llvm replace a function with another one

Question

I am trying to replace a function call with another one. e.g. here is the code with 3 functions - print1, print2 and main: ``` #include extern "C" { int print1() { printf("Inside print1 "); return 0xdeadbeef; } int print2() { printf("Inside print2 "); return 0xbeefdead; } int main(void) { return print1(); } }" ``` My goal is to replace use of print1 (in main) with print2. I compile the above code into an llvm::Module* (called main in the code below) and then create an execution engine out of it. ``` std::string errMsg; llvm::ExecutionEngine *ee = llvm::EngineBuilder( main ).setErrorStr( &errMsg ).create(); ASSERT_NE( ee, nullptr )<<"Execution engine is nullptr:"<getFunction( "print1" ); llvm::Functio…

Accepted Answer

If the compiler were to inline `print1` in `main`, the function would never actually be called; Instead, `main` would have its own private version of `print1`'s code pasted in. Since it doesn't actually have to refer to the shared `print1` anymore, swapping in `print2` might not affect `main`'s behavior.

If you want to verify that this is the problem (and/or keep it from happening, if it is), try telling the compiler not to inline.

llvm replace a function with another one

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