llvm dev - Jul 2011 - [LLVMdev] getting and setting array indices c interface

I really can't figure out how to get and set array indices from the c
interface. 

so to get an element I'm calling 

 tindex = *fn\SymbolTable(*index\name)
 index = LLVMBuildLoad(builder,tindex,"index")
 arr = *fn\SymbolTable(*array\name)
 arrptr = LLVMBuildLoad(Builder,arr,"arrayptr")
 tmp = LLVMBuildGEP(Builder,arrptr,index,0,"ptr")
 ptr = llvmBuildload(Builder,tmp,"ele")
 
and to set 
 
 tarr = *fn\SymbolTable(*array\name)
 Arr = LLVMBuildLoad(builder,tarr,"array")
 tval = *fn\SymbolTable(*value\name)
 val = LLVMBuildLoad(builder,tval,"val")
 tindex = *fn\SymbolTable(*index\name)
 index = LLVMBuildLoad(builder,tindex,"index")
 ptr = LLVMBuildGEP(builder,Arr,index,0,"ptr")
 LLVMBuildStore(builder,val,ptr) 

All seems to results in is getting and setting the first element


the output 

define i32 @Atest(i32 %a) {
Entry:
  %a1 = alloca i32
  store i32 %a, i32* %a1
  %ptrMyArray = alloca i32*
  %myArray = alloca i32, i32 25
  store i32* %myArray, i32** %ptrMyArray
  %x = alloca i32
  store i32 0, i32* %x
  br label %ForEntry1

ForEntry1:                                        ; preds = %Entry
  store i32 1, i32* %x
  br label %For1

For1:                                             ; preds = %ForBody1, %
ForEntry1
  %x2 = load i32* %x
  %cond = icmp sle i32 %x2, 25
  br i1 %cond, label %ForBody1, label %ForEnd1

ForBody1:                                         ; preds = %For1
  %array = load i32** %ptrMyArray
  %val = load i32* %x
  %index = load i32* %x
  %ptr = getelementptr i32* %array
  store i32 %val, i32* %ptr
  %ctr = load i32* %x
  %next = add i32 %ctr, 1
  store i32 %next, i32* %x
  br label %For1

ForEnd1:                                          ; preds = %For1
  %ind = load i32* %a1
  %array3 = load i32** %ptrMyArray
  %ptr = getelementptr i32* %array3
  %ele = load i32* %ptr
  ret i32 %ele
}

 


-- 
Andrew Ferguson
+649 372 6039
www.idlearts.com

On Fri, Jul 8, 2011 at 6:00 PM, Andrew Ferguson <andrewf at idlearts.com>
wrote:
> I really can't figure out how to get and set array indices from the c
> interface.
>
> so to get an element I'm calling
>
>  tindex = *fn\SymbolTable(*index\name)
>  index = LLVMBuildLoad(builder,tindex,"index")
>  arr = *fn\SymbolTable(*array\name)
>  arrptr = LLVMBuildLoad(Builder,arr,"arrayptr")
>  tmp = LLVMBuildGEP(Builder,arrptr,index,0,"ptr")
>  ptr = llvmBuildload(Builder,tmp,"ele")
>
> and to set
>
>  tarr = *fn\SymbolTable(*array\name)
>  Arr = LLVMBuildLoad(builder,tarr,"array")
>  tval = *fn\SymbolTable(*value\name)
>  val = LLVMBuildLoad(builder,tval,"val")
>  tindex = *fn\SymbolTable(*index\name)
>  index = LLVMBuildLoad(builder,tindex,"index")
>  ptr = LLVMBuildGEP(builder,Arr,index,0,"ptr")
>  LLVMBuildStore(builder,val,ptr)
>
> All seems to results in is getting and setting the first element
The signature of LLVMBuildGEP is the following:

LLVMValueRef LLVMBuildGEP(LLVMBuilderRef B, LLVMValueRef Pointer,
                          LLVMValueRef *Indices, unsigned NumIndices,
                          const char *Name);

If NumIndices is zero, you're ending up with a no-op GEP.  NumIndices
needs to be at least 1 to create a meaningful GEP.

-Eli