atomicCAS() does not change the value (when executed with LLVM)

[jwang323]

From max.m...@dameweb.de on May 11, 2013 17:04:28

What steps will reproduce the problem? 1. Run the following kernel, e.g. with 1 thread and 1 block:
global void atomicCASTest(unsigned int* x, unsigned int* ret){
unsigned int n = 2;
*x = n;
unsigned int x_old = atomicCAS(x, n, 5);
ret[0] = n;
ret[1] = x_old;
ret[2] = *x;
}

1. Check the results of array "ret". What is the expected output? What do you see instead? Expected output is ret[0]=2, ret[1]=2, ret[2]=5. This is the case when executed with emulator (configured in configure.ocelot).
   However when executed with llvm, the result is ret[0]=2, ret[1]=2, ret[2]=2, so atomicCAS() did not change the value of x. What version of the product are you using? On what operating system? Using llvm 3.2-6 and gpuocelot-svn built on 2013-05-01, on Arch Linux. Please provide any additional information below. Previously gpuocelot-svn on Arch Linux only compiled with llvm-svn. Therefore I patched the gpuocelot-svn build script to work with stable llvm version and to automatically download and build against LLVM header files. Maybe I made some mistake in the build script, so for reference here is the script: https://aur.archlinux.org/packages/gp/gpuocelot-svn/PKGBUILD

Original issue: http://code.google.com/p/gpuocelot/issues/detail?id=82

[jwang323]

From max.m...@dameweb.de on May 12, 2013 05:42:39

Now I have tried it with llvm-svn and llvm 3.1 (and for each a rebuild of gpuocelot) as well but the result was the same.
Maybe there is some error in gpuocelot when forwarding the atomic function to llvm?