-
-
- What is this __main() call that gets inserted into - main()?
- What is this llvm.global_ctors and _GLOBAL__I__tmp_webcompile... stuff that happens when I #include <iostream>? @@ -89,7 +99,7 @@
Yes. The modified source distribution must retain the copyright notice and follow the three bulletted conditions listed in the LLVM license.
+href="http://llvm.org/releases/1.3/LICENSE.TXT">LLVM license.Some porting problems may exist in the following areas:
-
-
- The GCC front end code is not as portable as the LLVM suite, so it may not - compile as well on unsupported platforms. + compile as well on unsupported platforms.
- The LLVM build system relies heavily on UNIX shell tools, like the Bourne - Shell and sed. Porting to systems without these tools (MacOS 9, Plan 9) will - require more effort. - + Shell and sed. Porting to systems without these tools (MacOS 9, Plan 9) + will require more effort.
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?
@@ -231,21 +223,23 @@ 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.
+ 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.
-
+ 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.
@@ -317,11 +312,18 @@ 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:
@@ -383,6 +386,55 @@ which list dependencies for source files, and rebuild: rebuilding.
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 + java module. There is no documentation on this yet so + you'll need to download the code, compile it, and try it.
+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.
+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 semantic analysis. There is, however, a mostly + implemented configuration-driven + compiler driver which simplifies the task + of running optimizations, linking, and executable generation.
+To work around this, perform the following steps:
--
-
- - Make sure the CC and CXX environment variables contains the full path to the - LLVM GCC front end. - +
- Make sure the CC and CXX environment variables contains the full path to + the LLVM GCC front end. -
- - Make sure that the regular C compiler is first in your PATH. - +
- Make sure that the regular C compiler is first in your PATH. -
- - Add the string "-Wl,-native" to your CFLAGS environment variable. - +
- Add the string "-Wl,-native" to your CFLAGS environment variable.
-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
@@ -461,33 +509,85 @@ 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.
+ LLVM Compiler Infrastructure
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