ssa: makeSlice both len/cap be non-nil

internal/runtime/math/math.go

@@ -0,0 +1,15 @@
+package math
+
+import "github.com/goplus/llgo/internal/runtime/goarch"
+
+const MaxUintptr = ^uintptr(0)
+
+// MulUintptr returns a * b and whether the multiplication overflowed.
+// On supported platforms this is an intrinsic lowered by the compiler.
+func MulUintptr(a, b uintptr) (uintptr, bool) {
+	if a|b < 1<<(4*goarch.PtrSize) || a == 0 {
+		return a * b, false
+	}
+	overflow := b > MaxUintptr/a
+	return a * b, overflow
+}