[CMake] Look up target subcomponents in LLVM_AVAILABLE_LIBS

[aaronpuchert]

Summary

In an installation using the all-contained libLLVM.so, individual
components are not available as targets, so we have to look them up in
LLVM_AVAILABLE_LIBS just like llvm_map_components_to_libnames does it.
Here I don't think we need the capitalized names though because we know
the right capitalization. But I might be wrong.

This is required by dragonffi, who call llvm_map_components_to_libnames
on a list containing ${LLVM_NATIVE_ARCH}. Downstream bug report:
https://bugzilla.opensuse.org/show_bug.cgi?id=1180748.

[aaronpuchert]

Ping.

[dsanders]

I'm not familiar with the behaviour of cmake exports so I don't feel able to review this but FWIW, since it goes on to check libraries against LLVM_AVAILABLE_LIBS line 289 it doesn't sound wrong to check against that a little earlier.

I don't think it changes whether you run into the problem or not but is there a reason dragonffi specifies ${LLVM_NATIVE_ARCH} rather than native?

[aaronpuchert]

In D96670#2819765, @dsanders wrote:

I'm not familiar with the behaviour of cmake exports so I don't feel able to review this

I think I saw your name in the git blame. There isn't much to know about the exports here, except that there is the possibility to ship a big shared library that contains all LLVM components, and Linux distributions want LLVM users to link against that instead of the individual component libraries. So often the component libraries are not even shipped.

Subsequently, some of the targets that exist in-tree are not available to external users. That's not a problem, as llvm_map_components_to_libnames maps these components to the shared library in that case, but without this patch it doesn't expand pseudo-components when their constituents are not targets.

I don't think it changes whether you run into the problem or not but is there a reason dragonffi specifies ${LLVM_NATIVE_ARCH} rather than native?

Not sure. But it seems to me as well that it wouldn't change anything, one is just an alias for the other.

[aaronpuchert]

Ping.

[aaronpuchert]

Ping.

[aaronpuchert]

Doesn't seem like I can get this reviewed, so let me just land it and see if someone complains.

[beanz]

Woah!

“I can’t find someone to review this so I’m just going to merge it” is not okay.

I apologize for not reviewing it earlier, but c’mon… that’s not how the community operates.

In terms of the change itself, the logic looks fine, but you should use the CMake “if(NOT … IN_LIST …)” formulation instead of find and checking indexes. It is more concise and more clearly expresses what you’re doing.

[aaronpuchert]

Yeah, I don't usually do this. But this has been sitting for a very long time with a couple of pings and no attention.

In D96670#4072350, @beanz wrote:

In terms of the change itself, the logic looks fine, but you should use the CMake “if(NOT … IN_LIST …)” formulation instead of find and checking indexes. It is more concise and more clearly expresses what you’re doing.

Thanks for the hint! I thought there must be an easier way, but you can find this pattern all over the code. Maybe you can have a look at D142405. It was a bit tedious and only covers llvm/cmake for now. But it definitely reads a lot better.

[beanz]

In D96670#4074988, @aaronpuchert wrote:

Yeah, I don't usually do this. But this has been sitting for a very long time with a couple of pings and no attention.

The review didn't have great reviewers selected. Adding additional reviewers or pinging people on Discord would have been a better approach. I often lose track of commit emails, but respond better to IM pings.

In D96670#4074988, @aaronpuchert wrote:

Thanks for the hint! I thought there must be an easier way, but you can find this pattern all over the code. Maybe you can have a look at D142405. It was a bit tedious and only covers llvm/cmake for now. But it definitely reads a lot better.

Will do.

llvm/cmake/modules/LLVM-Config.cmake

 endfunction(llvm_map_components_to_libraries)
 
