On 02/20/2014 07:29 PM, Cody Rigney wrote: > On Thu, Feb 20, 2014 at 4:14 AM, Andrew Haley <aph@xxxxxxxxxx> wrote: >> Hi, >> >> On 02/19/2014 07:04 PM, Cody Rigney wrote: >>> I'm trying to add NEON optimizations to OpenCV's LK optical flow. See >>> link below. >>> https://github.com/Itseez/opencv/blob/2.4/modules/video/src/lkpyramid.cpp >>> >>> The gcc version could vary since this is an open source project, but >>> the one I'm currently using is 4.8.1. The target architecture is ARMv7 >>> w/ NEON. The processor I'm testing on is an ARM >>> Cortex-A15(big.LITTLE). >>> >>> The problem is, in release mode (where optimizations are set) it does >>> not work properly. However, in debug mode, it works fine. I tracked >>> down a specific variable(FLT_SCALE) that was being optimized out and >>> made it volatile and that part worked fine after that. However, I'm >>> still having incorrect behavior from some other optimization. >> >> Forget about using volatile here. That's just wrong. >> >> You have to mark your inputs, outputs, and clobbers correctly. >> > That makes sense. In this case, the input parameters are actually > memory addresses. So how would I do an output or clobber that would > tell the compiler that the memory at those addresses will change? You can use a memory operand as an output, as in "=m"(*a) or simply add "memory" to the clobber list. And you must add all clobbered registers to the clobber list. Then it should work. Andrew.
