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llvm-project/llvm/lib/Target/SystemZ/SystemZSelectionDAGInfo.cpp

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//===-- SystemZSelectionDAGInfo.cpp - SystemZ SelectionDAG Info -----------===//
//
// 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 file implements the SystemZSelectionDAGInfo class.
//
//===----------------------------------------------------------------------===//
#include "SystemZTargetMachine.h"
#include "llvm/CodeGen/SelectionDAG.h"
using namespace llvm;
#define DEBUG_TYPE "systemz-selectiondag-info"
// Decide whether it is best to use a loop or straight-line code for
// a block operation of Size bytes with source address Src and destination
// address Dest. Sequence is the opcode to use for straight-line code
// (such as MVC) and Loop is the opcode to use for loops (such as MVC_LOOP).
// Return the chain for the completed operation.
static SDValue emitMemMem(SelectionDAG &DAG, const SDLoc &DL, unsigned Sequence,
unsigned Loop, SDValue Chain, SDValue Dst,
SDValue Src, uint64_t Size) {
EVT PtrVT = Src.getValueType();
// The heuristic we use is to prefer loops for anything that would
// require 7 or more MVCs. With these kinds of sizes there isn't
// much to choose between straight-line code and looping code,
// since the time will be dominated by the MVCs themselves.
// However, the loop has 4 or 5 instructions (depending on whether
// the base addresses can be proved equal), so there doesn't seem
// much point using a loop for 5 * 256 bytes or fewer. Anything in
// the range (5 * 256, 6 * 256) will need another instruction after
// the loop, so it doesn't seem worth using a loop then either.
// The next value up, 6 * 256, can be implemented in the same
// number of straight-line MVCs as 6 * 256 - 1.
if (Size > 6 * 256)
return DAG.getNode(Loop, DL, MVT::Other, Chain, Dst, Src,
DAG.getConstant(Size, DL, PtrVT),
DAG.getConstant(Size / 256, DL, PtrVT));
return DAG.getNode(Sequence, DL, MVT::Other, Chain, Dst, Src,
DAG.getConstant(Size, DL, PtrVT));
}
SDValue SystemZSelectionDAGInfo::EmitTargetCodeForMemcpy(
SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Dst, SDValue Src,
SDValue Size, Align Alignment, bool IsVolatile, bool AlwaysInline,
MachinePointerInfo DstPtrInfo, MachinePointerInfo SrcPtrInfo) const {
if (IsVolatile)
return SDValue();
if (auto *CSize = dyn_cast<ConstantSDNode>(Size))
return emitMemMem(DAG, DL, SystemZISD::MVC, SystemZISD::MVC_LOOP,
Chain, Dst, Src, CSize->getZExtValue());
return SDValue();
}
// Handle a memset of 1, 2, 4 or 8 bytes with the operands given by
// Chain, Dst, ByteVal and Size. These cases are expected to use
// MVI, MVHHI, MVHI and MVGHI respectively.
static SDValue memsetStore(SelectionDAG &DAG, const SDLoc &DL, SDValue Chain,
SDValue Dst, uint64_t ByteVal, uint64_t Size,
unsigned Align, MachinePointerInfo DstPtrInfo) {
uint64_t StoreVal = ByteVal;
for (unsigned I = 1; I < Size; ++I)
StoreVal |= ByteVal << (I * 8);
return DAG.getStore(
Chain, DL, DAG.getConstant(StoreVal, DL, MVT::getIntegerVT(Size * 8)),
Dst, DstPtrInfo, Align);
}
SDValue SystemZSelectionDAGInfo::EmitTargetCodeForMemset(
SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Dst,
SDValue Byte, SDValue Size, Align Alignment, bool IsVolatile,
MachinePointerInfo DstPtrInfo) const {
EVT PtrVT = Dst.getValueType();
if (IsVolatile)
return SDValue();
if (auto *CSize = dyn_cast<ConstantSDNode>(Size)) {
uint64_t Bytes = CSize->getZExtValue();
if (Bytes == 0)
return SDValue();
if (auto *CByte = dyn_cast<ConstantSDNode>(Byte)) {
// Handle cases that can be done using at most two of
// MVI, MVHI, MVHHI and MVGHI. The latter two can only be
// used if ByteVal is all zeros or all ones; in other casees,
// we can move at most 2 halfwords.
uint64_t ByteVal = CByte->getZExtValue();
if (ByteVal == 0 || ByteVal == 255 ?
