llvm-project/llvm/lib/CodeGen/SwiftErrorValueTracking.cpp

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//===-- SwiftErrorValueTracking.cpp --------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This implements a limited mem2reg-like analysis to promote uses of function
// arguments and allocas marked with swiftalloc from memory into virtual
// registers tracked by this class.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/SwiftErrorValueTracking.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetLowering.h"
#include "llvm/IR/Value.h"
using namespace llvm;
Register SwiftErrorValueTracking::getOrCreateVReg(const MachineBasicBlock *MBB,
const Value *Val) {
auto Key = std::make_pair(MBB, Val);
auto It = VRegDefMap.find(Key);
// If this is the first use of this swifterror value in this basic block,
// create a new virtual register.
// After we processed all basic blocks we will satisfy this "upwards exposed
// use" by inserting a copy or phi at the beginning of this block.
if (It == VRegDefMap.end()) {
auto &DL = MF->getDataLayout();
const TargetRegisterClass *RC = TLI->getRegClassFor(TLI->getPointerTy(DL));
auto VReg = MF->getRegInfo().createVirtualRegister(RC);
VRegDefMap[Key] = VReg;
VRegUpwardsUse[Key] = VReg;
return VReg;
} else
return It->second;
}
void SwiftErrorValueTracking::setCurrentVReg(const MachineBasicBlock *MBB,
const Value *Val, Register VReg) {
VRegDefMap[std::make_pair(MBB, Val)] = VReg;
}
Register SwiftErrorValueTracking::getOrCreateVRegDefAt(
const Instruction *I, const MachineBasicBlock *MBB, const Value *Val) {
auto Key = PointerIntPair<const Instruction *, 1, bool>(I, true);
auto It = VRegDefUses.find(Key);
if (It != VRegDefUses.end())
return It->second;
auto &DL = MF->getDataLayout();
const TargetRegisterClass *RC = TLI->getRegClassFor(TLI->getPointerTy(DL));
Register VReg = MF->getRegInfo().createVirtualRegister(RC);
VRegDefUses[Key] = VReg;
setCurrentVReg(MBB, Val, VReg);
return VReg;
}
Register SwiftErrorValueTracking::getOrCreateVRegUseAt(
const Instruction *I, const MachineBasicBlock *MBB, const Value *Val) {
auto Key = PointerIntPair<const Instruction *, 1, bool>(I, false);
auto It = VRegDefUses.find(Key);
if (It != VRegDefUses.end())
return It->second;
Register VReg = getOrCreateVReg(MBB, Val);
VRegDefUses[Key] = VReg;
return VReg;
}
/// Set up SwiftErrorVals by going through the function. If the function has
/// swifterror argument, it will be the first entry.
void SwiftErrorValueTracking::setFunction(MachineFunction &mf) {
MF = &mf;
Fn = &MF->getFunction();
TLI = MF->getSubtarget().getTargetLowering();
TII = MF->getSubtarget().getInstrInfo();
if (!TLI->supportSwiftError())
return;
SwiftErrorVals.clear();
VRegDefMap.clear();
VRegUpwardsUse.clear();
VRegDefUses.clear();
SwiftErrorArg = nullptr;
// Check if function has a swifterror argument.
bool HaveSeenSwiftErrorArg = false;
for (Function::const_arg_iterator AI = Fn->arg_begin(), AE = Fn->arg_end();
AI != AE; ++AI)
if (AI->hasSwiftErrorAttr()) {
assert(!HaveSeenSwiftErrorArg &&
"Must have only one swifterror parameter");
(void)HaveSeenSwiftErrorArg; // silence warning.
