[Sprint 3] Add function inline pass

[sharaelong]

Overview

This pull request implements function inline pass. Inliner pass is implemented in llvm already, but I tried to add architecture-dependent conditions for deciding whether this function has to be inlined or not. Specifically I considered these 3 properties:

• Function call is relatively cheap in our architecture
• Instruction count in function
• Register pressure of function, since we can calculate exact number of colors from backend logic. However, due to limitations of LOC number in single PR, I delayed consideration of register pressure. Then finally, my function inline logic will consider two points:
• When function has less than 100 instructions
• Function which don't included in possible cycle call subgraph

Implementation

First iterate through all functions in module. Check basic inlining conditions and above criteria.

• Check function is just declaration
• Check function can be the part of some call subgraph cycle
• Callee is not indirect call, and check is just declaration
• call isInlineViable to check callee can be inlined
• If function has NoInline attribute, don't inline it.
• Check Number of function instruction For functions pass all this criteria can be considered as candidate of inline.

Unit tests

1. One of the most important usage of inline pass is inlining malloc_upto_8. First tests is responsible for this.
2. Check if cycle detection logic is well designed. functionA and functionB calls each other.
3. max calls fact internally. So only max has to be inlined in main function.

[sharaelong]

I found that usage of both heap2stack and functioninline pass makes runtime error in matmul2.

[willi19]

Today, we found out that error was due to two reason. First returning :all in heap2stack passed incorrect analysis to other pass. Second spilled register in main function are accessed by the sp register but heap2stack update the sp so this caused incorrect output. This can be fixed by changing heap2stack to allocated stack memory at the beginning of the program.

[germanium32]

Fairly simple logic(detecting block graph structure then inlining), so I have no doubt about this implementation.

LGTM!

[sharaelong]

I fixed bug that found on offline session: matmul2 main logic function is inlined even it is bigger than my threshold.

[sharaelong]

Fairly simple logic(detecting block graph structure then inlining), so I have no doubt about this implementation.

LGTM!

Actually, there was a bug!! haha... but it was subtle =)