-In order to find libcrtend.a, you must have the directory in which it lives in -your LLVM_LIB_SEARCH_PATH environment variable. For the binary distribution of -the LLVM GCC front end, this will be the full path of the bytecode-libs -directory inside of the LLVM GCC distribution. +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 ++
+How can I disable all optimizations when compiling code using the LLVM GCC front end?
+Passing "-Wa,-disable-opt -Wl,-disable-opt" will disable *all* cleanup and +optimizations done at the llvm level, leaving you with the truly horrible +code that you desire. +
+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++:
+
+Convert the LLVM code to C code, using the LLC tool with the C +backend:
+
+Finally, compile the c file:
+
+
or:
+ ++ 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.
+ +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 bytecode, 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.
+ +-Where did all of my code go?? -
-If you are using the LLVM demo page, you may often wonder what happened to all -of the code that you typed in. Remember that the demo script is running the -code through the LLVM optimizers, so if your code doesn't actually do anything -useful, it might all be deleted. -
- --To prevent this, make sure that the code is actually needed. For example, if -you are computing some expression, return the value from the function instead of -leaving it in a local variable. If you really want to constrain the optimizer, -you can read from and assign to volatile global variables. -
-What is this llvm.global_ctors and _GLOBAL__I__tmp_webcompile... stuff that happens when I #include <iostream>?
@@ -544,6 +637,51 @@ instead of iostreams to print values.+If you are using the LLVM demo page, you may often wonder what happened to all +of the code that you typed in. Remember that the demo script is running the +code through the LLVM optimizers, so if your code doesn't actually do anything +useful, it might all be deleted. +
+ ++To prevent this, make sure that the code is actually needed. For example, if +you are computing some expression, return the value from the function instead of +leaving it in a local variable. If you really want to constrain the optimizer, +you can read from and assign to volatile global variables. +
++undef is the LLVM way of representing +a value that is not defined. You can get these if you do not initialize a +variable before you use it. For example, the C function:
+ +Is compiled to "ret int undef" because "i" never has a value +specified for it. +
+@@ -553,7 +691,7 @@ instead of iostreams to print values.
+ LLVM Compiler Infrastructure
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