HaveSeenSwiftErrorArg = true;
SwiftErrorArg = &*AI;
SwiftErrorVals.push_back(&*AI);
}
for (const auto &LLVMBB : *Fn)
for (const auto &Inst : LLVMBB) {
if (const AllocaInst *Alloca = dyn_cast<AllocaInst>(&Inst))
if (Alloca->isSwiftError())
SwiftErrorVals.push_back(Alloca);
}
}
bool SwiftErrorValueTracking::createEntriesInEntryBlock(DebugLoc DbgLoc) {
if (!TLI->supportSwiftError())
return false;
// We only need to do this when we have swifterror parameter or swifterror
// alloc.
if (SwiftErrorVals.empty())
return false;
MachineBasicBlock *MBB = &*MF->begin();
auto &DL = MF->getDataLayout();
auto const *RC = TLI->getRegClassFor(TLI->getPointerTy(DL));
bool Inserted = false;
for (const auto *SwiftErrorVal : SwiftErrorVals) {
// We will always generate a copy from the argument. It is always used at
// least by the 'return' of the swifterror.
if (SwiftErrorArg && SwiftErrorArg == SwiftErrorVal)
continue;
Register VReg = MF->getRegInfo().createVirtualRegister(RC);
// Assign Undef to Vreg. We construct MI directly to make sure it works
// with FastISel.
BuildMI(*MBB, MBB->getFirstNonPHI(), DbgLoc,
TII->get(TargetOpcode::IMPLICIT_DEF), VReg);
setCurrentVReg(MBB, SwiftErrorVal, VReg);
Inserted = true;
}
return Inserted;
}
/// Propagate swifterror values through the machine function CFG.
void SwiftErrorValueTracking::propagateVRegs() {
if (!TLI->supportSwiftError())
return;
// We only need to do this when we have swifterror parameter or swifterror
// alloc.
if (SwiftErrorVals.empty())
return;
// For each machine basic block in reverse post order.
ReversePostOrderTraversal<MachineFunction *> RPOT(MF);
for (MachineBasicBlock *MBB : RPOT) {
// For each swifterror value in the function.
for (const auto *SwiftErrorVal : SwiftErrorVals) {
auto Key = std::make_pair(MBB, SwiftErrorVal);
auto UUseIt = VRegUpwardsUse.find(Key);
auto VRegDefIt = VRegDefMap.find(Key);
bool UpwardsUse = UUseIt != VRegUpwardsUse.end();
Register UUseVReg = UpwardsUse ? UUseIt->second : Register();
bool DownwardDef = VRegDefIt != VRegDefMap.end();
assert(!(UpwardsUse && !DownwardDef) &&
"We can't have an upwards use but no downwards def");
// If there is no upwards exposed use and an entry for the swifterror in
// the def map for this value we don't need to do anything: We already
// have a downward def for this basic block.
if (!UpwardsUse && DownwardDef)
continue;
// Otherwise we either have an upwards exposed use vreg that we need to
// materialize or need to forward the downward def from predecessors.
// Check whether we have a single vreg def from all predecessors.
// Otherwise we need a phi.
SmallVector<std::pair<MachineBasicBlock *, Register>, 4> VRegs;
SmallSet<const MachineBasicBlock *, 8> Visited;
for (auto *Pred : MBB->predecessors()) {
if (!Visited.insert(Pred).second)
continue;
VRegs.push_back(std::make_pair(
Pred, getOrCreateVReg(Pred, SwiftErrorVal)));
if (Pred != MBB)
continue;
// We have a self-edge.
// If there was no upwards use in this basic block there is now one: the
// phi needs to use it self.
if (!UpwardsUse) {
UpwardsUse = true;
UUseIt = VRegUpwardsUse.find(Key);
assert(UUseIt != VRegUpwardsUse.end());
UUseVReg = UUseIt->second;
}
}
// We need a phi node if we have more than one predecessor with different
// downward defs.
bool needPHI =
VRegs.size() >= 1 &&
std::find_if(
VRegs.begin(), VRegs.end(),
[&](const std::pair<const MachineBasicBlock *, Register> &V)
-> bool { return V.second != VRegs[0].second; }) !=
VRegs.end();
// If there is no upwards exposed used and we don't need a phi just
// forward the swifterror vreg from the predecessor(s).