Bytes <= 16 && countPopulation(Bytes) <= 2 :
Bytes <= 4) {
unsigned Size1 = Bytes == 16 ? 8 : 1 << findLastSet(Bytes);
unsigned Size2 = Bytes - Size1;
SDValue Chain1 = memsetStore(DAG, DL, Chain, Dst, ByteVal, Size1,
Alignment.value(), DstPtrInfo);
if (Size2 == 0)
return Chain1;
Dst = DAG.getNode(ISD::ADD, DL, PtrVT, Dst,
DAG.getConstant(Size1, DL, PtrVT));
DstPtrInfo = DstPtrInfo.getWithOffset(Size1);
SDValue Chain2 = memsetStore(
DAG, DL, Chain, Dst, ByteVal, Size2,
std::min((unsigned)Alignment.value(), Size1), DstPtrInfo);
return DAG.getNode(ISD::TokenFactor, DL, MVT::Other, Chain1, Chain2);
}
} else {
// Handle one and two bytes using STC.
if (Bytes <= 2) {
SDValue Chain1 =
DAG.getStore(Chain, DL, Byte, Dst, DstPtrInfo, Alignment);
if (Bytes == 1)
return Chain1;
SDValue Dst2 = DAG.getNode(ISD::ADD, DL, PtrVT, Dst,
DAG.getConstant(1, DL, PtrVT));
SDValue Chain2 = DAG.getStore(Chain, DL, Byte, Dst2,
DstPtrInfo.getWithOffset(1), Align(1));
return DAG.getNode(ISD::TokenFactor, DL, MVT::Other, Chain1, Chain2);
}
}
assert(Bytes >= 2 && "Should have dealt with 0- and 1-byte cases already");
// Handle the special case of a memset of 0, which can use XC.
auto *CByte = dyn_cast<ConstantSDNode>(Byte);
if (CByte && CByte->getZExtValue() == 0)
return emitMemMem(DAG, DL, SystemZISD::XC, SystemZISD::XC_LOOP,
Chain, Dst, Dst, Bytes);
// Copy the byte to the first location and then use MVC to copy
// it to the rest.
Chain = DAG.getStore(Chain, DL, Byte, Dst, DstPtrInfo, Alignment);
SDValue DstPlus1 = DAG.getNode(ISD::ADD, DL, PtrVT, Dst,
DAG.getConstant(1, DL, PtrVT));
return emitMemMem(DAG, DL, SystemZISD::MVC, SystemZISD::MVC_LOOP,
Chain, DstPlus1, Dst, Bytes - 1);
}
return SDValue();
}
// Use CLC to compare [Src1, Src1 + Size) with [Src2, Src2 + Size),
// deciding whether to use a loop or straight-line code.
static SDValue emitCLC(SelectionDAG &DAG, const SDLoc &DL, SDValue Chain,
SDValue Src1, SDValue Src2, uint64_t Size) {
SDVTList VTs = DAG.getVTList(MVT::i32, MVT::Other);
EVT PtrVT = Src1.getValueType();
// A two-CLC sequence is a clear win over a loop, not least because it
// needs only one branch. A three-CLC sequence needs the same number
// of branches as a loop (i.e. 2), but is shorter. That brings us to
// lengths greater than 768 bytes. It seems relatively likely that
// a difference will be found within the first 768 bytes, so we just
// optimize for the smallest number of branch instructions, in order
// to avoid polluting the prediction buffer too much. A loop only ever
// needs 2 branches, whereas a straight-line sequence would need 3 or more.
if (Size > 3 * 256)
return DAG.getNode(SystemZISD::CLC_LOOP, DL, VTs, Chain, Src1, Src2,
DAG.getConstant(Size, DL, PtrVT),
DAG.getConstant(Size / 256, DL, PtrVT));
return DAG.getNode(SystemZISD::CLC, DL, VTs, Chain, Src1, Src2,
DAG.getConstant(Size, DL, PtrVT));
}
// Convert the current CC value into an integer that is 0 if CC == 0,
// greater than zero if CC == 1 and less than zero if CC >= 2.
// The sequence starts with IPM, which puts CC into bits 29 and 28
// of an integer and clears bits 30 and 31.
static SDValue addIPMSequence(const SDLoc &DL, SDValue CCReg,
SelectionDAG &DAG) {
SDValue IPM = DAG.getNode(SystemZISD::IPM, DL, MVT::i32, CCReg);
SDValue SHL = DAG.getNode(ISD::SHL, DL, MVT::i32, IPM,
DAG.getConstant(30 - SystemZ::IPM_CC, DL, MVT::i32));
SDValue SRA = DAG.getNode(ISD::SRA, DL, MVT::i32, SHL,
DAG.getConstant(30, DL, MVT::i32));
return SRA;
}
std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForMemcmp(
SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Src1,
SDValue Src2, SDValue Size, MachinePointerInfo Op1PtrInfo,
MachinePointerInfo Op2PtrInfo) const {
if (auto *CSize = dyn_cast<ConstantSDNode>(Size)) {
uint64_t Bytes = CSize->getZExtValue();
assert(Bytes > 0 && "Caller should have handled 0-size case");
// Swap operands to invert CC == 1 vs. CC == 2 cases.
