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-rw-r--r--llvm/lib/Target/X86/X86WinAllocaExpander.cpp294
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diff --git a/llvm/lib/Target/X86/X86WinAllocaExpander.cpp b/llvm/lib/Target/X86/X86WinAllocaExpander.cpp
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--- a/llvm/lib/Target/X86/X86WinAllocaExpander.cpp
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-//===----- X86WinAllocaExpander.cpp - Expand WinAlloca pseudo instruction -===//
-//
-// The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-//
-// This file defines a pass that expands WinAlloca pseudo-instructions.
-//
-// It performs a conservative analysis to determine whether each allocation
-// falls within a region of the stack that is safe to use, or whether stack
-// probes must be emitted.
-//
-//===----------------------------------------------------------------------===//
-
-#include "X86.h"
-#include "X86InstrBuilder.h"
-#include "X86InstrInfo.h"
-#include "X86MachineFunctionInfo.h"
-#include "X86Subtarget.h"
-#include "llvm/ADT/PostOrderIterator.h"
-#include "llvm/CodeGen/MachineFunctionPass.h"
-#include "llvm/CodeGen/MachineInstrBuilder.h"
-#include "llvm/CodeGen/MachineRegisterInfo.h"
-#include "llvm/CodeGen/Passes.h"
-#include "llvm/IR/Function.h"
-#include "llvm/Support/raw_ostream.h"
-#include "llvm/Target/TargetInstrInfo.h"
-
-using namespace llvm;
-
-namespace {
-
-class X86WinAllocaExpander : public MachineFunctionPass {
-public:
- X86WinAllocaExpander() : MachineFunctionPass(ID) {}
-
- bool runOnMachineFunction(MachineFunction &MF) override;
-
-private:
- /// Strategies for lowering a WinAlloca.
- enum Lowering { TouchAndSub, Sub, Probe };
-
- /// Deterministic-order map from WinAlloca instruction to desired lowering.
- typedef MapVector<MachineInstr*, Lowering> LoweringMap;
-
- /// Compute which lowering to use for each WinAlloca instruction.
- void computeLowerings(MachineFunction &MF, LoweringMap& Lowerings);
-
- /// Get the appropriate lowering based on current offset and amount.
- Lowering getLowering(int64_t CurrentOffset, int64_t AllocaAmount);
-
- /// Lower a WinAlloca instruction.
- void lower(MachineInstr* MI, Lowering L);
-
- MachineRegisterInfo *MRI;
- const X86Subtarget *STI;
- const TargetInstrInfo *TII;
- const X86RegisterInfo *TRI;
- unsigned StackPtr;
- unsigned SlotSize;
- int64_t StackProbeSize;
-
- const char *getPassName() const override { return "X86 WinAlloca Expander"; }
- static char ID;
-};
-
-char X86WinAllocaExpander::ID = 0;
-
-} // end anonymous namespace
-
-FunctionPass *llvm::createX86WinAllocaExpander() {
- return new X86WinAllocaExpander();
-}
-
-/// Return the allocation amount for a WinAlloca instruction, or -1 if unknown.
-static int64_t getWinAllocaAmount(MachineInstr *MI, MachineRegisterInfo *MRI) {
- assert(MI->getOpcode() == X86::WIN_ALLOCA_32 ||
- MI->getOpcode() == X86::WIN_ALLOCA_64);
- assert(MI->getOperand(0).isReg());
-
- unsigned AmountReg = MI->getOperand(0).getReg();
- MachineInstr *Def = MRI->getUniqueVRegDef(AmountReg);
-
- // Look through copies.
