mirror of
https://github.com/tinygo-org/tinygo.git
synced 2026-07-26 14:48:40 +00:00
Ayke van Laethem
b203314c2f
Writing the pointer of a buffer to memory-mapped I/O will normally cause it to escape, which forces the compiler to heap-allocate the buffer. But we do know how long the value stays alive, so we can tell the compiler to keep it alive exactly until it is not needed anymore - and tell it to not treat the pointer-to-uintptr cast as escaping.
124 lines
2.8 KiB
Go
124 lines
2.8 KiB
Go
package main
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import (
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"runtime/volatile"
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"unsafe"
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)
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func main() {
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n1 := 5
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derefInt(&n1)
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// This should eventually be modified to not escape.
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n2 := 6 // OUT: object allocated on the heap: escapes at line 14
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returnIntPtr(&n2)
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s1 := make([]int, 3)
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readIntSlice(s1)
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s2 := [3]int{}
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readIntSlice(s2[:])
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// This should also be modified to not escape.
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s3 := make([]int, 3) // OUT: object allocated on the heap: escapes at line 24
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returnIntSlice(s3)
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useSlice(make([]int, getUnknownNumber())) // OUT: object allocated on the heap: size is not constant
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s4 := make([]byte, 300) // OUT: object allocated on the heap: object size 300 exceeds maximum stack allocation size 256
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readByteSlice(s4)
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s5 := make([]int, 4) // OUT: object allocated on the heap: escapes at line 32
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_ = append(s5, 5)
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s6 := make([]int, 3)
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s7 := []int{1, 2, 3}
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copySlice(s6, s7)
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c1 := getComplex128() // OUT: object allocated on the heap: escapes at line 39
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useInterface(c1)
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n3 := 5
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func() int {
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return n3
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}()
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callVariadic(3, 5, 8) // OUT: object allocated on the heap: escapes at line 46
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s8 := []int{3, 5, 8} // OUT: object allocated on the heap: escapes at line 49
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callVariadic(s8...)
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n4 := 3 // OUT: object allocated on the heap: escapes at line 53
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n5 := 7 // OUT: object allocated on the heap: escapes at line 53
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func() {
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n4 = n5
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}()
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println(n4, n5)
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// This shouldn't escape.
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var buf [32]byte
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s := string(buf[:])
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println(len(s))
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var rbuf [5]rune
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s = string(rbuf[:])
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println(s)
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// Unsafe usage of DMA buffers: the compiler thinks this buffer won't be
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// used anymore after the volatile store.
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var dmaBuf1 [4]byte
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pseudoVolatile.Set(uint32(unsafeNoEscape(unsafe.Pointer(&dmaBuf1[0]))))
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// Safe usage of DMA buffers: keep the buffer alive until it is no longer
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// needed, but don't mark it as needing to be heap allocated. The compiler
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// will keep the buffer stack allocated if possible.
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var dmaBuf2 [4]byte
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pseudoVolatile.Set(uint32(unsafeNoEscape(unsafe.Pointer(&dmaBuf2[0]))))
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// ...use the buffer in the DMA peripheral
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keepAliveNoEscape(unsafe.Pointer(&dmaBuf2[0]))
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}
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func derefInt(x *int) int {
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return *x
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}
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func returnIntPtr(x *int) *int {
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return x
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}
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func readIntSlice(s []int) int {
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return s[1]
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}
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func readByteSlice(s []byte) byte {
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return s[1]
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}
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func returnIntSlice(s []int) []int {
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return s
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}
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func getUnknownNumber() int
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func copySlice(out, in []int) {
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copy(out, in)
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}
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func getComplex128() complex128
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func useInterface(interface{})
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func callVariadic(...int)
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func useSlice([]int)
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// See the function with the same name in the machine package.
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//
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//go:linkname unsafeNoEscape machine.unsafeNoEscape
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func unsafeNoEscape(ptr unsafe.Pointer) uintptr
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//go:linkname keepAliveNoEscape machine.keepAliveNoEscape
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func keepAliveNoEscape(ptr unsafe.Pointer)
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var pseudoVolatile volatile.Register32
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