[llvm-dev] Understanding LLVM Optimization (Rpass=inline)

[praveen via llvm-dev]

Dear LLVM community :-)

I'm a novice in compiler principles and optimization, I'm currently 
working with some example code to see what && how LLVM optimization is 
doing to generate good machine code. While working  I find some 
functions are being inlined by llvm and some are not, but I don't know 
the internals of optimization so I can't able to figure  the reasons and 
rationale behind them.

For example:

struct value{

int set(){} // Function does nothing!

};

void foo () {} // Function does nothing!

void func( ) {

value obj;

obj.set();

foo();

}

Compiling with command  "clang++ -O2 -std=c++11 
-stdlib=libc++/__//_*-Rpass=inline*_/ name.cpp prints

only obj.set() was inlined but not foo(). I don't understand the 
rationale behind this (both are empty functions right ?). Why LLVM not 
inlining the function "foo" ?

Could you please share some pointers (videos or blogs) which explains 
the design of llvm optimizations :-). And also what is mean by _/cost 
and threshold in inlining functions?/_/like (cost=always and 
cost=never). /_/
/_

Next,
_//_

Clang documentation (here 
<https://clang.llvm.org/docs/UsersManual.html#cmdoption-wambiguous-member-template>) 
mentions that -_/Wambiguous-member-template/_ warning _is defaulted to 
on_. But when I actually compile the same code as in documentation it 
doesn't throw up any warnings. Is the documentation is out-dated for 
clang 8.0.0 ?

Software details :

Clang 8.0.0 , Linux mint.

Hardware details:

X86-64 bit.

Could you please share your knowledge for the above questions ? it is a 
great help to me

Thank you very much for your time,

PreeJackie

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