[LLVMdev] freeing alloca'd variables before function exits

[Nadav Rotem]

On Nov 3, 2013, at 4:54 PM, Jeremy Lakeman <Jeremy.Lakeman at gmail.com> wrote:

> Stack colouring should be able to reuse the same stack space, if the live ranges of the pointers don't overlap. But I don't think anyone has built a general solution for alloca'd space.
> 

For stack coloring to work you would need to mark them with lifetime markers. 


> 
> On Mon, Nov 4, 2013 at 6:30 AM, Ali Javadi <aj14889 at yahoo.com> wrote:
> Hi,
> 
> In my llvm code I want to create some function calls. The function prototype is as follows: 
>   
> int memoize ( char *function_name, 
>                		int *int_params, unsigned num_ints,
> 	               double *double_params, unsigned num_doubles)
> 
> In order to create these calls I do the following for example:
> 
>   %88 = alloca [7 x i8]
>   store volatile [7 x i8] c"ORACLE\00", [7 x i8]* %88
>   %89 = getelementptr [7 x i8]* %88, i32 0, i32 0
>   
>   %90 = alloca [1 x i32]
>   %91 = getelementptr inbounds [1 x i32]* %90, i32 0, i32 0
>   store volatile i32 3, i32* %91
>   %92 = getelementptr inbounds [1 x i32]* %90, i32 0, i32 0
>   
>   %93 = alloca [0 x double]
>   %94 = getelementptr inbounds [0 x double]* %93, i32 0, i32 0
> 
>   %95 = call i32 @memoize(i8* %89, i32* %92, i32 1, double* %94, i32 0)
> 
> This works, but I need to create *many* such function calls in one "parent" function, and eventually all the "alloca" instructions add up to overflowing the stack. So I have two questions:
> 
> a) Is it possible to create the arrays for my function call args without using the alloca instruction (maybe use heap)?
> b) If not, can I release those alloca'd spaces during the function execution and not after it returns?
> 
> Thanks,
> Ali
> 
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