- while (Def && Def->isCopy() && Def->getOperand(1).isReg())
- Def = MRI->getUniqueVRegDef(Def->getOperand(1).getReg());
-
- if (!Def ||
- (Def->getOpcode() != X86::MOV32ri && Def->getOpcode() != X86::MOV64ri) ||
- !Def->getOperand(1).isImm())
- return -1;
-
- return Def->getOperand(1).getImm();
-}
-
-X86WinAllocaExpander::Lowering
-X86WinAllocaExpander::getLowering(int64_t CurrentOffset,
- int64_t AllocaAmount) {
- // For a non-constant amount or a large amount, we have to probe.
- if (AllocaAmount < 0 || AllocaAmount > StackProbeSize)
- return Probe;
-
- // If it fits within the safe region of the stack, just subtract.
- if (CurrentOffset + AllocaAmount <= StackProbeSize)
- return Sub;
-
- // Otherwise, touch the current tip of the stack, then subtract.
- return TouchAndSub;
-}
-
-static bool isPushPop(const MachineInstr &MI) {
- switch (MI.getOpcode()) {
- case X86::PUSH32i8:
- case X86::PUSH32r:
- case X86::PUSH32rmm:
- case X86::PUSH32rmr:
- case X86::PUSHi32:
- case X86::PUSH64i8:
- case X86::PUSH64r:
- case X86::PUSH64rmm:
- case X86::PUSH64rmr:
- case X86::PUSH64i32:
- case X86::POP32r:
- case X86::POP64r:
- return true;
- default:
- return false;
- }
-}
-
-void X86WinAllocaExpander::computeLowerings(MachineFunction &MF,
- LoweringMap &Lowerings) {
- // Do a one-pass reverse post-order walk of the CFG to conservatively estimate
- // the offset between the stack pointer and the lowest touched part of the
- // stack, and use that to decide how to lower each WinAlloca instruction.
-
- // Initialize OutOffset[B], the stack offset at exit from B, to something big.
- DenseMap<MachineBasicBlock *, int64_t> OutOffset;
- for (MachineBasicBlock &MBB : MF)
- OutOffset[&MBB] = INT32_MAX;
-
- // Note: we don't know the offset at the start of the entry block since the
- // prologue hasn't been inserted yet, and how much that will adjust the stack
- // pointer depends on register spills, which have not been computed yet.
-
- // Compute the reverse post-order.
- ReversePostOrderTraversal<MachineFunction*> RPO(&MF);
-
- for (MachineBasicBlock *MBB : RPO) {
- int64_t Offset = -1;
- for (MachineBasicBlock *Pred : MBB->predecessors())
- Offset = std::max(Offset, OutOffset[Pred]);
- if (Offset == -1) Offset = INT32_MAX;
-
- for (MachineInstr &MI : *MBB) {
- if (MI.getOpcode() == X86::WIN_ALLOCA_32 ||
- MI.getOpcode() == X86::WIN_ALLOCA_64) {
- // A WinAlloca moves StackPtr, and potentially touches it.
- int64_t Amount = getWinAllocaAmount(&MI, MRI);
- Lowering L = getLowering(Offset, Amount);
- Lowerings[&MI] = L;
- switch (L) {
- case Sub:
- Offset += Amount;
- break;
- case TouchAndSub:
- Offset = Amount;
- break;
- case Probe:
- Offset = 0;
- break;
- }
- } else if (MI.isCall() || isPushPop(MI)) {
- // Calls, pushes and pops touch the tip of the stack.
- Offset = 0;
- } else if (MI.getOpcode() == X86::ADJCALLSTACKUP32 ||
- MI.getOpcode() == X86::ADJCALLSTACKUP64) {
- Offset -= MI.getOperand(0).getImm();
- } else if (MI.getOpcode() == X86::ADJCALLSTACKDOWN32 ||
- MI.getOpcode() == X86::ADJCALLSTACKDOWN64) {
- Offset += MI.getOperand(0).getImm();
- } else if (MI.modifiesRegister(StackPtr, TRI)) {
- // Any other modification of SP means we've lost track of it.
