ebe09e2a95
This change improves FS discriminators in the following ways: (1) use call-stack debug information in the the to generate discriminators: the same (src/line) DILs can now have same discriminator value if they come from different call-stacks. This effectively increases the usable discriminator values for each round of FS discriminator pass. (2) don't generate the FS discriminator for meta instructions (i.e. instructions not emitted). This reduces the number discriminators conflicts (for the case we run out of discriminator bits for that pass). (3) use less expensive hashing of xxHash64. These improvements should bring better performance for FSAFDO and they should be used by default. But this change creates incompatible FS discriminators. For the iterative profile users, they might see a performance drop in the first release with this change (due to the fact that the profiles have the old discriminators and the compiler uses the new discriminator). We have measured that this is not more than 1.5% on several benchmarks. Note the degradation should be gone in the second release and one should expect a performance gain over the binary without this change. One possible solution to the iterative profile issue would be separating discriminators for profile-use and the ones emitted to the binary. This would require a mechanism to allow two sets of discriminators to be maintained and then phasing out the first approach. This is too much churn in the compiler and the performance implications do not seem to be worth the effort. Instead, we put the changes under an option so iterative profile users can do a gradual rollout of this change. We will make the option default value to true in a later patch and eventually purge this option from the code base. Differential Revision: https://reviews.llvm.org/D145171
50 lines
2.1 KiB
C++
50 lines
2.1 KiB
C++
//===- llvm/CodeGen/PseudoProbePrinter.cpp - Pseudo Probe Emission -------===//
|
|
//
|
|
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
|
|
// See https://llvm.org/LICENSE.txt for license information.
|
|
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This file contains support for writing pseudo probe info into asm files.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "PseudoProbePrinter.h"
|
|
#include "llvm/CodeGen/AsmPrinter.h"
|
|
#include "llvm/IR/DebugInfoMetadata.h"
|
|
#include "llvm/IR/Function.h"
|
|
#include "llvm/IR/PseudoProbe.h"
|
|
#include "llvm/MC/MCPseudoProbe.h"
|
|
#include "llvm/MC/MCStreamer.h"
|
|
|
|
using namespace llvm;
|
|
|
|
PseudoProbeHandler::~PseudoProbeHandler() = default;
|
|
|
|
void PseudoProbeHandler::emitPseudoProbe(uint64_t Guid, uint64_t Index,
|
|
uint64_t Type, uint64_t Attr,
|
|
const DILocation *DebugLoc) {
|
|
// Gather all the inlined-at nodes.
|
|
// When it's done ReversedInlineStack looks like ([66, B], [88, A])
|
|
// which means, Function A inlines function B at calliste with a probe id 88,
|
|
// and B inlines C at probe 66 where C is represented by Guid.
|
|
SmallVector<InlineSite, 8> ReversedInlineStack;
|
|
auto *InlinedAt = DebugLoc ? DebugLoc->getInlinedAt() : nullptr;
|
|
while (InlinedAt) {
|
|
auto Name = InlinedAt->getSubprogramLinkageName();
|
|
// Use caching to avoid redundant md5 computation for build speed.
|
|
uint64_t &CallerGuid = NameGuidMap[Name];
|
|
if (!CallerGuid)
|
|
CallerGuid = Function::getGUID(Name);
|
|
uint64_t CallerProbeId = PseudoProbeDwarfDiscriminator::extractProbeIndex(
|
|
InlinedAt->getDiscriminator());
|
|
ReversedInlineStack.emplace_back(CallerGuid, CallerProbeId);
|
|
InlinedAt = InlinedAt->getInlinedAt();
|
|
}
|
|
|
|
SmallVector<InlineSite, 8> InlineStack(llvm::reverse(ReversedInlineStack));
|
|
Asm->OutStreamer->emitPseudoProbe(Guid, Index, Type, Attr, InlineStack,
|
|
Asm->CurrentFnSym);
|
|
}
|