Description
| Previous ID | SR-521 |
| Radar | None |
| Original Reporter | @allevato |
| Type | Bug |
| Status | Resolved |
| Resolution | Done |
Environment
Tested on OS X:
Swift version 2.2-dev (LLVM 46be9ff861, Clang 4deb154edc, Swift 51a9cea5cd)
Target: x86_64-apple-macosx10.9
Tested on Linux:
Swift version 2.2-dev (LLVM 3ebdbb2c7e, Clang f66c5bb67b, Swift 1f2908b4f7)
Target: x86_64-unknown-linux-gnu
Additional Detail from JIRA
| Votes | 0 |
| Component/s | Compiler, Package Manager |
| Labels | Bug |
| Assignee | None |
| Priority | Medium |
md5: 58e0a16182b3604b18df177057c9bc29
relates to:
- SR-1021 Don't export public symbols from static libraries by default
Issue Description:
Symbols declared with public visibility are never dead stripped by the linker, even when linking an executable where there is no expectation that the result would be linked into anything else (and thus unused symbols could be safely discarded).
Stripping these symbols is important when building an executable that links to a large library that it only uses a portion of, to prevent code bloat.
STEPS TO REPRODUCE
1. Create functions.swift, first using internal visibility:
func foo() { print("foo") }
func bar() { print("bar") }2. Create main.swift:
bar()3. Build an executable (example provided is for OS X):
swiftc functions.swift main.swift -Xlinker -dead_strip
4. Run nm main and observe that foo has been stripped from the executable.
5. Modify functions.swift to declare the functions with public visibility:
public func foo() { print("foo") }
public func bar() { print("bar") }6. Build the executable again:
swiftc functions.swift main.swift -Xlinker -dead_strip
7. Run nm main and observe that foo is still present.
EXPECTED BEHAVIOR
foo should be removed because we are building an executable and it is never referenced within that binary.
OTHER NOTES
On OS X, adding the -whole-module-optimization option to swiftc has no effect.
On Linux, the behavior differs. -Xlinker -dead_strip doesn't apply here; instead, we see the following based on -whole-module-optimization:
1. Internal visibility compiled without -whole-module-optimization: foo is not stripped
2. Internal visibility compiled with -whole-module-optimization: foo is stripped
3. Public visibility regardless of the presence of -whole-module-optimization: foo is not stripped