Hi everyone,
I am kind of a newbie here, working on llvm as a undergraduate student and I am struggling about some situations. Yet I can write meaningless passes, working tools by copying or trying to porting from llvm source and know how to build them. I am searching on the web, using https://llvm.org/doxygen to understand some functions, classes and how I can integrate these kind of things in my experimental codes but I think that I can’t go any further now that’s why I am writing this e-mail and probably more comes for different questions.
I am trying to write a tool which will get target triple as a command option and a C or C++ code, will emit and change LLVM IR code (maybe adding a pass or meaningless operation for now 
) inside, will emit and change object code from changed LLVM IR, and lastly will give output as an executable file.
Example tool in summary as I thought:
Usage (I can add some command line options later):
mytool --triple riscv32 example.c
Sequence of this complete tool:
Run Tool → Get Target Triple → Emit LLVM IR code from source code → Change LLVM IR code → Emit Object Code → Change Object Code → Give Executable File Output
For this, firstly I thought implement to get file and target triple (If I am mistaken or incomplete you can warn):
#include "llvm/Support/CommandLine.h"
static cl::list<std::string>
InputFilenames(cl::Positional, cl::desc("<input files>"),cl::ZeroOrMore);
extern cl::opt<std::string> TripleName;
cl::opt<std::string>
llvm::TripleName("triple", cl::desc("target triple"));
Suppose that I did more coding and get source code file in main function, after that how can I emit LLVM IR or object code inside and apply on some operations?
I am asking this because for example we can use a pass in command line as:
opt -load libMyPass.so -mypass example.ll -o output.ll
or in clang with -Xclang -load -Xclang option.
or this is more proper example:
clang -mem2reg example.ll -o output.ll
And we can also use these passes in our codes (in other passes or tools):
static std::unique_ptr<legacy::FunctionPassManager> TheFPM;
TheFPM->add(createPromoteMemoryToRegisterPass());
TheFPM->run(*TheFunction);
(TheFunction should be declared before.)
or maybe addPass function (I am not sure.)
https://llvm.org/doxygen/classllvm_1_1PassManager.html#a314ff184ce4ace8801e1158ef909e22e
or like using an analysis pass inside another different pass:
void LegacyAnotherPass::getAnalysisUsage(AnalysisUsage &Info) const {
Info.addRequired<LegacyMyAnalysisPass>();
}
I thought we could other command line operations inside our code as this. I am trying to find a function for my desire. For example as in the pass example above:
clang -S -emit-llvm example.c -o example.ll
clang -c example.ll -o example.o
And code equivalent (extremely making up ):
for llvm ir:
llvmir = file.getLLVMIRCode();
for object code:
objcode = llvmir.getObjectCode();
Is there a way like this in simply and how I can?
Maybe you can say “write a bash script and do operations step by step” but I want to write this complete tool using llvm and its functions inside. If you can answer I will be satisfied and please don’t forget I am newbie if I am mistaken on some points.
Thanks,
Seyyid