f7d8336a2f
This patch is in preparation to enable setting the MachineInstr::MIFlag
flags, i.e. FrameSetup/FrameDestroy, on callee saved register
spill/reload instructions in prologue/epilogue. This eventually helps in
setting the prologue_end and epilogue_begin markers more accurately.
The DWARF Spec in "6.4 Call Frame Information" says:
The code that allocates space on the call frame stack and performs the
save
operation is called the subroutine’s prologue, and the code that
performs
the restore operation and deallocates the frame is called its epilogue.
which means the callee saved register spills and reloads are part of
prologue (a.k.a frame setup) and epilogue (a.k.a frame destruction),
respectively. And, IIUC, LLVM backend uses FrameSetup/FrameDestroy flags
to identify instructions that are part of call frame setup and
destruction.
In the trunk, while most targets consistently set
FrameSetup/FrameDestroy on save/restore call frame information (CFI)
instructions of callee saved registers, they do not consistently set
those flags on the actual callee saved register spill/reload
instructions.
I believe this patch provides a clean mechanism to set
FrameSetup/FrameDestroy flags on the actual callee saved register
spill/reload instructions as needed. And, by having default argument of
MachineInstr::NoFlags for Flags, this patch is a NFC.
With this patch, the targets have to just pass FrameSetup/FrameDestroy
flag to the storeRegToStackSlot/loadRegFromStackSlot calls from the
target derived spillCalleeSavedRegisters and restoreCalleeSavedRegisters
to set those flags on callee saved register spill/reload instructions.
Also, this patch makes it very easy to set the source line information
on callee saved register spill/reload instructions which is needed by
the DwarfDebug.cpp implementation to set prologue_end and epilogue_begin
markers more accurately.
As per DwarfDebug.cpp implementation:
prologue_end is the first known non-DBG_VALUE and non-FrameSetup
location
that marks the beginning of the function body
epilogue_begin is the first FrameDestroy location that has been seen in
the
epilogue basic block
With this patch, the targets have to just do the following to set the
source line information on callee saved register spill/reload
instructions, without hampering the LLVM's efforts to avoid adding
source line information on the artificial code generated by the
compiler.
<Foo>InstrInfo::storeRegToStackSlot() {
...
DebugLoc DL =
Flags & MachineInstr::FrameSetup ? DebugLoc() : MBB.findDebugLoc(I);
...
}
<Foo>InstrInfo::loadRegFromStackSlot() {
...
DebugLoc DL =
Flags & MachineInstr::FrameDestroy ? MBB.findDebugLoc(I) : DebugLoc();
...
}
While I understand this patch would break out-of-tree backend builds, I
think it is in the right direction.
One immediate use case that can benefit from this patch is fixing
#120553 becomes simpler.
95 lines
4.1 KiB
C++
95 lines
4.1 KiB
C++
//===-- XCoreInstrInfo.h - XCore Instruction Information --------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file contains the XCore implementation of the TargetInstrInfo class.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_LIB_TARGET_XCORE_XCOREINSTRINFO_H
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#define LLVM_LIB_TARGET_XCORE_XCOREINSTRINFO_H
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#include "XCoreRegisterInfo.h"
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#include "llvm/CodeGen/TargetInstrInfo.h"
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#define GET_INSTRINFO_HEADER
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#include "XCoreGenInstrInfo.inc"
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namespace llvm {
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class XCoreInstrInfo : public XCoreGenInstrInfo {
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const XCoreRegisterInfo RI;
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virtual void anchor();
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public:
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XCoreInstrInfo();
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/// getRegisterInfo - TargetInstrInfo is a superset of MRegister info. As
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/// such, whenever a client has an instance of instruction info, it should
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/// always be able to get register info as well (through this method).
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///
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const TargetRegisterInfo &getRegisterInfo() const { return RI; }
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/// isLoadFromStackSlot - If the specified machine instruction is a direct
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/// load from a stack slot, return the virtual or physical register number of
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/// the destination along with the FrameIndex of the loaded stack slot. If
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/// not, return 0. This predicate must return 0 if the instruction has
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/// any side effects other than loading from the stack slot.
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Register isLoadFromStackSlot(const MachineInstr &MI,
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int &FrameIndex) const override;
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/// isStoreToStackSlot - If the specified machine instruction is a direct
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/// store to a stack slot, return the virtual or physical register number of
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/// the source reg along with the FrameIndex of the loaded stack slot. If
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/// not, return 0. This predicate must return 0 if the instruction has
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/// any side effects other than storing to the stack slot.
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Register isStoreToStackSlot(const MachineInstr &MI,
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int &FrameIndex) const override;
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bool analyzeBranch(MachineBasicBlock &MBB, MachineBasicBlock *&TBB,
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MachineBasicBlock *&FBB,
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SmallVectorImpl<MachineOperand> &Cond,
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bool AllowModify) const override;
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unsigned insertBranch(MachineBasicBlock &MBB, MachineBasicBlock *TBB,
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MachineBasicBlock *FBB, ArrayRef<MachineOperand> Cond,
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const DebugLoc &DL,
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int *BytesAdded = nullptr) const override;
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unsigned removeBranch(MachineBasicBlock &MBB,
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int *BytesRemoved = nullptr) const override;
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void copyPhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator I,
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const DebugLoc &DL, MCRegister DestReg, MCRegister SrcReg,
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bool KillSrc, bool RenamableDest = false,
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bool RenamableSrc = false) const override;
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void storeRegToStackSlot(
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MachineBasicBlock &MBB, MachineBasicBlock::iterator MI, Register SrcReg,
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bool isKill, int FrameIndex, const TargetRegisterClass *RC,
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const TargetRegisterInfo *TRI, Register VReg,
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MachineInstr::MIFlag Flags = MachineInstr::NoFlags) const override;
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void loadRegFromStackSlot(
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MachineBasicBlock &MBB, MachineBasicBlock::iterator MI, Register DestReg,
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int FrameIndex, const TargetRegisterClass *RC,
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const TargetRegisterInfo *TRI, Register VReg,
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MachineInstr::MIFlag Flags = MachineInstr::NoFlags) const override;
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bool reverseBranchCondition(
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SmallVectorImpl<MachineOperand> &Cond) const override;
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// Emit code before MBBI to load immediate value into physical register Reg.
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// Returns an iterator to the new instruction.
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MachineBasicBlock::iterator loadImmediate(MachineBasicBlock &MBB,
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MachineBasicBlock::iterator MI,
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unsigned Reg, uint64_t Value) const;
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};
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}
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#endif
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