Benchmark: branch prediction

Tests:

with 0 check
let idx = 0; while (idx < 1000000) { if (idx != 0) { } idx++; }
without 0 check
let idx = 0; while (idx < 1000000) { idx++; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
with 0 check
without 0 check

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 3 months ago)

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/144.0.0.0 Safari/537.36

Browser/OS: Chrome 144 on Linux

View result in a separate tab

Test name	Executions per second
with 0 check	3988.2 Ops/sec
without 0 check	4002.5 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks on MeasureThat.net.

**What is tested?**

The provided benchmark tests the branch prediction behavior of modern web browsers, specifically Mozilla Firefox. Branch prediction is the ability of the CPU to guess which branch (i.e., code path) a program will take based on historical data. This can significantly impact performance and power consumption.

In this benchmark, two test cases are compared:

1. **"with 0 check"**: This test case has an if-statement that checks if `idx` is not equal to 0 before executing some code. If the condition is true, no code is executed.
2. **"without 0 check"**: This test case has a similar loop structure without the if-statement.

**Options compared**

The benchmark compares two approaches:

1. **With explicit branch prediction (if-statement)**: In this approach, the browser's CPU needs to decide whether to execute the code inside the if-statement or not.
2. **Without explicit branch prediction (no if-statement)**: In this case, the browser's CPU can infer that the loop will always increment `idx` and therefore predict a certain branch.

**Pros and cons of each approach**

* **With explicit branch prediction (if-statement)**:
	+ Pros: Can help the CPU make more accurate predictions about branch behavior.
	+ Cons: May lead to slightly slower performance due to the overhead of the if-statement.
* **Without explicit branch prediction (no if-statement)**:
	+ Pros: Reduces branch prediction overhead, potentially leading to faster performance.
	+ Cons: Can lead to incorrect branch predictions, affecting overall performance.

**Library and its purpose**

In this benchmark, there is no external library used. The test cases only rely on standard JavaScript features.

**Special JS feature or syntax**

There are no special JavaScript features or syntax mentioned in the benchmark definition or individual test cases.

**Other alternatives**

For measuring branch prediction behavior, you can consider other microbenchmarks that specifically target this aspect of performance. Some examples include:

* **Branch Misprediction Benchmark**: Tests how often a CPU mispredicts branches.
* **Loop Unrolling Benchmark**: Measures the performance impact of loop unrolling on modern CPUs.

**Benchmark preparation code**

The provided benchmark preparation code is minimal, with only a few lines of JavaScript code defining each test case. The scripts use standard JavaScript features and syntax to create loops that exercise branch prediction behavior in the browser's CPU.

Here's an example of how you might write a similar benchmark using standard JavaScript:
```javascript
const numLoops = 1000000;
for (let i = 0; i < numLoops; i++) {
  if (i !== 0) { // with explicit branch prediction
    // do nothing
  } else {
    // do something
  }
}
```
Note that this is a simplified example and may not exactly replicate the behavior of the MeasureThat.net benchmark.

Related benchmarks:

branch prediction (version: 0)

Comparing performance of: with 0 check vs without 0 check

Created: 4 years ago by: Registered User

Jump to the latest result

with 0 check

without 0 check

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):