if (!UpwardsUse && !needPHI) {
assert(!VRegs.empty() &&
"No predecessors? The entry block should bail out earlier");
// Just forward the swifterror vreg from the predecessor(s).
setCurrentVReg(MBB, SwiftErrorVal, VRegs[0].second);
continue;
}
auto DLoc = isa<Instruction>(SwiftErrorVal)
? cast<Instruction>(SwiftErrorVal)->getDebugLoc()
: DebugLoc();
const auto *TII = MF->getSubtarget().getInstrInfo();
// If we don't need a phi create a copy to the upward exposed vreg.
if (!needPHI) {
assert(UpwardsUse);
assert(!VRegs.empty() &&
"No predecessors? Is the Calling Convention correct?");
Register DestReg = UUseVReg;
BuildMI(*MBB, MBB->getFirstNonPHI(), DLoc, TII->get(TargetOpcode::COPY),
DestReg)
.addReg(VRegs[0].second);
continue;
}
// We need a phi: if there is an upwards exposed use we already have a
// destination virtual register number otherwise we generate a new one.
auto &DL = MF->getDataLayout();
auto const *RC = TLI->getRegClassFor(TLI->getPointerTy(DL));
Register PHIVReg =
UpwardsUse ? UUseVReg : MF->getRegInfo().createVirtualRegister(RC);
MachineInstrBuilder PHI =
BuildMI(*MBB, MBB->getFirstNonPHI(), DLoc,
TII->get(TargetOpcode::PHI), PHIVReg);
for (auto BBRegPair : VRegs) {
PHI.addReg(BBRegPair.second).addMBB(BBRegPair.first);
}
// We did not have a definition in this block before: store the phi's vreg
// as this block downward exposed def.
if (!UpwardsUse)
setCurrentVReg(MBB, SwiftErrorVal, PHIVReg);
}
}
}
void SwiftErrorValueTracking::preassignVRegs(
MachineBasicBlock *MBB, BasicBlock::const_iterator Begin,
BasicBlock::const_iterator End) {
if (!TLI->supportSwiftError() || SwiftErrorVals.empty())
return;
// Iterator over instructions and assign vregs to swifterror defs and uses.
for (auto It = Begin; It != End; ++It) {
ImmutableCallSite CS(&*It);
if (CS) {
// A call-site with a swifterror argument is both use and def.
const Value *SwiftErrorAddr = nullptr;
for (auto &Arg : CS.args()) {
if (!Arg->isSwiftError())
continue;
// Use of swifterror.
assert(!SwiftErrorAddr && "Cannot have multiple swifterror arguments");
SwiftErrorAddr = &*Arg;
assert(SwiftErrorAddr->isSwiftError() &&
"Must have a swifterror value argument");
getOrCreateVRegUseAt(&*It, MBB, SwiftErrorAddr);
}
if (!SwiftErrorAddr)
continue;
// Def of swifterror.
getOrCreateVRegDefAt(&*It, MBB, SwiftErrorAddr);
// A load is a use.
} else if (const LoadInst *LI = dyn_cast<const LoadInst>(&*It)) {
const Value *V = LI->getOperand(0);
if (!V->isSwiftError())
continue;
getOrCreateVRegUseAt(LI, MBB, V);
// A store is a def.
} else if (const StoreInst *SI = dyn_cast<const StoreInst>(&*It)) {
const Value *SwiftErrorAddr = SI->getOperand(1);
if (!SwiftErrorAddr->isSwiftError())
continue;
// Def of swifterror.
getOrCreateVRegDefAt(&*It, MBB, SwiftErrorAddr);
// A return in a swiferror returning function is a use.
} else if (const ReturnInst *R = dyn_cast<const ReturnInst>(&*It)) {
const Function *F = R->getParent()->getParent();
if (!F->getAttributes().hasAttrSomewhere(Attribute::SwiftError))
continue;
getOrCreateVRegUseAt(R, MBB, SwiftErrorArg);
}
}
}