The Go compiler

Learn the phases of the Go compiler.

The Go compiler

go build runs the cmd/compile compiler in the background. The phases: parsing (source → syntax tree), type checking, IR generation and escape analysis, inlining, SSA optimizations, and finally machine code. Then cmd/link links the packages into one binary.

go build -x .          # shows the commands it runs
go tool compile -S x.go  # the generated assembly

The Go compiler focuses on fast compilation; even large projects build in seconds.

The build cache

Go caches each package's build result keyed by a hash of its inputs (go env GOCACHE). If no file changed, the package isn't recompiled. go build -a ignores the cache; go clean -cache clears it. For cross-compiling, setting only GOOS and GOARCH is enough.

Exercise Build info

runtime.Version(), runtime.GOOS and runtime.GOARCH tell which toolchain and target the program was built with. Check that runtime.Version() starts with "go" using strings.HasPrefix and print the result.

Show example solution

package main

import (
    "fmt"
    "runtime"
    "strings"
)

func main() {
    fmt.Println(strings.HasPrefix(runtime.Version(), "go"))
}

Test yourself

Which tool combines packages into one binary?
- cmd/compile
- go vet
- gofmt
- cmd/link (the linker)
Show answer

cmd/link (the linker) — The compiler turns each package into an object file; the linker combines them with the runtime into one executable.

See the assembly

go build -gcflags=____ . 2>&1 | head

Show answer

go build -gcflags=-S . 2>&1 | head

Compile phase

Parsing

Syntax tree
Type checking

Type errors
SSA

Optimization
Linking

Single binary

Next lesson: SSA

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