minimal diff showing kernel re-use

halide_opencl_cache_kernel.cc.diff

diff --git a/src/runtime/opencl.cpp b/src/runtime/opencl.cpp
index 3fb98b4..4b5eca2 100644
--- a/src/runtime/opencl.cpp
+++ b/src/runtime/opencl.cpp

+} // extern C
+
+#include <map>
+struct kernel_cache_t { bool cached; cl_kernel kernel; inline kernel_cache_t() : cached(false) {} };
+std::map<const char*, kernel_cache_t> precompiled_kernels;
+
+extern "C" {
+
 WEAK int halide_opencl_run(void *user_context,
                            void *state_ptr,
                            const char* entry_name,
@@ -924,7 +932,7 @@ WEAK int halide_opencl_run(void *user_context,
         << "shmem: " << shared_mem_bytes << "\n";
 
 
-    cl_int err;
+    cl_int err = CL_SUCCESS;
     ClContext ctx(user_context);
     if (ctx.error != CL_SUCCESS) {
         return ctx.error;
@@ -937,10 +945,19 @@ WEAK int halide_opencl_run(void *user_context,
     // Create kernel object for entry_name from the program for this module.
     halide_assert(user_context, state_ptr);
     cl_program program = ((module_state*)state_ptr)->program;
-
     halide_assert(user_context, program);
-    debug(user_context) << "    clCreateKernel " << entry_name << " -> ";
-    cl_kernel f = clCreateKernel(program, entry_name, &err);
+
+    kernel_cache_t& entry = precompiled_kernels[entry_name];
+    cl_kernel f;
+
+    if (!entry.cached) {
+        debug(user_context) << "    clCreateKernel " << entry_name << " -> ";
+        f = clCreateKernel(program, entry_name, &err);
+        entry.cached = true;
+        entry.kernel = f;
+    } else {
+        f = entry.kernel;
+    }
     if (err != CL_SUCCESS) {
         debug(user_context) << get_opencl_error_name(err) << "\n";
         error(user_context) << "CL: clCreateKernel " << entry_name << " failed: "
@@ -1055,9 +1072,9 @@ WEAK int halide_opencl_run(void *user_context,
         return err;
     }
 
-    debug(user_context) << "    Releasing kernel " << (void *)f << "\n";
-    clReleaseKernel(f);
-    debug(user_context) << "    clReleaseKernel finished" << (void *)f << "\n";
+    //debug(user_context) << "    Releasing kernel " << (void *)f << "\n";
+    //clReleaseKernel(f);
+    //debug(user_context) << "    clReleaseKernel finished" << (void *)f << "\n";