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d0f29b816e
Same dangling probes are redundant since they all have the same semantic that is to rely on the counts inference tool to get reasonable count for the same original block. Therefore, there's no need to keep multiple copies of them. I've seen jump threading created tons of redundant dangling probes that slowed down the compiler dramatically. Other optimization passes can also result in redundant probes though without an observed impact so far. This change removes block-wise redundant dangling probes specifically introduced by jump threading. To support removing redundant dangling probes caused by all other passes, a final function-wise deduplication is also added. An 18% size win of the .pseudo_probe section was seen for SPEC2017. No performance difference was observed. Differential Revision: https://reviews.llvm.org/D97482
100 lines
3.0 KiB
C++
100 lines
3.0 KiB
C++
//===- PseudoProbe.h - Pseudo Probe IR Helpers ------------------*- C++ -*-===//
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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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// Pseudo probe IR intrinsic and dwarf discriminator manipulation routines.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_IR_PSEUDOPROBE_H
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#define LLVM_IR_PSEUDOPROBE_H
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#include "llvm/ADT/Optional.h"
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#include <cassert>
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#include <cstdint>
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#include <limits>
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namespace llvm {
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class Instruction;
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class BasicBlock;
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constexpr const char *PseudoProbeDescMetadataName = "llvm.pseudo_probe_desc";
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enum class PseudoProbeType { Block = 0, IndirectCall, DirectCall };
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enum class PseudoProbeAttributes {
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Reserved = 0x1, // Reserved for future use.
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Dangling = 0x2, // The probe is dangling.
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};
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// The saturated distrution factor representing 100% for block probes.
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constexpr static uint64_t PseudoProbeFullDistributionFactor =
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std::numeric_limits<uint64_t>::max();
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struct PseudoProbeDwarfDiscriminator {
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public:
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// The following APIs encodes/decodes per-probe information to/from a
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// 32-bit integer which is organized as:
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// [2:0] - 0x7, this is reserved for regular discriminator,
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// see DWARF discriminator encoding rule
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// [18:3] - probe id
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// [25:19] - probe distribution factor
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// [28:26] - probe type, see PseudoProbeType
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// [31:29] - reserved for probe attributes
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static uint32_t packProbeData(uint32_t Index, uint32_t Type, uint32_t Flags,
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uint32_t Factor) {
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assert(Index <= 0xFFFF && "Probe index too big to encode, exceeding 2^16");
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assert(Type <= 0x7 && "Probe type too big to encode, exceeding 7");
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assert(Flags <= 0x7);
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assert(Factor <= 100 &&
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"Probe distribution factor too big to encode, exceeding 100");
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return (Index << 3) | (Factor << 19) | (Type << 26) | 0x7;
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}
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static uint32_t extractProbeIndex(uint32_t Value) {
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return (Value >> 3) & 0xFFFF;
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}
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static uint32_t extractProbeType(uint32_t Value) {
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return (Value >> 26) & 0x7;
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}
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static uint32_t extractProbeAttributes(uint32_t Value) {
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return (Value >> 29) & 0x7;
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}
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static uint32_t extractProbeFactor(uint32_t Value) {
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return (Value >> 19) & 0x7F;
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}
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// The saturated distrution factor representing 100% for callsites.
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constexpr static uint8_t FullDistributionFactor = 100;
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};
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struct PseudoProbe {
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uint32_t Id;
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uint32_t Type;
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uint32_t Attr;
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float Factor;
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bool isDangling() const {
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return Attr & (uint32_t)PseudoProbeAttributes::Dangling;
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}
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};
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Optional<PseudoProbe> extractProbe(const Instruction &Inst);
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void setProbeDistributionFactor(Instruction &Inst, float Factor);
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bool moveAndDanglePseudoProbes(BasicBlock *From, Instruction *To);
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bool removeRedundantPseudoProbes(BasicBlock *Block);
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} // end namespace llvm
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#endif // LLVM_IR_PSEUDOPROBE_H
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