SDValue CCReg = emitCLC(DAG, DL, Chain, Src2, Src1, Bytes);
Chain = CCReg.getValue(1);
return std::make_pair(addIPMSequence(DL, CCReg, DAG), Chain);
}
return std::make_pair(SDValue(), SDValue());
}
std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForMemchr(
SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Src,
SDValue Char, SDValue Length, MachinePointerInfo SrcPtrInfo) const {
// Use SRST to find the character. End is its address on success.
EVT PtrVT = Src.getValueType();
SDVTList VTs = DAG.getVTList(PtrVT, MVT::i32, MVT::Other);
Length = DAG.getZExtOrTrunc(Length, DL, PtrVT);
Char = DAG.getZExtOrTrunc(Char, DL, MVT::i32);
Char = DAG.getNode(ISD::AND, DL, MVT::i32, Char,
DAG.getConstant(255, DL, MVT::i32));
SDValue Limit = DAG.getNode(ISD::ADD, DL, PtrVT, Src, Length);
SDValue End = DAG.getNode(SystemZISD::SEARCH_STRING, DL, VTs, Chain,
Limit, Src, Char);
SDValue CCReg = End.getValue(1);
Chain = End.getValue(2);
// Now select between End and null, depending on whether the character
// was found.
SDValue Ops[] = {
End, DAG.getConstant(0, DL, PtrVT),
DAG.getTargetConstant(SystemZ::CCMASK_SRST, DL, MVT::i32),
DAG.getTargetConstant(SystemZ::CCMASK_SRST_FOUND, DL, MVT::i32), CCReg};
End = DAG.getNode(SystemZISD::SELECT_CCMASK, DL, PtrVT, Ops);
return std::make_pair(End, Chain);
}
std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForStrcpy(
SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Dest,
SDValue Src, MachinePointerInfo DestPtrInfo, MachinePointerInfo SrcPtrInfo,
bool isStpcpy) const {
SDVTList VTs = DAG.getVTList(Dest.getValueType(), MVT::Other);
SDValue EndDest = DAG.getNode(SystemZISD::STPCPY, DL, VTs, Chain, Dest, Src,
DAG.getConstant(0, DL, MVT::i32));
return std::make_pair(isStpcpy ? EndDest : Dest, EndDest.getValue(1));
}
std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForStrcmp(
SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Src1,
SDValue Src2, MachinePointerInfo Op1PtrInfo,
MachinePointerInfo Op2PtrInfo) const {
SDVTList VTs = DAG.getVTList(Src1.getValueType(), MVT::i32, MVT::Other);
// Swap operands to invert CC == 1 vs. CC == 2 cases.
SDValue Unused = DAG.getNode(SystemZISD::STRCMP, DL, VTs, Chain, Src2, Src1,
DAG.getConstant(0, DL, MVT::i32));
SDValue CCReg = Unused.getValue(1);
Chain = Unused.getValue(2);
return std::make_pair(addIPMSequence(DL, CCReg, DAG), Chain);
}
// Search from Src for a null character, stopping once Src reaches Limit.
// Return a pair of values, the first being the number of nonnull characters
// and the second being the out chain.
//
// This can be used for strlen by setting Limit to 0.
static std::pair<SDValue, SDValue> getBoundedStrlen(SelectionDAG &DAG,
const SDLoc &DL,
SDValue Chain, SDValue Src,
SDValue Limit) {
EVT PtrVT = Src.getValueType();
SDVTList VTs = DAG.getVTList(PtrVT, MVT::i32, MVT::Other);
SDValue End = DAG.getNode(SystemZISD::SEARCH_STRING, DL, VTs, Chain,
Limit, Src, DAG.getConstant(0, DL, MVT::i32));
Chain = End.getValue(2);
SDValue Len = DAG.getNode(ISD::SUB, DL, PtrVT, End, Src);
return std::make_pair(Len, Chain);
}
std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForStrlen(
SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Src,
MachinePointerInfo SrcPtrInfo) const {
EVT PtrVT = Src.getValueType();
return getBoundedStrlen(DAG, DL, Chain, Src, DAG.getConstant(0, DL, PtrVT));
}
std::pair<SDValue, SDValue> SystemZSelectionDAGInfo::EmitTargetCodeForStrnlen(
SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Src,
SDValue MaxLength, MachinePointerInfo SrcPtrInfo) const {
EVT PtrVT = Src.getValueType();
MaxLength = DAG.getZExtOrTrunc(MaxLength, DL, PtrVT);
SDValue Limit = DAG.getNode(ISD::ADD, DL, PtrVT, Src, MaxLength);
return getBoundedStrlen(DAG, DL, Chain, Src, Limit);
}
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