Auto merge of #118636 - h1467792822:dev, r=michaelwoerister

Add the unstable option  to reduce the binary size of dynamic library…

# Motivation

The average length of symbol names in the rust standard library is about 100 bytes, while the average length of symbol names in the C++ standard library is about 65 bytes. In some embedded environments where dynamic library are widely used, rust dynamic library symbol name space hash become one of the key bottlenecks of application, Especially when the existing C/C++ module is reconstructed into the rust module.

The unstable option `-Z symbol_mangling_version=hashed` is added to solve the bottleneck caused by too long dynamic library symbol names.

## Test data

The following is a set of test data on the ubuntu 18.04 LTS environment. With this plug-in, the space saving rate of dynamic libraries can reach about 20%.

The test object is the standard library of rust (built based on Xargo), tokio crate, and hyper crate.

The contents of the Cargo.toml file in the construction project of the three dynamic libraries are as follows:

```txt
# Cargo.toml
[profile.release]
panic = "abort"
opt-leve="z"
codegen-units=1
strip=true
debug=true
```
The built dynamic library also removes the `.rustc` segments that are not needed at run time and then compares the size. The detailed data is as follows:

1. libstd.so
> | symbol_mangling_version | size | saving rate |
> | --- | --- | --- |
> | legacy | 804896 ||
> | hashed | 608288 | 0.244 |
> | v0 | 858144 ||
> | hashed | 608288 | 0.291 |

2. libhyper.so
> | symbol_mangling_version(libhyper.so) | symbol_mangling_version(libstd.so) | size | saving rate |
> | --- | --- | --- | --- |
> | legacy | legacy | 866312 ||
> | hashed | legacy | 645128 |0.255|
> | legacy | hashed | 854024 ||
> | hashed | hashed | 632840 |0.259|

10 files changed, 84 insertions, 4 deletions

diff --git a/tests/run-make/symbol-mangling-hashed/Makefile b/tests/run-make/symbol-mangling-hashed/Makefile
new file mode 100644
index 00000000000..68894b2192a
--- /dev/null
+++ b/tests/run-make/symbol-mangling-hashed/Makefile
@@ -0,0 +1,48 @@
+include ../tools.mk
+
+# ignore-cross-compile
+# only-linux
+# only-x86_64
+
+NM=nm -D
+RLIB_NAME=liba_rlib.rlib
+DYLIB_NAME=liba_dylib.so
+SO_NAME=libb_dylib.so
+BIN_NAME=b_bin
+
+ifeq ($(UNAME),Darwin)
+NM=nm -gU
+RLIB_NAME=liba_rlib.rlib
+DYLIB_NAME=liba_dylib.dylib
+SO_NAME=libb_dylib.dylib
+BIN_NAME=b_bin
+endif
+
+ifdef IS_WINDOWS
+NM=nm -g
+RLIB_NAME=liba_rlib.dll.a
+DYLIB_NAME=liba_dylib.dll
+SO_NAME=libb_dylib.dll
+BIN_NAME=b_bin.exe
+endif
+
+all:
+	$(RUSTC) -C prefer-dynamic -Z unstable-options -C symbol-mangling-version=hashed -C metadata=foo a_dylib.rs
+	$(RUSTC) -C prefer-dynamic -Z unstable-options -C symbol-mangling-version=hashed -C metadata=bar a_rlib.rs
+	$(RUSTC) -C prefer-dynamic -L $(TMPDIR) b_dylib.rs
+	$(RUSTC) -C prefer-dynamic -L $(TMPDIR) b_bin.rs
+
+    # Check hashed symbol name
+
+	[ "$$($(NM) $(TMPDIR)/$(DYLIB_NAME) | grep -c hello)" -eq "0" ]
+	[ "$$($(NM) $(TMPDIR)/$(DYLIB_NAME) | grep _RNxC7a_dylib | grep -c ' T ')" -eq "1" ]
+
+	[ "$$($(NM) $(TMPDIR)/$(SO_NAME) | grep b_dylib | grep -c hello)" -eq "1" ]
+	[ "$$($(NM) $(TMPDIR)/$(SO_NAME) | grep _RNxC6a_rlib | grep -c ' T ')" -eq "1" ]
+	[ "$$($(NM) $(TMPDIR)/$(SO_NAME) | grep _RNxC7a_dylib | grep -c ' U ')" -eq "1" ]
+
+	[ "$$($(NM) $(TMPDIR)/$(BIN_NAME) | grep _RNxC6a_rlib | grep -c ' U ')" -eq "1" ]
+	[ "$$($(NM) $(TMPDIR)/$(BIN_NAME) | grep _RNxC7a_dylib | grep -c ' U ')" -eq "1" ]
+	[ "$$($(NM) $(TMPDIR)/$(BIN_NAME) | grep b_dylib | grep hello | grep -c ' U ')" -eq "1" ]
+
+	$(call RUN,$(BIN_NAME))
diff --git a/tests/run-make/symbol-mangling-hashed/a_dylib.rs b/tests/run-make/symbol-mangling-hashed/a_dylib.rs
new file mode 100644
index 00000000000..8aec8fd82a5
--- /dev/null
+++ b/tests/run-make/symbol-mangling-hashed/a_dylib.rs
@@ -0,0 +1,4 @@
+#![crate_type="dylib"]
+pub fn hello() {
+    println!("hello dylib");
+}
diff --git a/tests/run-make/symbol-mangling-hashed/a_rlib.rs b/tests/run-make/symbol-mangling-hashed/a_rlib.rs
new file mode 100644
index 00000000000..873c86c5d0b
--- /dev/null
+++ b/tests/run-make/symbol-mangling-hashed/a_rlib.rs
@@ -0,0 +1,5 @@
+#![crate_type="rlib"]
+
+pub fn hello() {
+    println!("hello rlib");
+}
diff --git a/tests/run-make/symbol-mangling-hashed/b_bin.rs b/tests/run-make/symbol-mangling-hashed/b_bin.rs
new file mode 100644
index 00000000000..bcc53c37e12
--- /dev/null
+++ b/tests/run-make/symbol-mangling-hashed/b_bin.rs
@@ -0,0 +1,9 @@
+extern crate a_rlib;
+extern crate a_dylib;
+extern crate b_dylib;
+
+fn main() {
+    a_rlib::hello();
+    a_dylib::hello();
+    b_dylib::hello();
+}
diff --git a/tests/run-make/symbol-mangling-hashed/b_dylib.rs b/tests/run-make/symbol-mangling-hashed/b_dylib.rs
new file mode 100644
index 00000000000..c26a04b39ec
--- /dev/null
+++ b/tests/run-make/symbol-mangling-hashed/b_dylib.rs
@@ -0,0 +1,9 @@
+#![crate_type="dylib"]
+
+extern crate a_rlib;
+extern crate a_dylib;
+
+pub fn hello() {
+    a_rlib::hello();
+    a_dylib::hello();
+}
diff --git a/tests/ui/symbol-mangling-version/bad-value.bad.stderr b/tests/ui/symbol-mangling-version/bad-value.bad.stderr
index c36c73c6069..a12e5e241c0 100644
--- a/tests/ui/symbol-mangling-version/bad-value.bad.stderr
+++ b/tests/ui/symbol-mangling-version/bad-value.bad.stderr
@@ -1,2 +1,2 @@
-error: incorrect value `bad-value` for codegen option `symbol-mangling-version` - either `legacy` or `v0` (RFC 2603) was expected
+error: incorrect value `bad-value` for codegen option `symbol-mangling-version` - one of: `legacy`, `v0` (RFC 2603), or `hashed` was expected
 
