[llvm] Disable linking llvm-exegesis to dylib

[mgorny]

Summary

Force linking llvm-exegesis to static LLVM libraries instead of dylib
to prevent duplicate symbols due to linking both. Ideally, we'd want
to link to the dylib only here but the target sub-libraries use hidden
symbols from LLVM target libraries and therefore linking the dylib
fails.

[MaskRay]

Can you please add some messages about duplicate symbols?

[mgorny]

In D81922#2095834, @MaskRay wrote:

Can you please add some messages about duplicate symbols?

I don't understand what you mean. If you're asking for something that actually fails due to linking both copies of the library, I haven't seen one with llvm-exegesis. I did have problems with clangd, so I'm trying to correct linkage everywhere.

[aaronpuchert]

In D81922#2095834, @MaskRay wrote:

Can you please add some messages about duplicate symbols?

When linking with libpfm (set -DLLVM_ENABLE_LIBPFM=ON when configuring), I get an error without this change:

> llvm-exegesis --help
: CommandLine Error: Option 'x86-use-base-pointer' registered more than once!
LLVM ERROR: inconsistency in registered CommandLine options
Aborted (core dumped)

When not linking with libpfm, I can't reliably reproduce it. The functionality of llvm-exegesis is reduced then, and it probably doesn't use any target internals, or at least not enough to cause a problem.

llvm/tools/llvm-exegesis/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS
   MCParser
   Support
   native
   )
 
 add_llvm_tool(llvm-exegesis
+  DISABLE_LLVM_LINK_LLVM_DYLIB
   llvm-exegesis.cpp
   )
 
 add_subdirectory(lib)
 
 # Link the native exegesis target if compiled and on the right host.
 if ((LLVM_TARGETS_TO_BUILD MATCHES "${LLVM_NATIVE_ARCH}") AND (LLVM_EXEGESIS_TARGETS MATCHES "${LLVM_NATIVE_ARCH}"))
   set(LLVM_EXEGESIS_NATIVE_ARCH "${LLVM_NATIVE_ARCH}")