The pass written in the previous recipe, Writing your own LLVM pass, is ready to be run on the LLVM IR. This pass needs to be loaded dynamically for the opt tool to recognize and execute it.
Do the following steps:
- Write the C test code in the
sample.cfile, which we will convert into an.llfile in the next step:$ vi sample.c int foo(int n, int m) { int sum = 0; int c0; for (c0 = n; c0 > 0; c0--) { int c1 = m; for (; c1 > 0; c1--) { sum += c0 > c1 ? 1 : 0; } } return sum; } - Convert the C test code into LLVM IR using the following command:
$ clang –O0 –S –emit-llvm sample.c –o sample.llThis will generate a
sample.llfile. - Run the new pass with the opt tool, as follows:
$ opt -load (path_to_.so_file)/FuncBlockCount.so -funcblockcount sample.ll
The output will look something like this:
Function foo
As seen in the preceding code, the shared object loads dynamically into the opt command-line tool and runs the pass. It goes over the function and displays its name. It does not modify the IR. Further enhancement in the new pass is demonstrated in the next recipe.
- To know more about the various types of the Pass class, visit http://llvm.org/docs/WritingAnLLVMPass.html#pass-classes-and-requirements
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