- Offset = INT32_MAX;
- }
- }
-
- OutOffset[MBB] = Offset;
- }
-}
-
-static unsigned getSubOpcode(bool Is64Bit, int64_t Amount) {
- if (Is64Bit)
- return isInt<8>(Amount) ? X86::SUB64ri8 : X86::SUB64ri32;
- return isInt<8>(Amount) ? X86::SUB32ri8 : X86::SUB32ri;
-}
-
-void X86WinAllocaExpander::lower(MachineInstr* MI, Lowering L) {
- DebugLoc DL = MI->getDebugLoc();
- MachineBasicBlock *MBB = MI->getParent();
- MachineBasicBlock::iterator I = *MI;
-
- int64_t Amount = getWinAllocaAmount(MI, MRI);
- if (Amount == 0) {
- MI->eraseFromParent();
- return;
- }
-
- bool Is64Bit = STI->is64Bit();
- assert(SlotSize == 4 || SlotSize == 8);
- unsigned RegA = (SlotSize == 8) ? X86::RAX : X86::EAX;
-
- switch (L) {
- case TouchAndSub:
- assert(Amount >= SlotSize);
-
- // Use a push to touch the top of the stack.
- BuildMI(*MBB, I, DL, TII->get(Is64Bit ? X86::PUSH64r : X86::PUSH32r))
- .addReg(RegA, RegState::Undef);
- Amount -= SlotSize;
- if (!Amount)
- break;
-
- // Fall through to make any remaining adjustment.
- case Sub:
- assert(Amount > 0);
- if (Amount == SlotSize) {
- // Use push to save size.
- BuildMI(*MBB, I, DL, TII->get(Is64Bit ? X86::PUSH64r : X86::PUSH32r))
- .addReg(RegA, RegState::Undef);
- } else {
- // Sub.
- BuildMI(*MBB, I, DL, TII->get(getSubOpcode(Is64Bit, Amount)), StackPtr)
- .addReg(StackPtr)
- .addImm(Amount);
- }
- break;
- case Probe:
- // The probe lowering expects the amount in RAX/EAX.
- BuildMI(*MBB, MI, DL, TII->get(TargetOpcode::COPY), RegA)
- .addReg(MI->getOperand(0).getReg());
-
- // Do the probe.
- STI->getFrameLowering()->emitStackProbe(*MBB->getParent(), *MBB, MI, DL,
- /*InPrologue=*/false);
- break;
- }
-
- unsigned AmountReg = MI->getOperand(0).getReg();
- MI->eraseFromParent();
-
- // Delete the definition of AmountReg, possibly walking a chain of copies.
- for (;;) {
- if (!MRI->use_empty(AmountReg))
- break;
- MachineInstr *AmountDef = MRI->getUniqueVRegDef(AmountReg);
- if (!AmountDef)
- break;
- if (AmountDef->isCopy() && AmountDef->getOperand(1).isReg())
- AmountReg = AmountDef->getOperand(1).isReg();
- AmountDef->eraseFromParent();
- break;
- }
-}
-
-bool X86WinAllocaExpander::runOnMachineFunction(MachineFunction &MF) {
- if (!MF.getInfo<X86MachineFunctionInfo>()->hasWinAlloca())
- return false;
-
- MRI = &MF.getRegInfo();
- STI = &MF.getSubtarget<X86Subtarget>();
- TII = STI->getInstrInfo();
- TRI = STI->getRegisterInfo();
- StackPtr = TRI->getStackRegister();
- SlotSize = TRI->getSlotSize();
-
- StackProbeSize = 4096;
- if (MF.getFunction()->hasFnAttribute("stack-probe-size")) {
- MF.getFunction()
- ->getFnAttribute("stack-probe-size")
- .getValueAsString()
- .getAsInteger(0, StackProbeSize);
- }
-
- LoweringMap Lowerings;
- computeLowerings(MF, Lowerings);
- for (auto &P : Lowerings)
- lower(P.first, P.second);
-
- return true;
-}
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