[LLVMdev] question on constant folding

[Seung Jae Lee]

Hello, LLVMers.

I have a quick question for constant folding.
When I treated a code twice by changing the data type from 'floating point' to 'integer,'
What I found was:
optimization is done better for the code having int's.
E.g.,  for this simple code:
-------------------------------------------------------------
double foo() {

  double i,j;
  double sum = 0;
  for (i=0; i<100; i++) {
    sum +=  i;
    for (j=0; j<100; j++)
      sum += 2;
  }

  return sum;
}
-------------------------------------------------------------

$llvm-gcc -O4 -emit-llvm foo.c  -c -o foo.bc
$opt -std-compile-opts -reg2mem foo.bc -o foo_optimized.bc

gave me a really long LLVM IR code with many basic blocks..

However, when I just changed the types to 'long' as follows:
-------------------------------------------------------------
long foo() {

  long i,j;
  long sum = 0;
  for (i=0; i<100; i++)
  {
    sum +=  i;
    for (j=0; j<100; j++)
      sum += 2;
  }

  return sum;
}
-------------------------------------------------------------

This code simply gave me:
-------------------------------------------------------------
define i32 @foo() nounwind  {
        %"reg2mem alloca point" = bitcast i32 0 to i32          ; <i32> [#uses=0]
        ret i32 24950
}
-------------------------------------------------------------

Could you anybody tell me why interger type code shows the better performance in constant folding with LLVM?

Thank you in advance..
SJ