6c412b6c6f
In [1], a few new insns are proposed to expand BPF ISA to
. fixing the limitation of existing insn (e.g., 16bit jmp offset)
. adding new insns which may improve code quality
(sign_ext_ld, sign_ext_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 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.,
13: 06 00 00 00 9b cd 00 00 gotol +0xcd9b <LBB0_6619>
Eduard is working on to add 'st' insn to cpu=v4.
A list of llc flags:
disable-ldsx, disable-movsx, disable-bswap,
disable-sdiv-smod, disable-gotol
can be used to disable a particular insn for cpu v4.
For example, user can do:
llc -march=bpf -mcpu=v4 -disable-movsx t.ll
to enable cpu v4 without movsx insns.
References:
[1] https://lore.kernel.org/bpf/4bfe98be-5333-1c7e-2f6d-42486c8ec039@meta.com/
Differential Revision: https://reviews.llvm.org/D144829
92 lines
2.8 KiB
C++
92 lines
2.8 KiB
C++
//===-- BPFSubtarget.cpp - BPF Subtarget Information ----------------------===//
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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 implements the BPF specific subclass of TargetSubtargetInfo.
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//
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//===----------------------------------------------------------------------===//
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#include "BPFSubtarget.h"
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#include "BPF.h"
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#include "llvm/MC/TargetRegistry.h"
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#include "llvm/TargetParser/Host.h"
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using namespace llvm;
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#define DEBUG_TYPE "bpf-subtarget"
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#define GET_SUBTARGETINFO_TARGET_DESC
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#define GET_SUBTARGETINFO_CTOR
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#include "BPFGenSubtargetInfo.inc"
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static cl::opt<bool> Disable_ldsx("disable-ldsx", cl::Hidden, cl::init(false),
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cl::desc("Disable ldsx insns"));
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static cl::opt<bool> Disable_movsx("disable-movsx", cl::Hidden, cl::init(false),
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cl::desc("Disable movsx insns"));
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static cl::opt<bool> Disable_bswap("disable-bswap", cl::Hidden, cl::init(false),
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cl::desc("Disable bswap insns"));
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static cl::opt<bool> Disable_sdiv_smod("disable-sdiv-smod", cl::Hidden,
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cl::init(false), cl::desc("Disable sdiv/smod insns"));
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static cl::opt<bool> Disable_gotol("disable-gotol", cl::Hidden, cl::init(false),
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cl::desc("Disable gotol insn"));
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void BPFSubtarget::anchor() {}
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BPFSubtarget &BPFSubtarget::initializeSubtargetDependencies(StringRef CPU,
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StringRef FS) {
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initializeEnvironment();
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initSubtargetFeatures(CPU, FS);
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ParseSubtargetFeatures(CPU, /*TuneCPU*/ CPU, FS);
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return *this;
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}
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void BPFSubtarget::initializeEnvironment() {
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HasJmpExt = false;
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HasJmp32 = false;
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HasAlu32 = false;
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UseDwarfRIS = false;
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HasLdsx = false;
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HasMovsx = false;
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HasBswap = false;
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HasSdivSmod = false;
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HasGotol = false;
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}
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void BPFSubtarget::initSubtargetFeatures(StringRef CPU, StringRef FS) {
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if (CPU == "probe")
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CPU = sys::detail::getHostCPUNameForBPF();
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if (CPU == "generic" || CPU == "v1")
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return;
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if (CPU == "v2") {
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HasJmpExt = true;
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return;
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}
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if (CPU == "v3") {
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HasJmpExt = true;
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HasJmp32 = true;
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HasAlu32 = true;
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return;
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}
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if (CPU == "v4") {
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HasJmpExt = true;
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HasJmp32 = true;
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HasAlu32 = true;
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HasLdsx = !Disable_ldsx;
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HasMovsx = !Disable_movsx;
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HasBswap = !Disable_bswap;
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HasSdivSmod = !Disable_sdiv_smod;
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HasGotol = !Disable_gotol;
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return;
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}
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}
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BPFSubtarget::BPFSubtarget(const Triple &TT, const std::string &CPU,
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const std::string &FS, const TargetMachine &TM)
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: BPFGenSubtargetInfo(TT, CPU, /*TuneCPU*/ CPU, FS),
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FrameLowering(initializeSubtargetDependencies(CPU, FS)),
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TLInfo(TM, *this) {}
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