[LLVMdev] [CMake] Generated LLVMConfig.cmake and LLVMExports.cmake broken under Visual Studio 2015

[Dan Liew]

Hi,

Myself and a colleague of mine are trying to use LLVM's exported
targets [1] on trunk and I've noticed that the generated CMake files
(LLVMConfig.cmake and LLVMExport.cmake) are broken when trying to use
Visual Studio 2015 (using CMake 3.2.1).

## Broken target properties in LLVMExports.cmake

LLVM itself builds fine but when our project tries to do
``find_package(LLVM)`` we get the following error message (see [2] for
context).


```
-- Looking for LLVM
CMake Warning (dev) at
C:/Users/me/Documents/halide/llvm-build/share/llvm/cmake/LLVMExports.cmake:232
(set_target_properties):
  Syntax error in cmake code at

    C:/Users/me/Documents/halide/llvm-build/share/llvm/cmake/LLVMExports.cmake:233

  when parsing string

    LLVMObject;LLVMSupport;C:\Program Files (x86)\Microsoft Visual
Studio 14.0\DIA SDK\lib\diaguids.lib

  Invalid escape sequence \P

  Policy CMP0010 is not set: Bad variable reference syntax is an error.  Run
  "cmake --help-policy CMP0010" for policy details.  Use the cmake_policy
  command to set the policy and suppress this warning.
Call Stack (most recent call first):
  c:/Users/me/Documents/halide/llvm-build/share/llvm/cmake/LLVMConfig.cmake:174
(include)
  CMakeLists.txt:14 (find_package)
This warning is for project developers.  Use -Wno-dev to suppress it.
```

The issue is the that that generated LLVMExports.cmake file has this in it

```
# Create imported target LLVMDebugInfoPDB
add_library(LLVMDebugInfoPDB STATIC IMPORTED)

set_target_properties(LLVMDebugInfoPDB PROPERTIES
  INTERFACE_LINK_LIBRARIES "LLVMObject;LLVMSupport;C:\Program Files
(x86)\Microsoft Visual Studio 14.0\DIA SDK\lib\diaguids.lib"
)
```

The problem is that the path to diaguids.lib is a windows path and not
a CMake style path so the backslashes get interpreted as escape
sequences.

I think this is a bug in CMake.

@Brad: Do you agree?


## Broken paths in LLVMConfig.cmake

This is a minor issue but I'm not sure if this a bug or an artifact of
using Visual Studio but some of the paths specified in
LLVMConfig.cmake are not real paths because they contain
``$(Configuration)``.

```
set(LLVM_BUILD_LIBRARY_DIR
"C:/Users/alexander.APRELEV/Documents/halide/llvm-build/$(Configuration)/lib")
...
set(LLVM_TOOLS_BINARY_DIR
"C:/Users/alexander.APRELEV/Documents/halide/llvm-build/$(Configuration)/bin")
```

The problem is that I was trying to check if

${LLVM_TOOLS_BINARY_DIR}/clang${CMAKE_EXECUTABLE_SUFFIX}

exists at configure time (which works on OSX and Linux) but this fails
when using Visual Studio because ``$(Configuration)`` is in the path.

Is this intentional?

[1] http://llvm.org/docs/CMake.html#embedding-llvm-in-your-project
[2] https://github.com/halide/Halide/pull/825

Thanks,
Dan.