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

[Tom Stellard via llvm-commits]

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();

-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.
> +    }
> +  }
> +