Fix the special treatment for Homebrew

When using Homebrew packages, `static` needs to be linked with
`libLLVM` rather than a more specialised set of LLVM libraries. But this
only applies to Homebrew packages. This patch fixes how llvm-tutor
decides whether to use `libLLVM` or not.

.github/workflows/x86-darwin-llvm-from-sources.yml

@@ -29,10 +29,9 @@ jobs:
           cmake -G Ninja \
             -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS="clang" \
             -DLLVM_TARGETS_TO_BUILD="X86" -DLLVM_OPTIMIZED_TABLEGEN=ON \
-            -DLLVM_BUILD_LLVM_DYLIB=ON \
             ../llvm
           # Note that only the required tools are built
-          ninja clang opt lli not FileCheck LLVM
+          ninja clang opt lli not FileCheck
       - name: Install lit
         run: |
           sudo pip3 install lit

.github/workflows/x86-ubuntu-llvm-from-sources-static.yml

@@ -34,7 +34,6 @@ jobs:
           cmake -G Ninja \
             -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS="clang" \
             -DLLVM_TARGETS_TO_BUILD="host" -DLLVM_OPTIMIZED_TABLEGEN=ON \
-            -DLLVM_BUILD_LLVM_DYLIB=ON \
             -DLLVM_BUILD_EXAMPLES=On -DLLVM_MBASUB_LINK_INTO_TOOLS=On \
             ../llvm
           # Note that only the required tools are built

.github/workflows/x86-ubuntu-llvm-from-sources.yml

@@ -32,10 +32,9 @@ jobs:
           cmake -G Ninja \
             -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS="clang" \
             -DLLVM_TARGETS_TO_BUILD="X86" -DLLVM_OPTIMIZED_TABLEGEN=ON \
-            -DLLVM_BUILD_LLVM_DYLIB=ON \
             ../llvm
           # Note that only the required tools are built
-          ninja clang opt lli not FileCheck LLVM
+          ninja clang opt lli not FileCheck
       - name: Install lit
         run: |
           sudo apt-get install python3-setuptools

tools/CMakeLists.txt

@@ -1,3 +1,6 @@
+# TODO: Once LLVM 16 is released, replace `try_compile` with a test for
+# LLVM_ENABLE_LTO, see https://reviews.llvm.org/D134936.
+
 # DEFINE THE TARGET
 #==================
 set(static_SOURCES
@@ -14,25 +17,36 @@ target_include_directories(
 
 # DECIDE WHAT LIBRARIES TO LINK IN
 #=================================
-# The list of the libraries below is the required minimum. However, when using
-# LLVM from Homebrew your system linker might complain when using these:
+# The minimal list of the required LLVM libraries.
+set(libs LLVMCore LLVMPasses LLVMIRReader LLVMSupport)
+
+# The list above won't work when using LLVM from Homebrew. Indeed, your system
+# linker will most likely complain:
 # ```
 #   (...) Opaque pointers are only supported in -opaque-pointers mode (Producer: 'LLVM15.0.0' Reader: 'LLVM APPLE_1_1400.0.29.102_0')
 # ```
-# To work around this this, you can use `libLLVM` instead. That solves the
-# problem because:
+# That's more or less due to Homebrew packages being built with LTO (i.e.
+# LLVM_ENABLE_LTO set to "ON") To work around this, you can use `libLLVM`
+# instead. That solves the problem because:
 #  * `libLLVM` is always a dynamic library (and the problem above is only
 #    triggered for static libs)
 #  * libLLVM includes all LLVM libraries (i.e. all the libraries listed below
 #    _and more_)
-set(libs "LLVMCore LLVMPasses LLVMIRReader LLVMSupport")
-
-try_compile(testMinimalCompilation "${CMAKE_BINARY_DIR}/temp" SOURCES ${static_SOURCES})
+# Check whether the default set-up is sufficient ...
+try_compile(testMinimalCompilation "${CMAKE_BINARY_DIR}/temp"
+  SOURCES ${static_SOURCES}
+  LINK_LIBRARIES ${libs}
+  CMAKE_FLAGS 
+    "-DINCLUDE_DIRECTORIES=${CMAKE_CURRENT_SOURCE_DIR}/../include;${LLVM_INCLUDE_DIRS}"
+    "-DLINK_DIRECTORIES=${LLVM_LIBRARY_DIRS}")
 
+# ... if not, use libLLVM
 if(NOT ${testMinimalCompilation})
-  set(libs "LLVM")
+  set(libs LLVM)
 endif()
 
+# ADD THE LIBRARIES TO LINK
+#==========================
 target_link_libraries(static
   ${libs}
   )