[LLVMdev] Wrong behavior modifying and executing llvm::Function with JIT Engine
Adrian Ortega
elfus0.1 at gmail.com
Sun Jun 29 07:00:55 PDT 2014
I tried using 'getPointerToFunction()' and the correct function I
generated was called from C code, but when it runs inside the JIT engine
it always returns the value of the first function. I even tried to
'deleteBody()' and 'removeFromParent()' from the first function
generated, and still returns the first value.
I also tried using 'dump()' to see if the values where being updated.
This is the C code I run with the JIT engine:
#include <stdio.h>
int sum(int a, int b); // declaration
int get_int(int a, int b)
{
int x = sum(a,b);
printf("The result was: %d\n",x);
return x;
}
As you can see I print the return value of the function. The functions I
generate and that I called 'get_int_*()' in the previous email are now
called 'sum_mockup_N()'. This is the code LLVM IR code:
; Function Attrs: nounwind uwtable
define i32 @get_int(i32 %a, i32 %b) #0 {
entry:
%a.addr = alloca i32, align 4
%b.addr = alloca i32, align 4
%x = alloca i32, align 4
store i32 %a, i32* %a.addr, align 4
store i32 %b, i32* %b.addr, align 4
%0 = load i32* %a.addr, align 4
%1 = load i32* %b.addr, align 4
*%call = call i32 @sum_mockup(i32 %0, i32 %1)* *; Use the first
function generated*
store i32 %call, i32* %x, align 4
%2 = load i32* %x, align 4
%call1 = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds
([20 x i8]* @.str, i32 0, i32 0), i32 %2)
%3 = load i32* %x, align 4
ret i32 %3
}
The result was: 10
; sum always remains a declaration
declare i32 @sum(i32, i32) #1
*define i32 @sum_mockup(i32, i32)* *#1 {**
**mockup_block:**
** ret i32 10**
**}*
****************************
*[C Code] getPointerToFunction()= 10****// Pointer to*
*@sum_mockup(i32, i32)*
****************************
; Function Attrs: nounwind uwtable
define i32 @get_int(i32 %a, i32 %b) #0 {
entry:
%a.addr = alloca i32, align 4
%b.addr = alloca i32, align 4
%x = alloca i32, align 4
store i32 %a, i32* %a.addr, align 4
store i32 %b, i32* %b.addr, align 4
%0 = load i32* %a.addr, align 4
%1 = load i32* %b.addr, align 4
*%call = call i32 @sum(i32 %0, i32 %1)* *// Change it back to the
declaration*
store i32 %call, i32* %x, align 4
%2 = load i32* %x, align 4
%call1 = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds
([20 x i8]* @.str, i32 0, i32 0), i32 %2)
%3 = load i32* %x, align 4
ret i32 %3
}
; Function Attrs: nounwind uwtable
define i32 @get_int(i32 %a, i32 %b) #0 {
entry:
%a.addr = alloca i32, align 4
%b.addr = alloca i32, align 4
%x = alloca i32, align 4
store i32 %a, i32* %a.addr, align 4
store i32 %b, i32* %b.addr, align 4
%0 = load i32* %a.addr, align 4
%1 = load i32* %b.addr, align 4
*%call = call i32 @sum_mockup_1(i32 %0, i32 %1) ; Use the other
function generated*
store i32 %call, i32* %x, align 4
%2 = load i32* %x, align 4
%call1 = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds
([20 x i8]* @.str, i32 0, i32 0), i32 %2)
%3 = load i32* %x, align 4
ret i32 %3
}
The result was: 10
declare i32 @sum(i32, i32) #1
*define i32 @sum_mockup_1(i32, i32) #1 {**
**mockup_block:**
** ret i32 5**
**}*
****************************
*[C Code] getPointerToFunction()= 5* *// Pointer to*
*@sum_mockup_1(i32, i32)*
****************************
; Function Attrs: nounwind uwtable
define i32 @get_int(i32 %a, i32 %b) #0 {
entry:
%a.addr = alloca i32, align 4
%b.addr = alloca i32, align 4
%x = alloca i32, align 4
store i32 %a, i32* %a.addr, align 4
store i32 %b, i32* %b.addr, align 4
%0 = load i32* %a.addr, align 4
%1 = load i32* %b.addr, align 4
*%call = call i32 @sum(i32 %0, i32 %1)* *// Change it back to the
declaration*
store i32 %call, i32* %x, align 4
%2 = load i32* %x, align 4
%call1 = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds
([20 x i8]* @.str, i32 0, i32 0), i32 %2)
%3 = load i32* %x, align 4
ret i32 %3
}
If I get a pointer to the function 'get_int()' I still have the same
problem of getting the same return value of the first generated
function. But when I get a pointer to the generated functions themselves
'sum_mockup_*()' I get the actual value I'm expecting.
On 28/06/14 22:48, Yaron Keren wrote:
> getFunction() -> getPointerToFunction()
>
>
>
>
> 2014-06-29 6:40 GMT+03:00 Yaron Keren <yaron.keren at gmail.com
> <mailto:yaron.keren at gmail.com>>:
>
> Hi Adrian,
>
> freeMachineCodeForFunction is required but
> recompileAndLinkFunction is not,
> you can use getFunction() always.
>
> Try to M->dump() calling M->getFunction() where M is the Module *.
> See if how the changes appear in the module dump as expected.
>
> Yaron
>
>
>
>
>
> 2014-06-29 5:56 GMT+03:00 Adrian Ortega <elfus0.1 at gmail.com
> <mailto:elfus0.1 at gmail.com>>:
>
> Hello,
>
> The problem I'm having is that I modify a function body by
> using 'Value::replaceAllUsesWith' and then execute it with the
> JIT engine several times but I always get the output from the
> first iteration for all the iterations.
>
> This is what I do:
>
>
> I generate the following 2 functions on the fly based on the
> FunctionType of the declaration below in C code.
>
> define i32 @get_int_5(i32, i32) #1 {
> ret i32 5
> }
>
> define i32 @get_int_10(i32, i32) #1 {
> ret i32 10
> }
>
> I have the following C code:
>
>
> // This is only a declaration
> // I use this FunctionType to generate the functions above
> int sum(int a, int b);
>
> int get_int()
> {
> return sum(a,b);
> }
>
> I replace the call to 'sum()' by calling
> Value::replaceAllUsesWith for one of the functions generated
> above, run with JIT. I checked the code generated and it
> actually changes the call from 'sum()' to 'get_int_5()' and I
> get a 5 as return value when I call the function with the JIT
> execution engine.
>
> Then I repeat the previous step using
> 'Value::replaceAllUsesWith' for the next function I generated
> and run it with JIT. Then again the code generated is what I
> expected, this time
> function call changes from 'sum()' to 'get_int_10()', however
> the problem is I get a 5 instead of a 10.
>
> I tried 'recompileAndLinkFunction' as well as
> 'freeMachineCodeForFunction' and I always get the return value
> from the first function, and not the second as I should even
> though the generated code that I dump() says that it has the
> correct function call.
>
> I am using version 3.4 for both clang and llvm. And also I'm
> using the JIT Engine and not the MCJIT.
>
> Do you have have any idea why the references or 'uses' changes
> are not reflected in the code JIT'ed ?
>
> Regards.
>
>
>
>
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu <mailto:LLVMdev at cs.uiuc.edu>
> http://llvm.cs.uiuc.edu
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>
>
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