Implementing inline expansion

Question

I am curious to know how to implement inline expansion.

I am writing my own compiler just for fun and education.

I learn a lot by example so if someone can provide me an algorithm that does inlining that would help me a lot.

I prefer in C++ but the language doesn't matter.

The target language that I'm trying to write inlining for is JavaScript.

EDIT: Just to clarify, I am looking for ways to improve ShrinkSafe.
GWT inlines javascript functions so it is possible. GWT does inlining before the code is run.

score 2 · Answer 1 · answered Jun 09 '09 at 11:33

2

A common implementation is to do it in the optimization phase, as a rewrite rule. You replace the actual function call instruction by the called instructions (minus the return statement, naturally).

Next, you make sure that the peephole optimizer can eliminate the stack setup which preceded the call instruction and the callee's prologue which is now inlined. Similarly, you should make sure that the peephole optimizer can optimize the callees epilogue and the callers processing of the return value.

The biggest benefits of this are that it makes the instruction sequence contiguous in memory and the peephole optimizer typically saves you a bunch of stack push/pops.

answered Jun 09 '09 at 11:33

MSalters

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What heuristics should I use? How the code would look like? How do I check if the expression is a constant time expression? – the_drow Jun 09 '09 at 19:25
You're basically looking for common patterns like "PUSH Reg1; PUSH Reg2; POP Reg3; POP Reg1; " - the PUSH instructions are what remains from the caller argument setup; the POPs are from the inlined prologue. These 4 ins can be rewritten as "MOV Reg2 -> REG3", a single ins. The exact kind of patterns you'll find in the optimizer are of course determined by the instruction stream emitted by *your* compiler, so you're the expert on that. – MSalters Jun 10 '09 at 07:28

score 1 · Answer 2 · edited Nov 27 '13 at 16:46

In-lining is done after the code has been parsed into a tree.

for(int loop=1;loop <= 10;++loop)
{
    f(loop);
}

for-|
    --- (Init Code)---Assign--|
    |                         --- loop
    |                         |
    |                         --- 1
    --- (Condition)--- <= |
    |                     --- loop
    |                     |
    |                     --- 10
    --- (Post) --- ++ |
    |                 --- loop
    |
    --- (Body) Call |
                    --- (Function Name) f
                    |
                    --- (Parameter List)---Node1 -- loop
                                             |
                                           NULL

You will also have a parse tree for the function f.
To inline the function you need to create a duplicate of the tree for the function f. Then parse through the tree a replace all references to the parameter used in the function call with the variable (loop in this case). Once this is done. replace the 'Call' node in the above tree with the new tree you just created.

Implementing inline expansion

2 Answers2