 # Expand pseudo-components into real components.
 # Does not cover 'native', 'backend', or 'engine' as these require special
 # handling. Also does not cover 'all' as we only have a list of the libnames
 # available and not a list of the components.
 function(llvm_expand_pseudo_components out_components)
   set( link_components ${ARGN} )
+  if(NOT LLVM_AVAILABLE_LIBS)
+    # Inside LLVM itself available libs are in a global property.
+    get_property(LLVM_AVAILABLE_LIBS GLOBAL PROPERTY LLVM_LIBS)
+  endif()
   foreach(c ${link_components})
     # add codegen, asmprinter, asmparser, disassembler
     list(FIND LLVM_TARGETS_TO_BUILD ${c} idx)
     if( NOT idx LESS 0 )
-      if( TARGET LLVM${c}CodeGen )
+      list(FIND LLVM_AVAILABLE_LIBS LLVM${c}CodeGen lib_idx)
+      if( lib_idx GREATER_EQUAL 0 )
         list(APPEND expanded_components "${c}CodeGen")
       else()
-        if( TARGET LLVM${c} )
+        list(FIND LLVM_AVAILABLE_LIBS LLVM${c} lib_idx)
+        if( lib_idx GREATER_EQUAL 0 )
           list(APPEND expanded_components "${c}")
         else()
           message(FATAL_ERROR "Target ${c} is not in the set of libraries.")
         endif()
       endif()
-      if( TARGET LLVM${c}AsmPrinter )
-        list(APPEND expanded_components "${c}AsmPrinter")
-      endif()
-      if( TARGET LLVM${c}AsmParser )
-        list(APPEND expanded_components "${c}AsmParser")
-      endif()
-      if( TARGET LLVM${c}Desc )
-        list(APPEND expanded_components "${c}Desc")
-      endif()
-      if( TARGET LLVM${c}Disassembler )
-        list(APPEND expanded_components "${c}Disassembler")
-      endif()
-      if( TARGET LLVM${c}Info )
-        list(APPEND expanded_components "${c}Info")
-      endif()
-      if( TARGET LLVM${c}Utils )
-        list(APPEND expanded_components "${c}Utils")
+      foreach(subcomponent IN ITEMS AsmPrinter AsmParser Desc Disassembler Info Utils)
+        list(FIND LLVM_AVAILABLE_LIBS LLVM${c}${subcomponent} lib_idx)
+        if( lib_idx GREATER_EQUAL 0 )
+          list(APPEND expanded_components "${c}${subcomponent}")
         endif()
+      endforeach()
     elseif( c STREQUAL "nativecodegen" )
-      if( TARGET LLVM${LLVM_NATIVE_ARCH}CodeGen )
-        list(APPEND expanded_components "${LLVM_NATIVE_ARCH}CodeGen")
-      endif()
-      if( TARGET LLVM${LLVM_NATIVE_ARCH}Desc )
-        list(APPEND expanded_components "${LLVM_NATIVE_ARCH}Desc")
-      endif()
-      if( TARGET LLVM${LLVM_NATIVE_ARCH}Info )
-        list(APPEND expanded_components "${LLVM_NATIVE_ARCH}Info")
+      foreach(subcomponent IN ITEMS CodeGen Desc Info)
+        list(FIND LLVM_AVAILABLE_LIBS LLVM${LLVM_NATIVE_ARCH}${subcomponent} lib_idx)
+        if( lib_idx GREATER_EQUAL 0 )
+          list(APPEND expanded_components "${LLVM_NATIVE_ARCH}${subcomponent}")
         endif()
+      endforeach()
     elseif( c STREQUAL "AllTargetsCodeGens" )
       # Link all the codegens from all the targets
       foreach(t ${LLVM_TARGETS_TO_BUILD})
         if( TARGET LLVM${t}CodeGen)
           list(APPEND expanded_components "${t}CodeGen")
         endif()
       endforeach(t)
     elseif( c STREQUAL "AllTargetsAsmParsers" )
       # Link all the asm parsers from all the targets
       foreach(t ${LLVM_TARGETS_TO_BUILD})
-        if( TARGET LLVM${t}AsmParser )
+        list(FIND LLVM_AVAILABLE_LIBS LLVM${t}AsmParser lib_idx)
+        if( lib_idx GREATER_EQUAL 0 )
           list(APPEND expanded_components "${t}AsmParser")
         endif()
       endforeach(t)
     elseif( c STREQUAL "AllTargetsDescs" )
       # Link all the descs from all the targets
       foreach(t ${LLVM_TARGETS_TO_BUILD})
-        if( TARGET LLVM${t}Desc )
+        list(FIND LLVM_AVAILABLE_LIBS LLVM${t}Desc lib_idx)
+        if( lib_idx GREATER_EQUAL 0 )
           list(APPEND expanded_components "${t}Desc")
         endif()
       endforeach(t)
     elseif( c STREQUAL "AllTargetsDisassemblers" )
       # Link all the disassemblers from all the targets
       foreach(t ${LLVM_TARGETS_TO_BUILD})
-        if( TARGET LLVM${t}Disassembler )
+        list(FIND LLVM_AVAILABLE_LIBS LLVM${t}Disassembler lib_idx)
+        if( lib_idx GREATER_EQUAL 0 )
           list(APPEND expanded_components "${t}Disassembler")
         endif()
       endforeach(t)
     elseif( c STREQUAL "AllTargetsInfos" )
       # Link all the infos from all the targets
       foreach(t ${LLVM_TARGETS_TO_BUILD})
-        if( TARGET LLVM${t}Info )
+        list(FIND LLVM_AVAILABLE_LIBS LLVM${t}Info lib_idx)
+        if( lib_idx GREATER_EQUAL 0 )
           list(APPEND expanded_components "${t}Info")
         endif()
       endforeach(t)
     elseif( c STREQUAL "AllTargetsMCAs" )
       # Link all the TargetMCAs from all the targets
       foreach(t ${LLVM_TARGETS_TO_BUILD})
         if( TARGET LLVM${t}TargetMCA )
           list(APPEND expanded_components "${t}TargetMCA")