[llvm] r276875 - [GlobalISel] Introduce an instruction selector.

[Ahmed Bougacha via llvm-commits]

On Wed, Jul 27, 2016 at 5:41 PM, Tom Stellard <tom at stellard.net> wrote:
> On Wed, Jul 27, 2016 at 02:31:56PM -0000, Ahmed Bougacha via llvm-commits wrote:
>> Author: ab
>> Date: Wed Jul 27 09:31:55 2016
>> New Revision: 276875
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=276875&view=rev
>> Log:
>> [GlobalISel] Introduce an instruction selector.
>>
>> And implement it for AArch64, supporting x/w ADD/OR.
>>
>> Differential Revision: https://reviews.llvm.org/D22373
>>
>
> <snip>
>
>>
>> Added: llvm/trunk/lib/CodeGen/GlobalISel/InstructionSelect.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/GlobalISel/InstructionSelect.cpp?rev=276875&view=auto
>> ==============================================================================
>> --- llvm/trunk/lib/CodeGen/GlobalISel/InstructionSelect.cpp (added)
>> +++ llvm/trunk/lib/CodeGen/GlobalISel/InstructionSelect.cpp Wed Jul 27 09:31:55 2016
>> @@ -0,0 +1,99 @@
>> +//===- llvm/CodeGen/GlobalISel/InstructionSelect.cpp - InstructionSelect ---==//
>> +//
>> +//                     The LLVM Compiler Infrastructure
>> +//
>> +// This file is distributed under the University of Illinois Open Source
>> +// License. See LICENSE.TXT for details.
>> +//
>> +//===----------------------------------------------------------------------===//
>> +/// \file
>> +/// This file implements the InstructionSelect class.
>> +//===----------------------------------------------------------------------===//
>> +
>> +#include "llvm/CodeGen/GlobalISel/InstructionSelect.h"
>> +#include "llvm/ADT/PostOrderIterator.h"
>> +#include "llvm/ADT/Twine.h"
>> +#include "llvm/CodeGen/GlobalISel/InstructionSelector.h"
>> +#include "llvm/CodeGen/MachineRegisterInfo.h"
>> +#include "llvm/IR/Function.h"
>> +#include "llvm/Support/CommandLine.h"
>> +#include "llvm/Support/Debug.h"
>> +#include "llvm/Target/TargetSubtargetInfo.h"
>> +
>> +#define DEBUG_TYPE "instruction-select"
>> +
>> +using namespace llvm;
>> +
>> +char InstructionSelect::ID = 0;
>> +INITIALIZE_PASS(InstructionSelect, DEBUG_TYPE,
>> +                "Select target instructions out of generic instructions",
>> +                false, false);
>> +
>> +InstructionSelect::InstructionSelect() : MachineFunctionPass(ID) {
>> +  initializeInstructionSelectPass(*PassRegistry::getPassRegistry());
>> +}
>> +
>> +static void reportSelectionError(const MachineInstr &MI, const Twine &Message) {
>> +  const MachineFunction &MF = *MI.getParent()->getParent();
>> +  std::string ErrStorage;
>> +  raw_string_ostream Err(ErrStorage);
>> +  Err << Message << ":\nIn function: " << MF.getName() << '\n' << MI << '\n';
>> +  report_fatal_error(Err.str());
>> +}
>> +
>> +bool InstructionSelect::runOnMachineFunction(MachineFunction &MF) {
>> +  DEBUG(dbgs() << "Selecting function: " << MF.getName() << '\n');
>> +
>> +  const InstructionSelector *ISel = MF.getSubtarget().getInstructionSelector();
>> +  assert(ISel && "Cannot work without InstructionSelector");
>> +
>> +  // FIXME: freezeReservedRegs is now done in IRTranslator, but there are many
>> +  // other MF/MFI fields we need to initialize.
>> +
>> +#ifndef NDEBUG
>> +  // FIXME: We could introduce new blocks and will need to fix the outer loop.
>> +  // Until then, keep track of the number of blocks to assert that we don't.
>> +  const size_t NumBlocks = MF.size();
>> +#endif
>> +
>> +  for (MachineBasicBlock *MBB : post_order(&MF)) {
>> +    for (MachineBasicBlock::reverse_iterator MII = MBB->rbegin(),
>> +                                             End = MBB->rend();
>> +         MII != End;) {
>> +      MachineInstr &MI = *MII++;
>
> I'm getting an assertion failure from the above loop.
>
> llc: ../include/llvm/ADT/ilist.h:244: llvm::ilist_iterator<NodeTy>&
> llvm::ilist_iterator<NodeTy>::operator--() [with NodeTy =
> llvm::MachineInstr]: Assertion `NodePtr && "--'d off the beginning of an
> ilist!"' failed.
>
>
> This is when I try to insert a new instruction and erase the old one,
> in my select() implementation.  For example:
>
> BuildMI(*BB, &I, DL, TII.get(AMDGPU::FLAT_STORE_DWORD))
>           .addOperand(I.getOperand(1))
>           .addOperand(I.getOperand(0))
>           .addImm(0)
>           .addImm(0)
>           .addImm(0);
>
> I.eraseFromParent();

Ah, let me try that out in AArch64.  I also want to dump all inserted
instructions; I'll do both.

-Ahmed

> -Tom
>
>
>
>> +      DEBUG(dbgs() << "Selecting: " << MI << '\n');
>> +      if (!ISel->select(MI))
>> +        reportSelectionError(MI, "Cannot select");
>> +      // FIXME: It would be nice to dump all inserted instructions.  It's not
>> +      // obvious how, esp. considering select() can insert after MI.
>> +    }
>> +  }
>> +