runtime (gc): add a new "list" GC

This memory manager uses a simple linked list to track active allocations, and measures the gaps between them to find available memory.
Performance is not great for large heaps, but is sufficient for microcontrollers with single-digit kilobytes of memory.

Author: niaow

compileopts/options.go

@@ -7,7 +7,7 @@ import (
 )
 
 var (
-	validGCOptions            = []string{"none", "leaking", "extalloc", "conservative"}
+	validGCOptions            = []string{"none", "leaking", "extalloc", "conservative", "list"}
 	validSchedulerOptions     = []string{"none", "tasks", "coroutines"}
 	validSerialOptions        = []string{"none", "uart", "usb"}
 	validPrintSizeOptions     = []string{"none", "short", "full"}

compileopts/options_test.go

@@ -9,7 +9,7 @@ import (
 
 func TestVerifyOptions(t *testing.T) {
 
-	expectedGCError := errors.New(`invalid gc option 'incorrect': valid values are none, leaking, extalloc, conservative`)
+	expectedGCError := errors.New(`invalid gc option 'incorrect': valid values are none, leaking, extalloc, conservative, list`)
 	expectedSchedulerError := errors.New(`invalid scheduler option 'incorrect': valid values are none, tasks, coroutines`)
 	expectedPrintSizeError := errors.New(`invalid size option 'incorrect': valid values are none, short, full`)
 	expectedPanicStrategyError := errors.New(`invalid panic option 'incorrect': valid values are print, trap`)

main.go

@@ -1006,7 +1006,7 @@ func main() {
 	command := os.Args[1]
 
 	opt := flag.String("opt", "z", "optimization level: 0, 1, 2, s, z")
-	gc := flag.String("gc", "", "garbage collector to use (none, leaking, extalloc, conservative)")
+	gc := flag.String("gc", "", "garbage collector to use (none, leaking, extalloc, conservative, list)")
 	panicStrategy := flag.String("panic", "print", "panic strategy (print, trap)")
 	scheduler := flag.String("scheduler", "", "which scheduler to use (none, coroutines, tasks)")
 	serial := flag.String("serial", "", "which serial output to use (none, uart, usb)")

src/runtime/gc_globals_conservative.go

@@ -1,4 +1,4 @@
-// +build gc.conservative gc.extalloc
+// +build gc.conservative gc.extalloc gc.list
 // +build baremetal tinygo.wasm
 
 package runtime

src/runtime/gc_globals_precise.go

@@ -1,4 +1,4 @@
-// +build gc.conservative gc.extalloc
+// +build gc.conservative gc.extalloc gc.list
 // +build !baremetal,!tinygo.wasm
 
 package runtime