How Does Mixing `Println` and `Fmt.Println` Impact Stack Growth in Go?

Mixing Println and Fmt.Println Effects on Stack Growth

In Go, the allocation and growth of the stack depend on the usage of functions like println() and fmt.Println().

Println() vs. Fmt.Println()

Println() is a builtin function known to the compiler, which implies that its arguments will not escape to the heap. In contrast, fmt.Println(), belonging to the standard library, is treated like any user-defined function. The compiler cannot guarantee that its arguments will not escape, so these arguments are allocated on the heap rather than the stack.

Impact on Stack Growth

When the stack runs out of space, a larger stack is allocated. Consequently, stack-allocated variables are moved, changing their addresses. This movement occurs because the recursive function stackCopy() is passed a significant argument (an array of size 1024). The initial stack allocated is insufficient, necessitating a larger stack and the relocation of variables.

When fmt.Println() is used, the compiler recognizes that the argument s may escape and allocates it on the heap. As a result, stack growth does not trigger s's movement.

Escape Analysis

To understand this behavior further, one can leverage the "-gcflags '-m'" flags during compilation, which disclose the compiler's escape analysis. In the case of using only println(), the analysis reveals that s does not escape. Conversely, when mixing println() and fmt.Println(), the compiler infers that s escapes and allocates it on the heap.

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