[PATCH v1 0/7] DCE/DSE: Add Dead Syscalls Elimination support, part1

[Yuan Tan]

Here is a test result about DEAD_CODE_DATA_ELIMINATION (DCE) and dead syscalls
elimination (DSE). It's based on config[1] and a simple hello.c initramfs.

In the DSE test, we set CONFIG_SYSCALLS_USED="sys_write sys_exit sys_reboot,"
which is used by hello.c to simply print "Hello" then exit and shut down qemu.

|                                    | syscall remain | vmlinux size     | vmlinux after trip |
| ---------------------------------- | -------------- | ---------------- | ------------------ |
| disable DCE                        | 236            | 2559632          | 1963400            |
| enable DCE                         | 208            | 2037384 (-20.4%) | 1485776 (-24.3%)   |
| enable DCE and DSE(SHE_GROUP)      | 3              | 1856640 (-27.6%) | 1354424 (-31.0%)   |
| enable DCE and DSE(SHE_LINK_ORDER) | 3              | 1856664 (-27.6%) | 1354424 (-31.0%)   |

It shows that dead syscalls elimination can save 7% of space based on DCE.

[1]: https://pastebin.com/KG4fd7aT