[SYCL][USM] Fix USM malloc_shared and free to handle zero byte

sycl/source/detail/usm/usm_impl.cpp

@@ -27,6 +27,8 @@ namespace usm {
 void *alignedAllocHost(size_t Alignment, size_t Size, const context &Ctxt,
                        alloc Kind) {
   void *RetVal = nullptr;
+  if (Size == 0)
+    return nullptr;
   if (Ctxt.is_host()) {
     if (!Alignment) {
       // worst case default
@@ -72,6 +74,8 @@ void *alignedAllocHost(size_t Alignment, size_t Size, const context &Ctxt,
 void *alignedAlloc(size_t Alignment, size_t Size, const context &Ctxt,
                    const device &Dev, alloc Kind) {
   void *RetVal = nullptr;
+  if (Size == 0)
+    return nullptr;
   if (Ctxt.is_host()) {
     if (Kind == alloc::unknown) {
       RetVal = nullptr;
@@ -126,6 +130,8 @@ void *alignedAlloc(size_t Alignment, size_t Size, const context &Ctxt,
 }
 
 void free(void *Ptr, const context &Ctxt) {
+  if (Ptr == nullptr)
+    return;
   if (Ctxt.is_host()) {
     // need to use alignedFree here for Windows
     detail::OSUtil::alignedFree(Ptr);

sycl/test/regression/usm_malloc_shared.cpp

@@ -0,0 +1,49 @@
+// RUN: %clangxx -fsycl %s -o %t.out
+// RUN: env SYCL_DEVICE_TYPE=HOST %t.out
+// RUN: %CPU_RUN_PLACEHOLDER %t.out
+
+// This test checks if users will successfully allocate 160, 0, and -16 bytes of
+// shared memory, and also test user can call free() without worrying about
+// nullptr or invalid memory descriptor returned from malloc.
+
+#include <CL/sycl.hpp>
+#include <iostream>
+#include <stdlib.h>
+using namespace cl::sycl;
+
+int main(int argc, char *argv[]) {
+  auto exception_handler = [](cl::sycl::exception_list exceptions) {
+    for (std::exception_ptr const &e : exceptions) {
+      try {
+        std::rethrow_exception(e);
+      } catch (cl::sycl::exception const &e) {
+        std::cout << "Caught asynchronous SYCL "
+                     "exception:\n"
+                  << e.what() << std::endl;
+      }
+    }
+  };
+
+  queue myQueue(default_selector{}, exception_handler);
+  std::cout << "Device: " << myQueue.get_device().get_info<info::device::name>()
+            << std::endl;
+
+  double *ia = (double *)malloc_shared(160, myQueue);
+  double *ja = (double *)malloc_shared(0, myQueue);
+  double *result = (double *)malloc_shared(-16, myQueue);
+
+  assert(ia != nullptr);
+  assert(ja == nullptr);
+  assert(result == nullptr);
+
+  std::cout << "ia : " << ia << " ja: " << ja << " result : " << result
+            << std::endl;
+
+  // followings should not throw CL_INVALID_VALUE
+  cl::sycl::free(ia, myQueue);
+  cl::sycl::free(nullptr, myQueue);
+  cl::sycl::free(ja, myQueue);
+  cl::sycl::free(result, myQueue);
+
+  return 0;
+}