[LLVMdev] Adding a module in a pass

[John Criswell]

On 8/9/11 6:49 AM, Bjorn Reese wrote:
> I have an optimization pass (FunctionPass) where I need to add global
> constructors.
>
> For cleaness sake I decided to add these in my own module. My module
> is created in my FunctionPass constructor:

This is not how I would do it.  A FunctionPass has doInitialization() 
and doFinalization() methods that you can implement thatcan operate on 
the whole module.  They are designed for exactly the situation you 
describe: your pass does some sort of local transform, but there's some 
global modifications it needs to do (add global constructors, add 
function prototypes, etc).

-- John T.

>
>     MyPass()
>       : FunctionPass(ID),
>         myModule("my_module", getGlobalContext())
>     {}
>
> I generate an llvm.global_ctor global variable in my module, and I add
> my global constructors there. This appears to be correct. Here is a
> dump of the module after the pass:
>
>     ; ModuleID = 'my_module'
>
>     @my_literal = internal constant [6 x i8] c"Hello\00"
>     @llvm.global_ctors = appending global [1 x { i32, void ()* }] [void
> () { i32 65535, void ()* @my_global_constructor }]
>
>     define void @my_global_constructor() {
>       %puts = call i32 @puts(i8* getelementptr inbounds ([6 x i8]*
> @my_literal, i32 0, i32 0))
>     }
>
>     declare i32 @puts(i8* nocapture) nounwind
>
> My problem is that this module is not linked into the executable.
>
> Do I need to insert the module somewhere?
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