[all-commits] [llvm/llvm-project] 45526d: [CMAKE] Provide default location for llvm-lit for ...

[stephenneuendorffer via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 45526d29a5b2cf126b83ada3991921970007d16f
      https://github.com/llvm/llvm-project/commit/45526d29a5b2cf126b83ada3991921970007d16f
  Author: Stephen Neuendorffer <stephen.neuendorffer at xilinx.com>
  Date:   2020-04-22 (Wed, 22 Apr 2020)

  Changed paths:
    M llvm/cmake/modules/CMakeLists.txt
    M llvm/cmake/modules/LLVMConfig.cmake.in

  Log Message:
  -----------
  [CMAKE] Provide default location for llvm-lit for out-of-tree users.

Several external build users contain some heuristics for finding llvm-lit.
There are several cases we need to worry about:
- External builds against a build tree (with LLVM_BUILD_UTILS)
- External builds against an install tree (with LLMV_BUILD_UTIL
  and LLVM_INSTALL_UTILS)
- External builds against some location which doesn't have an
  llvm-lit, but llvm-lit is available through some other means, such
  as an available source tree, or a packager provided llvm-lit.

For the third case, LLVM_EXTERNAL_LIT suffices, but in other cases
there's no standard way to find llvm-lit.  It seems like each user
cooks their own heuristics:

- clang tries to look in the LLVM source tree, and failing that falls
  back to looking for a packaged llvm-lit.
- libcxx tries to look in the LLVM source tree, which might come from
  llvm-config or be explicitly specified.

This patch is a first stop to solving this by providing a default location
for llvm-lit using LLVM_DEFAULT_EXTERNAL_LIT.  The expectation is that
future patches can clean up users like clang and libcxx to rely
on this mechanism for out-of-tree builds.

Differential Revision: https://reviews.llvm.org/D77110