diff --git a/tests/ui/symbol-mangling-version/bad-value.blank.stderr b/tests/ui/symbol-mangling-version/bad-value.blank.stderr
index 0e70af5b8ff..95456587781 100644
--- a/tests/ui/symbol-mangling-version/bad-value.blank.stderr
+++ b/tests/ui/symbol-mangling-version/bad-value.blank.stderr
@@ -1,2 +1,2 @@
-error: incorrect value `` for codegen option `symbol-mangling-version` - either `legacy` or `v0` (RFC 2603) was expected
+error: incorrect value `` for codegen option `symbol-mangling-version` - one of: `legacy`, `v0` (RFC 2603), or `hashed` was expected
 
diff --git a/tests/ui/symbol-mangling-version/bad-value.no-value.stderr b/tests/ui/symbol-mangling-version/bad-value.no-value.stderr
index 77013b72b6c..325e47a281f 100644
--- a/tests/ui/symbol-mangling-version/bad-value.no-value.stderr
+++ b/tests/ui/symbol-mangling-version/bad-value.no-value.stderr
@@ -1,2 +1,2 @@
-error: codegen option `symbol-mangling-version` requires either `legacy` or `v0` (RFC 2603) (C symbol-mangling-version=<value>)
+error: codegen option `symbol-mangling-version` requires one of: `legacy`, `v0` (RFC 2603), or `hashed` (C symbol-mangling-version=<value>)
 
diff --git a/tests/ui/symbol-mangling-version/unstable.hashed.stderr b/tests/ui/symbol-mangling-version/unstable.hashed.stderr
new file mode 100644
index 00000000000..f2ae18290f2
--- /dev/null
+++ b/tests/ui/symbol-mangling-version/unstable.hashed.stderr
@@ -0,0 +1,2 @@
+error: `-C symbol-mangling-version=hashed` requires `-Z unstable-options`
+
diff --git a/tests/ui/symbol-mangling-version/unstable.rs b/tests/ui/symbol-mangling-version/unstable.rs
index df87a39cdfb..42750a64574 100644
--- a/tests/ui/symbol-mangling-version/unstable.rs
+++ b/tests/ui/symbol-mangling-version/unstable.rs
@@ -1,6 +1,9 @@
-// revisions: legacy legacy-ok
+// revisions: legacy legacy-ok hashed hashed-ok
 // [legacy] compile-flags: -Csymbol-mangling-version=legacy
 // [legacy-ok] check-pass
 // [legacy-ok] compile-flags: -Zunstable-options -Csymbol-mangling-version=legacy
+// [hashed] compile-flags: -Csymbol-mangling-version=hashed
+// [hashed-ok] check-pass
+// [hashed-ok] compile-flags: -Zunstable-options -Csymbol-mangling-version=hashed
 
 fn main() {}