[PATCH] D144829: [WIP][BPF] Add a few new insns under cpu=v4

[Yonghong Song via Phabricator via llvm-commits]

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In [1], a few new insns are proposed to exgend BPF ISA to

  . fixing the limitation of existing insn (e.g., 16bit jmp offset)
  . adding new insns which may improve code quality (sext_ld, sext_mov, st) 
  . feature complete (sdiv, smod)
  . better user experience (bswap)

This patch implemented insn encoding for

  . sign-extended load
  . sign-extended mov 
  . sdiv/smod
  . bswap insns
  . unconditional jump with 32bit offset

The encoding for sign-extended load/mov, sdiv/smod are followed by
proposal in [1] except a couple of changes like sign-extended load
does not really have alu32 mode, and sign-extend mov only supports
`dst_reg<-(sign extend)src_reg` format. I will update the proposal
in bpf mailing list later.

The new bswap insns are generated under cpu=v4 for __builtin_bswap.
For cpu=v3 or earlier, for __builtin_bswap, be or le insns are generated
which is not intuitive for the user.

To support 32-bit branch offset, a 32-bit ja (JMPL) insn is implemented.
For conditional branch which is beyond 16-bit offset, llvm will do
some transformation 'cond_jmp' -> 'cond_jmp + jmpl' to simulate 32bit
conditional jmp. See BPFMIPeephole.cpp for details. The algorithm is
hueristic based. I have tested bpf selftest pyperf600 with unroll account
600 which can indeed generate 32-bit jump insn, e.g.,

  14:       06 00 00 00 27 ef 00 00 gotol +0xef27 <LBB0_78200+0xffffffffffd9fd88>

In the above, need to investigate why llvm-objdump prints out 
'<LBB0_78200+0xffffffffffd9fd88>', probably due to my introduction
of BPF specific fixup kinds.

Eduard is working on to add 'st' insn to cpu=v4.

This patch is in WIP stage since I need to:

  (1). investigate the above '<LBB0_78200+0xffffffffffd9fd88>' print,
  (2). add verifier support for the above insns.

References:

  [1] https://lore.kernel.org/bpf/01515302-c37d-2ee5-c950-2f556a4caad0@meta.com/


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D144829

Files:
  clang/lib/Basic/Targets/BPF.cpp
  clang/lib/Basic/Targets/BPF.h
  llvm/lib/Target/BPF/BPF.td
  llvm/lib/Target/BPF/BPFISelDAGToDAG.cpp
  llvm/lib/Target/BPF/BPFISelLowering.cpp
  llvm/lib/Target/BPF/BPFInstrFormats.td
  llvm/lib/Target/BPF/BPFInstrInfo.td
  llvm/lib/Target/BPF/BPFMIPeephole.cpp
  llvm/lib/Target/BPF/BPFSubtarget.cpp
  llvm/lib/Target/BPF/BPFSubtarget.h
  llvm/lib/Target/BPF/Disassembler/BPFDisassembler.cpp
  llvm/lib/Target/BPF/MCTargetDesc/BPFAsmBackend.cpp
  llvm/lib/Target/BPF/MCTargetDesc/BPFInstPrinter.cpp
  llvm/lib/Target/BPF/MCTargetDesc/BPFMCCodeEmitter.cpp
  llvm/lib/Target/BPF/MCTargetDesc/BPFMCFixups.h
  llvm/test/CodeGen/BPF/bswap.ll
  llvm/test/CodeGen/BPF/sdiv_smod.ll
  llvm/test/CodeGen/BPF/sext_ld.ll
  llvm/test/CodeGen/BPF/sext_mov.ll

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