Figure out all debugging information representations of statements

[dianqk]

#142771 has eliminated the simple reference assignment statement. We should figure out more about how to represent others statements via debugging information.

Steps

• How to represent projection of place, i.e., _1.1 = &_2;?
• How to represent other rvalues?
• Other non-assignment statements?

Implementation history

#142771 has implemented _1 = &_2.

Related Resources

• Debug Info Assignment Tracking
• Source Level Debugging with LLVM

[cjgillot]

How to represent projection of place, i.e., _1.1 = &_2;?

There is already code in rustc_codegen_ssa to support this. We use this for projections inside VarDebugInfo.