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
60 lines
2.0 KiB
C++
60 lines
2.0 KiB
C++
//===--- BPF.cpp - Implement BPF target feature support -------------------===//
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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 BPF TargetInfo objects.
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//
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//===----------------------------------------------------------------------===//
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#include "BPF.h"
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#include "Targets.h"
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#include "clang/Basic/MacroBuilder.h"
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#include "clang/Basic/TargetBuiltins.h"
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#include "llvm/ADT/StringRef.h"
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using namespace clang;
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using namespace clang::targets;
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static constexpr Builtin::Info BuiltinInfo[] = {
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#define BUILTIN(ID, TYPE, ATTRS) \
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{#ID, TYPE, ATTRS, nullptr, HeaderDesc::NO_HEADER, ALL_LANGUAGES},
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#include "clang/Basic/BuiltinsBPF.def"
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};
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void BPFTargetInfo::getTargetDefines(const LangOptions &Opts,
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MacroBuilder &Builder) const {
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Builder.defineMacro("__bpf__");
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Builder.defineMacro("__BPF__");
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}
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static constexpr llvm::StringLiteral ValidCPUNames[] = {"generic", "v1", "v2",
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"v3", "v4", "probe"};
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bool BPFTargetInfo::isValidCPUName(StringRef Name) const {
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return llvm::is_contained(ValidCPUNames, Name);
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}
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void BPFTargetInfo::fillValidCPUList(SmallVectorImpl<StringRef> &Values) const {
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Values.append(std::begin(ValidCPUNames), std::end(ValidCPUNames));
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}
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ArrayRef<Builtin::Info> BPFTargetInfo::getTargetBuiltins() const {
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return llvm::ArrayRef(BuiltinInfo,
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clang::BPF::LastTSBuiltin - Builtin::FirstTSBuiltin);
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}
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bool BPFTargetInfo::handleTargetFeatures(std::vector<std::string> &Features,
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DiagnosticsEngine &Diags) {
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for (const auto &Feature : Features) {
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if (Feature == "+alu32") {
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HasAlu32 = true;
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}
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}
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return true;
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}
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