Some porting problems may exist in the following areas:
I compile the code, and I get some error about /localhome.
-There are several possible causes for this. The first is that you didn't set -a pathname properly when using configure, and it defaulted to a -pathname that we use on our research machines.
- -Another possibility is that we hardcoded a path in our Makefiles. If you see -this, please email the LLVM bug mailing list with the name of the offending -Makefile and a description of what is wrong with it.
- -The configure script finds the right C compiler, but it uses the LLVM linker from a previous build. What do I do?
@@ -238,21 +226,23 @@ if it's grabbing the wrong linker/assembler/etc, there are two ways to fix it:Adjust your PATH environment variable so that the correct - program appears first in the PATH. This may work, but may not be - convenient when you want them first in your path for other - work.
Run configure with an alternative PATH that is - correct. In a Borne compatible shell, the syntax would be:
- -PATH=[the path without the bad program] ./configure ...
+ correct. In a Borne compatible shell, the syntax would be: + ++% PATH=[the path without the bad program] ./configure ... ++
This is still somewhat inconvenient, but it allows configure - to do its work without having to adjust your PATH - permanently.
I've updated my source tree from CVS, and now my build is trying to use a -file/directory that doesn't exist.
+I've updated my source tree from Subversion, and now my build is trying to +use a file/directory that doesn't exist.
If the Makefile already exists in your object tree, you can just run the following command in the top level directory of your object tree:
-./config.status <relative path to Makefile>
+
% ./config.status <relative path to Makefile>+
If the Makefile is new, you will have to modify the configure script to copy it over.
@@ -324,11 +315,18 @@ clean and then make in the directory that fails to build.For example, if you built LLVM with the command:
-gmake ENABLE_PROFILING=1 +
% gmake ENABLE_PROFILING=1+
...then you must run the tests with the following commands:
-cd llvm/test
gmake ENABLE_PROFILING=1
+% cd llvm/test +% gmake ENABLE_PROFILING=1 ++
This is a bug in GCC, and - affects projects other than LLVM. Try upgrading or downgrading your GCC.
+affects projects other than LLVM. Try upgrading or downgrading your GCC.After CVS update, rebuilding gives the error "No rule to make target".
+After Subversion update, rebuilding gives the error "No rule to make +target".
If the error is of the form:
gmake[2]: *** No rule to make target `/path/to/somefile', needed by `/path/to/another/file.d'.+
Stop. -
This may occur anytime files are moved within the CVS repository or removed -entirely. In this case, the best solution is to erase all .d files, -which list dependencies for source files, and rebuild:
+This may occur anytime files are moved within the Subversion repository or +removed entirely. In this case, the best solution is to erase all +.d files, which list dependencies for source files, and rebuild:
@@ -390,42 +389,107 @@ which list dependencies for source files, and rebuild: rebuilding.
What source languages are supported?
llvmc is experimental and isn't really supported. We suggest +using llvm-gcc instead.
+LLVM currently has full support for C and C++ source languages. These are available through a special version of GCC that LLVM calls the C Front End
There is an incomplete version of a Java front end available in the - llvm-java CVS repository. There is no documentation on this yet so + java module. There is no documentation on this yet so you'll need to download the code, compile it, and try it.
-In the examples/BFtoLLVM directory is a translator for the - BrainF*** language (2002 Language Specification).
-In the projects/Stacker directory is a compiler and runtime +
In the stacker module is a compiler and runtime library for the Stacker language, a "toy" language loosely based on Forth.
The PyPy developers are working on integrating LLVM into the PyPy backend so that PyPy language can translate to LLVM.
What support is there for a higher level source language constructs for - building a compiler?
+ + +Your compiler front-end will communicate with LLVM by creating a module in + the LLVM intermediate representation (IR) format. Assuming you want to + write your language's compiler in the language itself (rather than C++), + there are 3 major ways to tackle generating LLVM IR from a front-end:
+If you go with the first option, the C bindings in include/llvm-c should + help a lot, since most languages have strong support for interfacing with + C. The most common hurdle with calling C from managed code is interfacing + with the garbage collector. The C interface was designed to require very + little memory management, and so is straightforward in this regard.
+Currently, there isn't much. LLVM supports an intermediate representation which is useful for code representation but will not support the high level (abstract syntax tree) representation needed by most compilers. There are no - facilities for lexical nor semantica analysis. There is, however, a mostly + facilities for lexical nor semantic analysis. There is, however, a mostly implemented configuration-driven compiler driver which simplifies the task of running optimizations, linking, and executable generation.
-You might be interested in following the progress of the HLVM Project which is attempting to address these - issues.
To work around this, perform the following steps:
--This will allow the gccld linker to create a native code executable instead of -a shell script that runs the JIT. Creating native code requires standard -linkage, which in turn will allow the configure script to find out if code is -not linking on your system because the feature isn't available on your system. -
+This will allow the llvm-ld linker to create a native code executable +instead of shell script that runs the JIT. Creating native code requires +standard linkage, which in turn will allow the configure script to find out if +code is not linking on your system because the feature isn't available on your +system.The only way this can happen is if you haven't installed the runtime library. To correct this, do:
+ +- % cd llvm/runtime - % make clean ; make install-bytecode +% cd llvm/runtime +% make clean ; make install-bytecode
@@ -504,33 +564,85 @@ code that you desire.
-The __main call is inserted by the C/C++ compiler in order to guarantee -that static constructors and destructors are called when the program starts up -and shuts down. In C, you can create static constructors and destructors by -using GCC extensions, and in C++ you can do so by creating a global variable -whose class has a ctor or dtor. +Can I use LLVM to convert C++ code to C code?
+-The actual implementation of __main lives in the -llvm/runtime/GCCLibraries/crtend/ directory in the source-base, and is -linked in automatically when you link the program. +
Yes, you can use LLVM to convert code from any language LLVM supports to C. +Note that the generated C code will be very low level (all loops are lowered +to gotos, etc) and not very pretty (comments are stripped, original source +formatting is totally lost, variables are renamed, expressions are regrouped), +so this may not be what you're looking for. However, this is a good way to add +C++ support for a processor that does not otherwise have a C++ compiler.
+ +Use commands like this:
+ +Compile your program as normal with llvm-g++:
+ ++% llvm-g++ x.cpp -o program +
or:
+ ++% llvm-g++ a.cpp -c +% llvm-g++ b.cpp -c +% llvm-g++ a.o b.o -o program ++
With llvm-gcc3, this will generate program and program.bc. The .bc + file is the LLVM version of the program all linked together.
Convert the LLVM code to C code, using the LLC tool with the C + backend:
+ ++% llc -march=c program.bc -o program.c ++
Finally, compile the C file:
+ ++% cc x.c ++
Note that, by default, the C backend does not support exception handling. If +you want/need it for a certain program, you can enable it by passing +"-enable-correct-eh-support" to the llc program. The resultant code will use +setjmp/longjmp to implement exception support that is correct but relatively +slow.
+ +Also note: this specific sequence of commands won't work if you use a +function defined in the C++ runtime library (or any other C++ library). To +access an external C++ library, you must manually compile libstdc++ to LLVM +bitcode, statically link it into your program, then use the commands above to +convert the whole result into C code. Alternatively, you can compile the +libraries and your application into two different chunks of C code and link +them.
+ +
+int X() { int i; return i; }
+
Is compiled to "ret int undef" because "i" never has a value -specified for it. -
+Is compiled to "ret i32 undef" because "i" never has +a value specified for it.