“芝麻”大的权利，也不能拱手相让

There is no inherent performance difference between using continue and if-else in loops; both compile to similar machine code with modern optimizations. 2. The choice should be based on readability: use continue for early exits in multi-condition checks to reduce nesting, and if-else for simple logic. 3. Performance impacts arise from poor logic ordering, such as performing expensive operations before a skip decision, not from the control flow keyword itself. 4. In both compiled and interpreted languages, compilers and interpreters optimize jumps similarly, making the performance impact negligible when logic is equivalent. 5. The real bottleneck comes from doing unnecessary work before skipping, unpredictable branches, or unoptimized calls, so focus on structuring the hot path efficiently rather than micro-optimizing keywords, as the compiler typically handles control flow optimization effectively.

When writing loops in performance-critical code, developers often wonder whether using continue to skip iterations is more efficient than wrapping logic in an if-else block. While both approaches can achieve similar control flow, their performance can differ based on context, compiler optimizations, and the structure of the loop body. Let’s break down the practical differences between continue and if-else in loops and examine when one might outperform the other.

1. Control Flow and Readability

At the code level, continue allows you to skip the rest of the current iteration and proceed to the next one. This is useful when you want to filter out certain cases early:

# Using continue
for item in data:
    if not condition(item):
        continue
    # Process item
    process(item)

Alternatively, you can use an if block:

# Using if-else
for item in data:
    if condition(item):
        process(item)

Both are functionally equivalent in this case, but the if version is often more readable because it avoids an extra control jump. The continue version can become clearer when you have multiple early-exit conditions:

for item in data:
    if not condition1(item):
        continue
    if not condition2(item):
        continue
    if not condition3(item):
        continue
    process(item)

This style reduces nesting and can improve maintainability.

2. Performance: Does continue Introduce Overhead?

In most modern compilers and interpreters, there is no measurable performance difference between continue and if-guarded logic when the logic is equivalent. Here's why:

• The continue statement compiles down to a conditional jump instruction in machine code.
• An if block also compiles to a conditional jump.
• In both cases, the CPU’s branch predictor handles the jump similarly.

For example, in C:

// Version A: continue
for (int i = 0; i < n; i  ) {
    if (arr[i] < 0) continue;
    sum  = arr[i];
}

// Version B: if
for (int i = 0; i < n; i  ) {
    if (arr[i] >= 0) {
        sum  = arr[i];
    }
}

With optimization enabled (e.g., -O2), both typically produce nearly identical assembly. The compiler may even restructure the code to minimize jumps.

3. When Structure Affects Performance

Performance differences arise not from continue vs if, but from how much code is skipped and where the hot path lies.

Consider this scenario:

for item in data:
    if slow_precondition_check(item):
        continue
    expensive_operation(item)

vs.

for item in data:
    if not slow_precondition_check(item):
        expensive_operation(item)

Here, the performance is identical — the expensive call only happens when the condition fails. But if you reverse the logic and place the expensive operation outside a continue, you might accidentally execute setup code before skipping.

A more subtle issue: placing continue after several expensive operations defeats its purpose:

for item in data:
    result = heavy_computation(item)
    if not meets_criteria(result):
        continue  # Too late — work already done
    finalize(result)

This is inefficient regardless of continue usage — the problem is logic ordering, not the keyword.

4. Compiler and Interpreter Optimizations

In compiled languages like C, Rust, or Go, the compiler often eliminates unnecessary jumps and flattens control flow. So whether you write continue or wrap the body in an if, the generated code may be identical.

In interpreted languages like Python, each bytecode instruction has a cost. Let’s look at a simple benchmark:

# Test data
data = [i for i in range(1000000)]

# Version 1: continue
def with_continue():
    total = 0
    for x in data:
        if x % 2 == 1:
            continue
        total  = x
    return total

# Version 2: if
def with_if():
    total = 0
    for x in data:
        if x % 2 == 0:
            total  = x
    return total

Running both with timeit, the results are typically within noise. Any difference is due to bytecode order, not fundamental efficiency.

Bottom Line

• No inherent performance advantage of continue over if or vice versa.
• Code clarity should guide your choice:
  • Use continue for early filtering in multi-condition loops.
  • Use if when the logic is simple and nested structure is acceptable.
• Performance bottlenecks usually come from:
  • Doing work before deciding to skip.
  • Poor branch prediction (e.g., random conditions).
  • Unoptimized function calls inside the loop.

So, focus on structuring your loop to minimize unnecessary computation rather than micro-optimizing control flow keywords. The compiler has your back on the rest.

Basically, it’s not continue vs if-else — it’s about writing the hot path clearly and avoiding work you don’t need to do.

The above is the detailed content of Dissecting Loop Efficiency: A Performance Benchmark of `continue` vs. `if-else`. For more information, please follow other related articles on the PHP Chinese website!