<pre>
const (
	c1 = imag(2i)                    // imag(2i) = 2.0 is a constant
	c2 = len([10]float64{2})         // [10]float64{2} contains no function calls
	c3 = len([10]float64{c1})        // [10]float64{c1} contains no function calls
	c4 = len([10]float64{imag(2i)})  // imag(2i) is a constant and no function call is issued
	c5 = len([10]float64{imag(z)})   // invalid: imag(z) is a (non-constant) function call
)
var z complex128
</pre>

pkg go/constant, func Float32Val(Value) (float32, bool)
pkg go/constant, func Float64Val(Value) (float64, bool)
pkg go/constant, func Imag(Value) Value
pkg go/constant, func Int64Val(Value) (int64, bool)
pkg go/constant, func MakeBool(bool) Value
pkg go/constant, func MakeFloat64(float64) Value
pkg go/constant, func MakeFromBytes([]uint8) Value
pkg go/constant, func MakeFromLiteral(string, token.Token, uint) Value

To install:

1) chrome://extensions/
2) click "[+] Developer Mode" in top right
3) "Load unpacked extension..."
4) pick $GOROOT/misc/chrome/gophertool

//
// floating point conditional branch
//
//	LBRA rel
label4:
	BFPT	1(PC)	// BFPT 1(PC)			// 4501000100000000
	BFPT	label4	// BFPT 24			// 4501fffd00000000

//inst:
//
// load ints and bytes
//
//	LMOVV rreg ',' rreg
//	{
//		outcode(int($1), &$2, 0, &$4);
//	}
	MOVV	R25, R17	// 00198825
	MOVV	R1, R2		// 00011025
	MOVV	LO, R1		// 00000812
	MOVV	HI, R1		// 00000810

	LAX	R7, R8, (R9)          // eb87900000f7
	LAXG	R10, R11, (R12)       // ebbac00000e7
	LAO	R1, R2, (R3)          // eb21300000f6
	LAOG	R4, R5, (R6)          // eb54600000e6

	// load and store multiple
	LMG	n-8(SP), R3, R4         // eb34f0100004
	LMG	-5(R5), R3, R4          // eb345ffbff04
	LMY	n-8(SP), R3, R4         // 9834f010
	LMY	4096(R1), R3, R4        // eb3410000198

Example

As a simple example, consider a package that uses cgo to call C.sin.
The following code will be generated by cgo:

	// compiled by gc

	//go:cgo_ldflag "-lm"

	type _Ctype_double float64

	//go:cgo_import_static _cgo_gcc_Cfunc_sin
	//go:linkname __cgo_gcc_Cfunc_sin _cgo_gcc_Cfunc_sin
	var __cgo_gcc_Cfunc_sin byte
	var _cgo_gcc_Cfunc_sin = unsafe.Pointer(&__cgo_gcc_Cfunc_sin)

pkg syscall (windows-amd64), type SysProcAttr struct, ThreadAttributes *SecurityAttributes
pkg testing, func Init()
pkg testing, method (*B) ReportMetric(float64, string)
pkg testing, type BenchmarkResult struct, Extra map[string]float64
pkg text/template, method (ExecError) Unwrap() error
pkg time, method (Duration) Microseconds() int64
pkg time, method (Duration) Milliseconds() int64

	c.uint8 = c.Ident("uint8")
	c.uint16 = c.Ident("uint16")
	c.uint32 = c.Ident("uint32")
	c.uint64 = c.Ident("uint64")
	c.uintptr = c.Ident("uintptr")
	c.float32 = c.Ident("float32")
	c.float64 = c.Ident("float64")
	c.complex64 = c.Ident("complex64")
	c.complex128 = c.Ident("complex128")
	c.void = c.Ident("void")
	c.string = c.Ident("string")
	c.goVoid = c.Ident("_Ctype_void")

	MOV	$0, 0(SP)			// ERROR "constant load must target register"
	MOV	$0, 8(SP)			// ERROR "constant load must target register"
	MOV	$1234, 0(SP)			// ERROR "constant load must target register"
	MOV	$1234, 8(SP)			// ERROR "constant load must target register"
	MOVB	$1, X5				// ERROR "unsupported constant load"
	MOVH	$1, X5				// ERROR "unsupported constant load"
	MOVW	$1, X5				// ERROR "unsupported constant load"

pkg math, func Jn(int, float64) float64
pkg math, func Ldexp(float64, int) float64
pkg math, func Lgamma(float64) (float64, int)
pkg math, func Log(float64) float64
pkg math, func Log10(float64) float64
pkg math, func Log1p(float64) float64
pkg math, func Log2(float64) float64
pkg math, func Logb(float64) float64
pkg math, func Max(float64, float64) float64
pkg math, func Min(float64, float64) float64