google/benchmark

benchmark::MakeUnpredictable

Open

#341 opened on Feb 11, 2017

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 (13 comments) (0 reactions) (1 assignee)C++ (7,968 stars) (1,539 forks)batch import
enhancementhelp wantedincomplete

Description

folly::benchmark includes makeUnpredictable function to hide a compile-time constant value of a variable from optimizer. This is a very useful feature, and google::benchmark should provide something similar.

Contributor guide

Tech stack
cpp
Domain
performance
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
blocked
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C++compiler optimizationbenchmarking
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
Study the existing DoNotOptimize function in include/benchmark/benchmark.h and its implementation. Review folly's MakeUnpredictable implementation to understand the compiler barrier technique. Look at the issue comments for any additional context or proposed approaches. Consider using compiler built ins or inline assembly to achieve the same effect in google benchmark.
benchmark::MakeUnpredictable · google/benchmark#341 | Good First Issue