mirror of
https://github.com/intel/llvm.git
synced 2026-01-14 03:50:17 +08:00
d0e98909d2
Add the flag `--tail-merge-strings` to enable tail merging of cstrings.
For example, if we have strings `mystring\0` and `ring\0`, we could
place `mystring\0` at address `0x1000` and `ring\0` at address `0x1004`
and have them share the same underlying data.
It turns out that many ObjC method names can be tail merged. For
example, `error:` and `doFoo:error:`. On a large iOS binary, we saw
nearly a 15% size improvement in the `__TEXT__objc_methname` section and
negligible impact on link time.
```
$ bloaty --domain=vm merged.o.stripped -- base.o.stripped
VM SIZE
--------------
+95% +5.85Ki [__TEXT]
-2.4% -239Ki __TEXT,__cstring
-14.5% -710Ki __TEXT,__objc_methname
-1.0% -944Ki TOTAL
```
Tail merging for MachO was originally removed in
7c269db779.
The previous implementation used `StringTableBuilder`, but that was
removed in
4308f031cd
to ensure deduplicated strings are aligned correctly. This
implementation ensures that tail merged strings are also aligned
correctly.
Special thanks to nocchijiang for pointing this out in
https://github.com/llvm/llvm-project/pull/158720#issuecomment-3310416030.
Depends on https://github.com/llvm/llvm-project/pull/161253.
lld Documentation ================= The lld documentation is written using the Sphinx documentation generator. It is currently tested with Sphinx 1.1.3. We currently use the 'nature' theme and a Beaker inspired structure. See sphinx_intro.rst for more details.