CUDA: Check PTX version on host side to guard PDL dispatch (#23530)

* CUDA: Check PTX version on host side to guard PDL dispatch

Checking on `__CUDA_ARCH_LIST__` alone is insufficient for JIT, as this
variable doesn't differentiate between compiling for say sm_90, sm_90a
or sm_90f (so forward-jittable PTX vs. arch/family-specific PTX).

Thus, one can have a bug when compiling with
`DCMAKE_CUDA_ARCHITECTURES="89;90a"`, where current code would wrongly
dispatch to PDL on sm_90/sm_120 in forward-JIT mode.

This PR fixes this issue by checking `cudaFuncAttributes::ptxVersion` of
the incoming kernel at runtime. A check on ptxVersion alone is
sufficient, as device-codes will always be >= ptxVersion (and any
violation of this would be a severe bug in CUDA/nvcc), see:
 https://docs.nvidia.com/cuda/cuda-compiler-driver-nvcc/#gpu-code-code-code

* Implement MurmurHash3 mixer for better hash distribution

Magic constants were taken from boost:
2698b43803/include/boost/container_hash/detail/hash_mix.hpp (L19-L65)

* Update ggml/src/ggml-cuda/common.cuh

Co-authored-by: Johannes Gäßler <johannesg@5d6.de>

* Address review comments, make seed non-zero

* Apply code-formatting

* Replace std::size_t -> size_t for consistency

---------

Co-authored-by: Johannes Gäßler <johannesg@5d6.de>

ggml/src/ggml-cuda/common.cuh

@@ -7,6 +7,7 @@
 #include <cstdint>
 #include <cstdlib>
 #include <memory>
+#include <mutex>
 
 #if defined(GGML_USE_HIP)
 #define GGML_COMMON_DECL_HIP
@@ -1552,6 +1553,62 @@ struct ggml_cuda_pdl_config {
     ggml_cuda_pdl_config& operator=(ggml_cuda_pdl_config&&) = delete;
 
 };
+
+static bool ggml_cuda_kernel_can_use_pdl(const void * kernel) {
+    const int device = ggml_cuda_get_device();
+
+    struct cache_key {
+        int          device;
+        const void * kernel;
+
+        bool operator==(const cache_key & other) const { return device == other.device && kernel == other.kernel; }
+    };
+
+    struct cache_key_hash {
+        // MurmurHash3 mixing function for better hash distribution (vs. just std::hash which in some implementations simply returns the identity)
+        static size_t hash_mix(size_t x) {
+            std::uint64_t       y = x;
+            const std::uint64_t m = 0xe9846af9b1a615d;
+
+            y ^= y >> 32;
+            y *= m;
+            y ^= y >> 32;
+            y *= m;
+            y ^= y >> 28;
+
+            return static_cast<size_t>(y);
+        }
+
+        size_t operator()(const cache_key & key) const {
+            // Use a nonzero seed to avoid mapping all-zero keys to zero
+            size_t h = 42;
+            h        = hash_mix(h + key.device);
+            h        = hash_mix(h + reinterpret_cast<size_t>(key.kernel));
+            return h;
+        }
+    };
+
+    static std::mutex                                          cache_mutex;
+    static std::unordered_map<cache_key, bool, cache_key_hash> cache;
+
+    const cache_key             key = { device, kernel };
+    std::lock_guard<std::mutex> lock(cache_mutex);
+    const auto                  it = cache.find(key);
+    if (it != cache.end()) {
+        return it->second;
+    }
+
+    cudaFuncAttributes attr = {};
+    CUDA_CHECK(cudaFuncGetAttributes(&attr, kernel));
+
+    // PDL device-side primitives are emitted only for PTX versions >= 90.
+    // We have to guard on a loaded kernel's PTX version so a kernel forward-JIT'ed
+    // from pre-Hopper PTX to a Hopper-or-newer GPU does not opt into PDL.
+    const bool can_use_pdl = attr.ptxVersion >= 90;
+    cache.emplace(key, can_use_pdl);
+    return can_use_pdl;
+}
+
 #endif //defined(GGML_CUDA_USE_PDL)
 
 
@@ -1564,8 +1621,7 @@ static __inline__ void ggml_cuda_kernel_launch(Kernel kernel, const ggml_cuda_ke
         return env == nullptr || std::atoi(env) != 0;
     }();
 
-    const int cc = ggml_cuda_info().devices[ggml_cuda_get_device()].cc;
-    if (env_pdl_enabled && ggml_cuda_highest_compiled_arch(cc) >= GGML_CUDA_CC_HOPPER) {
+    if (env_pdl_enabled && ggml_cuda_kernel_can_use_pdl(reinterpret_cast<const void *>(kernel))) {
         auto pdl_cfg = ggml_cuda_pdl_config(launch_params);
 
         CUDA_CHECK(cudaLaunchKernelEx(&pdl_cfg.cfg, kernel, std::forward<Args>(args)... ));