[LLVMdev] Building llvm from source with clang instead of gcc

Edward Diener eldlistmailingz at tropicsoft.com
Sat Jan 5 09:48:49 PST 2013

On 01/05/2013 11:32 AM, Krzysztof Parzyszek wrote:
> On 1/5/2013 7:10 AM, Edward Diener wrote:
>> Is it possible to build llvm with a previous version of clang installed
>> as a binary ? If so, how do I get llvm/configure to use the binary
>> version of clang rather than gcc to build the latest version of llvm ?
> Set environment variables CC and CXX to point to the clang/clang++
> binaries before running configure.

Do I give the full path to the executable, or just the executable name
if it is already in the PATH, for those environment variables ?

It would have been much better if the environment variables were named
LLVM_CC and LLVM_CXX for the obvious reason that CC and CXX are very
common names.

I actually found out that llvm/configure will choose clang if it is
found in the path. This contradicts what is written at
http://llvm.org/docs/GettingStarted.html#requirements, where it says it
will use the first GCC it finds. Perhaps that explanation needs to be

Finally I found that if llvm/configure uses clang instead of gcc, it
invariably fails on my Linux distros because it is using the gcc
distributed included directories and an earlier version of clang will
often fail with these gcc header files. Once I force llvm/configure to
use gcc, building llvm/clang succeeds again.

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