0c20483853
Using blend to do masked stores is unsafe if all of the lanes are off: it may read from or write to invalid memory. For now, this workaround transforms all 'if' statements into coherent 'if's, ensuring that an instruction only runs if at least on program instance wants to be running it. One nice thing about this change is that a number of implementations of various builtins can be simplified, since they no longer need to confirm that at least one program instance is running. It might be nice to re-enable regular if statements in a future checkin, but we'd want to make sure they don't have any masked loads or blended masked stores in their statement lists. There isn't a performance impact for any of the examples with this change, so it's unclear if this is important. Note that this only impacts 'if' statements with a varying condition.
============================== Intel(r) SPMD Program Compiler ============================== Welcome to the Intel(r) SPMD Program Compiler (ispc)! ispc is a new compiler for "single program, multiple data" (SPMD) programs. Under the SPMD model, the programmer writes a program that mostly appears to be a regular serial program, though the execution model is actually that a number of program instances execute in parallel on the hardware. ispc compiles a C-based SPMD programming language to run on the SIMD units of CPUs; it frequently provides a a 3x or more speedup on CPUs with 4-wide SSE units, without any of the difficulty of writing intrinsics code. ispc is an open source compiler under the BSD license; see the file LICENSE.txt. ispc supports Windows, Mac, and Linux, with both x86 and x86-64 targets. It currently supports the SSE2 and SSE4 instruction sets, though support for AVX should be available soon. For more information and examples, as well as a wiki and the bug database, see the ispc distribution site, http://ispc.github.com.