[PATCH] D141581: [clang] Make clangBasic and clangDriver depend on LLVMTargetParser.

[Francesco Petrogalli via Phabricator via cfe-commits]

fpetrogalli added a comment.

@barannikov88  - Imam stuck with an incomplete explanation:

The issue raised by @mgorny is about stand-alone <https://llvm.org/docs/GettingStarted.html#stand-alone-builds> builds. In this build configuration, clang is built separately from LLVM, which is first build and installed in a folder.

When clang is build as a stand-alone project, clang does not have access to the cmake configuration of LLVM. Therefore it knows nothing about the tablegen target `RISCVTargetParserTableGen`.

The's why we see the following error when building stand-alone clang on `main`:

  CMake Error at /Users/fpetrogalli/projects/cpu-defs/install/lib/cmake/llvm/AddLLVM.cmake:536 (add_dependencies):
    The dependency target "RISCVTargetParserTableGen" of target
    "obj.clangBasic" does not exist.
  Call Stack (most recent call first):
    cmake/modules/AddClang.cmake:106 (llvm_add_library)
    lib/Basic/CMakeLists.txt:40 (add_clang_library)

I do not know why `LLVMTargetParser` (which is also specified in the cmake configuration of llvm) is instead recognised as a valid dependencies of clang on some LLVM library. Maybe because cmake looks in the prefix folder where LLVM was installed and finds the object file of the library?

FWIW, I was able to reproduce the issue reported by @mgorny via the following script when run on `main`:

  #!/bin/sh
  
  build_llvm=`pwd`/build-llvm
  build_clang=`pwd`/build-clang
  installprefix=`pwd`/install
  llvm=`pwd`/llvm-project
  mkdir -p $build_llvm
  mkdir -p $installprefix
  
  cmake -G Ninja -S $llvm/llvm -B $build_llvm \
        -DLLVM_INSTALL_UTILS=ON \
        -DCMAKE_INSTALL_PREFIX=$installprefix \
        -DCMAKE_BUILD_TYPE=Release
  
  
  ninja -C $build_llvm install
  
  cmake -G Ninja -S $llvm/clang -B $build_clang \
        -DLLVM_EXTERNAL_LIT=$build_llvm/utils/llvm-lit \
        -DLLVM_ROOT=$installprefix

Given it was an issue that cmake itself was reporting (and not a build time failure), I thought that its disappearance after applying this patch was a signal thatI was doing the right thing.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D141581/new/

https://reviews.llvm.org/D141581