[LLVMdev] llvm-gcc loop unrolling

Evan Jones ejones at uwaterloo.ca
Wed Apr 20 06:41:07 PDT 2005

What component is responsible for loop unrolling, llvm-gcc, or some 
LLVM pass after GCC? When compiling this function:

void printArray( int array[16] ) {
	for( int i = 0; i < 16; ++ i ) {
		printf( "%d\n", array[i] );

llvm-gcc chooses to unroll this loop, and I don't think it should. It 
doesn't unroll the loop if there are 17 iterations, only 16. It also 
produces this output even when compiling with -Os, which is supposed to 
turn off optimizations like this.

Wouldn't it be better to leave the loop unrolling to some later 
optimization pass? This way, future passes can easily recognize that 
this is in fact a loop.

Evan Jones

More information about the llvm-dev mailing list