[examples] Skip building the Bye pass plugin on windows

[mstorsjo]

Summary

Windows doesn't properly support pass plugins (as a shared library can't have undefined references, which pass plugins assume, being loaded into a host process that contains provides them), thus disable building it and the corresponding test.

This matches what was done for the passes unit test in bc8e44218810c0db6328b9809c959ceb7d43e3f5.

[amccarth]

Windows doesn't properly support pass plugins (as a shared library can't have undefined references, which pass plugins assume, being loaded into a host process that contains provides them)

This sounds like a problem with the plugin design. Is this patch intended as a temporary workaround until the inherent layering problem is resolved?

[mstorsjo]

In D79771#2031812, @amccarth wrote:

Windows doesn't properly support pass plugins (as a shared library can't have undefined references, which pass plugins assume, being loaded into a host process that contains provides them)

This sounds like a problem with the plugin design. Is this patch intended as a temporary workaround until the inherent layering problem is resolved?

I'm not planning on addressing the general pass plugin design, I just want builds with -DBUILD_SHARED_LIBS=TRUE. The fact that pass plugin can't work on windows is known since https://reviews.llvm.org/D47082 at least, without any plans from others to do anything about it.

[serge-sans-paille]

@mstorsjo Sorry for jumping late on that review, I'd think that the REQUIRES: plugins would be enough, but it turns out LLVM_ENABLE_PLUGINS isset to ON by default on Windows if BUILD_SHARED_LIBS is ON too, which seems to contradict your report. Can you give it a look (I don't have an easy access to a Windows machine)

llvm/examples/Bye/CMakeLists.txt

 if(LLVM_BYE_LINK_INTO_TOOLS)
   message(WARNING "Setting LLVM_BYE_LINK_INTO_TOOLS=ON only makes sense for testing purpose")
 endif()
 
+# The plugin expects to not link against the Support and Core libraries,
+# but expects them to exist in the process loading the plugin. This doesn't
+# work with DLLs on Windows (where a shared library can't have undefined
+# references), so just skip this example on Windows.
+if (NOT WIN32)
   add_llvm_pass_plugin(Bye
     Bye.cpp
     DEPENDS
     intrinsics_gen
     BUILDTREE_ONLY
    )
 
   install(TARGETS ${name} RUNTIME DESTINATION examples)
   set_target_properties(${name} PROPERTIES FOLDER "Examples")
+endif()

llvm/test/CMakeLists.txt

 endif()
 
 if(TARGET LTO)
   set(LLVM_TEST_DEPENDS ${LLVM_TEST_DEPENDS} LTO)
 endif()
 
 if(LLVM_BUILD_EXAMPLES)
   list(APPEND LLVM_TEST_DEPENDS
-    Bye
     Kaleidoscope-Ch3
     Kaleidoscope-Ch4
     Kaleidoscope-Ch5
     Kaleidoscope-Ch6
     Kaleidoscope-Ch7
     )
+  if (NOT WIN32)
+    list(APPEND LLVM_TEST_DEPENDS
+      Bye
+      )
+  endif()
 endif()
 
 if(TARGET ocaml_llvm)
   # Clear all non-OCaml cross-target dependencies when building out-of-tree.
   if(LLVM_OCAML_OUT_OF_TREE)
     set(LLVM_TEST_DEPENDS)
   endif()
 

llvm/test/Feature/load_extension.ll

 ; REQUIRES: x86-registered-target
 ; RUN: opt %s %loadbye -goodbye -wave-goodbye -disable-output 2>&1 | FileCheck %s
 ; RUN: opt %s %loadnewpmbye %loadbye -passes="goodbye" -wave-goodbye -disable-output 2>&1 | FileCheck %s
 ; RUN: opt -module-summary %s -o %t.o
 ; RUN: llvm-lto2 run %t.o %loadbye -wave-goodbye -o %t -r %t.o,somefunk,plx -r %t.o,junk,plx 2>&1 | FileCheck %s
 ; RUN: llvm-lto2 run %t.o %loadbye %loadnewpmbye -wave-goodbye -use-new-pm -o %t -r %t.o,somefunk,plx -r %t.o,junk,plx 2>&1 | FileCheck %s
 ; RUN: llvm-lto2 run %t.o %loadbye %loadnewpmbye -opt-pipeline="goodbye" -wave-goodbye -use-new-pm -o %t -r %t.o,somefunk,plx -r %t.o,junk,plx 2>&1 | FileCheck %s
 ; REQUIRES: plugins, examples
+; UNSUPPORTED: windows
 ; CHECK: Bye
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 @junk = global i32 0
 
 define i32* @somefunk() {
   ret i32* @junk
 }