[LLVMdev] Why int variable get promoted to i64

[Joe Abbey]

Because you are compiling for a 64-bit system which uses LP64.  As such pointers are 64-bit in length... while integers remain defined as 32-bits. 

So why 64-bits for i?  The compiler is treating index variables special.  Index variables need to be able to index 64-bits of space and in fact you'll see the promotion here:

for.body:                                         ; preds = %for.cond
  %tmp2 = load i32* %i                            ; <i32> [#uses=1]
  %tmp3 = load i32** %x.addr                      ; <i32*> [#uses=1]
  %idxprom = sext i32 %tmp2 to i64                ; <i64> [#uses=1]
  %arrayidx = getelementptr inbounds i32* %tmp3, i64 %idxprom ; <i32*> [#uses=1]

Cheers,

Joe

On Aug 19, 2011, at 5:32 AM, 陳韋任 wrote:

> int test(int x[], int y[], int n) {
>  int i = 0;
>  int sum = 0;
>  for ( ; i < n; i++) {
>    sum += x[i] * y[i];
>  }
>  return sum;
> }

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