internal/buildcfg: enable greenteagc experiment by default

Slightly bump the value in Test/wasmmemsize.go. We use 1 additional page
compared to before, and we were already sitting *right* on the edge.

For golang#73581.

Change-Id: I485df16c3cf59803a8a1fc852b3e90666981ab09
Reviewed-on: https://go-review.googlesource.com/c/go/+/656195
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Michael Knyszek <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: mknyszek

src/internal/buildcfg/exp.go

@@ -78,12 +78,18 @@ func ParseGOEXPERIMENT(goos, goarch, goexp string) (*ExperimentFlags, error) {
 	// things like .debug_addr (needed for DWARF 5).
 	dwarf5Supported := (goos != "darwin" && goos != "ios" && goos != "aix")
 
+	// The compiler crashes while compiling some of the Green Tea code.
+	// The Green Tea code is pretty normal, so this is likely a compiler
+	// bug in the loong64 port.
+	greenTeaGCSupported := goarch != "loong64"
+
 	baseline := goexperiment.Flags{
 		RegabiWrappers:        regabiSupported,
 		RegabiArgs:            regabiSupported,
 		Dwarf5:                dwarf5Supported,
 		RandomizedHeapBase64:  true,
 		SizeSpecializedMalloc: true,
+		GreenTeaGC:            greenTeaGCSupported,
 	}
 
 	// Start with the statically enabled set of experiments.

test/wasmmemsize.dir/main.go

@@ -9,17 +9,19 @@ import (
 	"io"
 )
 
-// Expect less than 3 MB of memory usage for a small wasm program.
-// This reflects the current allocator. If the allocator changes,
-// update this value.
-const want = 3 << 20
+// Wasm page size.
+const pageSize = 64 * 1024
+
+// Expect less than 3 MB + 1 page of memory usage for a small wasm
+// program. This reflects the current allocator. If the allocator
+// changes, update this value.
+const want = 3<<20 + pageSize
 
 var w = io.Discard
 
 func main() {
 	fmt.Fprintln(w, "hello world")
 
-	const pageSize = 64 * 1024
 	sz := uintptr(currentMemory()) * pageSize
 	if sz > want {
 		fmt.Printf("FAIL: unexpected memory size %d, want <= %d\n", sz, want)