Machine IR (MIR)

quoted from: Testing Individual Code Generation Passes

The run-pass option in llc allows you to create MIR tests that invoke just a single code generation pass. When this option is used, llc will parse an input MIR file, run the specified code generation pass, and print the resulting MIR to the standard output stream.

You can generate an input MIR file for the test by using the stop-after option in llc. For example, if you would like to write a test for the post register allocation pseudo instruction expansion pass, you can specify the machine copy propagation pass in the stop-after option, as it runs just before the pass that we are trying to test:

llc -stop-after machine-cp bug-trigger.ll > test.mir

After generating the input MIR file, you’ll have to add a run line that uses the -run-pass option to it. In order to test the post register allocation pseudo instruction expansion pass on X86-64, a run line like the one shown below can be used:

# RUN: llc -run-pass postrapseudos -march=x86-64 %s -o /dev/null | FileCheck %s

The MIR files are target dependent, so they have to be placed in the target specific test directories. They also need to specify a target triple or a target architecture either in the run line or in the embedded LLVM IR module