame. If it wants one, re-use a suitable one we've previously
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// allocated, or if there isn't one that fits the bill, allocate a new one
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// and ask the target to create a defining instruction for it.
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bool UsedBaseReg = false;
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MachineFrameInfo *MFI = Fn.getFrameInfo();
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const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
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const TargetFrameLowering &TFI = *Fn.getTarget().getFrameLowering();
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bool StackGrowsDown =
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TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
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// Collect all of the instructions in the block that reference
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// a frame index. Also store the frame index referenced to ease later
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// lookup. (For any insn that has more than one FI reference, we arbitrarily
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// choose the first one).
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SmallVector<FrameRef, 64> FrameReferenceInsns;
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// A base register definition is a register + offset pair.
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SmallVector<std::pair<unsigned, int64_t>, 8> BaseRegisters;
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for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
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for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
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MachineInstr *MI = I;
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// Debug value instructions can't be out of range, so they don't need
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// any updates.
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if (MI->isDebugValue())
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continue;
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// For now, allocate the base register(s) within the basic block
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// where they're used, and don't try to keep them around outside
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// of that. It may be beneficial to try sharing them more broadly
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// than that, but the increased register pressure makes that a
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// tricky thing to balance. Investigate if re-materializing these
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// becomes an issue.
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for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
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// Consider replacing all frame index operands that reference
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// an object allocated in the local block.
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if (MI->getOperand(i).isFI()) {
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// Don't try this with values not in the local block.
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if (!MFI->isObjectPreAllocated(MI->getOperand(i).getIndex()))
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break;
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FrameReferenceInsns.
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push_back(FrameRef(MI, LocalOffsets[MI->getOperand(i).getIndex()]));
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break;
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}
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}
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}
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}
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// Sort the frame references by local offset
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array_pod_sort(FrameReferenceInsns.begin(), FrameReferenceInsns.end());
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MachineBasicBlock *Entry = Fn.begin();
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// Loop through the frame references and allocate for them as necessary.
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for (int ref = 0, e = FrameReferenceInsns.size(); ref < e ; ++ref) {
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MachineBasicBlock::iterator I =
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FrameReferenceInsns[ref].getMachineInstr();
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MachineInstr *MI = I;
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for (unsigned idx = 0, e = MI->getNumOperands(); idx != e; ++idx) {
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// Consider replacing all frame index operands that reference
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// an object allocated in the local block.
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if (MI->getOperand(idx).isFI()) {
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int FrameIdx = MI->getOperand(idx).getIndex();
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assert(MFI->isObjectPreAllocated(FrameIdx) &&
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"Only pre-allocated locals expected!");
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DEBUG(dbgs() << "Considering: " << *MI);
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if (TRI->needsFrameBaseReg(MI, LocalOffsets[FrameIdx])) {
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unsigned BaseReg = 0;
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int64_t Offset = 0;
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int64_t FrameSizeAdjust =
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StackGrowsDown ? MFI->getLocalFrameSize() : 0;
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DEBUG(dbgs() << " Replacing FI in: " << *MI);
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// If we have a suitable base register available, use it; otherwise
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// create a new one. Note that any offset encoded in the
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// instruction itself will be taken into account by the target,
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// so we don't have to adjust for it here when reusing a base
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// register.
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std::pair<unsigned, int64_t> RegOffset;
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if (lookupCandidateBaseReg(BaseRegisters, RegOffset,
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FrameSizeAdjust,
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LocalOffsets[FrameIdx],
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MI, TRI)) {
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DEBUG(dbgs() << " Reusing base register " <<
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RegOffset.first << "\n");
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// We found a register to reuse.
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BaseReg = RegOffset.first;
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Offset = FrameSizeAdjust + LocalOffsets[FrameIdx] -
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RegOffset.second;
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} else {
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// No previously defined register was in range, so create a
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// new one.
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int64_t InstrOffset = TRI->getFrameIndexInstrOffset(MI, idx);
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const TargetRegisterClass *RC = TRI->getPointerRegClass();
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BaseReg = Fn.getRegInfo().createVirtualRegister(RC);
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DEBUG(dbgs() << " Materializing base register " << BaseReg <<
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" at frame local offset " <<
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LocalOffsets[FrameIdx] + InstrOffset << "\n");
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// Tell the target to insert the instruction to initialize
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// the base register.
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// MachineBasicBlock::iterator InsertionPt = Entry->begin();
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TRI->materializeFrameBaseRegister(Entry, BaseReg, FrameIdx,
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InstrOffset);
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// The base register already includes any offset specified
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// by the instruction, so account for that so it doesn't get
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// applied twice.
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Offset = -InstrOffset;
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int64_t BaseOffset = FrameSizeAdjust + LocalOffsets[FrameIdx] +
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InstrOffset;
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BaseRegisters.push_back(
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std::pair<unsigned, int64_t>(BaseReg, BaseOffset));
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++NumBaseRegisters;
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UsedBaseReg = true;
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}
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assert(BaseReg != 0 && "Unable to allocate virtual base register!");
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// Modify the instruction to use the new base register rather
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// than the frame index operand.
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TRI->resolveFrameIndex(I, BaseReg, Offset);
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DEBUG(dbgs() << "Resolved: " << *MI);
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++NumReplacements;
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}
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}
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}
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}
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return UsedBaseReg;
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}
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