[SYCL] Add DPC++ RT support for SYCL2020 spec constants' default values (#3667)

This patch introduces the support of default values for SYCL2020
specialization constants in DPC++ runtime.

Co-authored-by: Alexander Batashev <[email protected]>

Author: dm-vodopyanov

sycl/include/CL/sycl/detail/pi.h

@@ -673,6 +673,10 @@ static const uint8_t PI_DEVICE_BINARY_OFFLOAD_KIND_SYCL = 4;
 /// PropertySetRegistry::SYCL_SPECIALIZATION_CONSTANTS defined in
 /// PropertySetIO.h
 #define __SYCL_PI_PROPERTY_SET_SPEC_CONST_MAP "SYCL/specialization constants"
+/// PropertySetRegistry::SYCL_SPEC_CONSTANTS_DEFAULT_VALUES defined in
+/// PropertySetIO.h
+#define __SYCL_PI_PROPERTY_SET_SPEC_CONST_DEFAULT_VALUES_MAP                   \
+  "SYCL/specialization constants default values"
 /// PropertySetRegistry::SYCL_DEVICELIB_REQ_MASK defined in PropertySetIO.h
 #define __SYCL_PI_PROPERTY_SET_DEVICELIB_REQ_MASK "SYCL/devicelib req mask"
 /// PropertySetRegistry::SYCL_KERNEL_PARAM_OPT_INFO defined in PropertySetIO.h

sycl/include/CL/sycl/detail/pi.hpp

@@ -318,6 +318,14 @@ class DeviceBinaryImage {
   /// like:
   /// { ID5, 0, 4 }
   const PropertyRange &getSpecConstants() const { return SpecConstIDMap; }
+  const PropertyRange getSpecConstantsDefaultValues() const {
+    // We can't have this variable as a class member, since it would break
+    // the ABI backwards compatibility.
+    DeviceBinaryImage::PropertyRange SpecConstDefaultValuesMap;
+    SpecConstDefaultValuesMap.init(
+        Bin, __SYCL_PI_PROPERTY_SET_SPEC_CONST_DEFAULT_VALUES_MAP);
+    return SpecConstDefaultValuesMap;
+  }
   const PropertyRange &getDeviceLibReqMask() const { return DeviceLibReqMask; }
   const PropertyRange &getKernelParamOptInfo() const {
     return KernelParamOptInfo;

sycl/source/detail/device_image_impl.hpp

@@ -218,6 +218,12 @@ class device_image_impl {
           MBinImage->getSpecConstants();
       using SCItTy = pi::DeviceBinaryImage::PropertyRange::ConstIterator;
 
+      // get default values for specialization constants
+      const pi::DeviceBinaryImage::PropertyRange &SCDefValRange =
+          MBinImage->getSpecConstantsDefaultValues();
+
+      bool HasDefaultValues = SCDefValRange.begin() != SCDefValRange.end();
+
       // This variable is used to calculate spec constant value offset in a
       // flat byte array.
       unsigned BlobOffset = 0;
@@ -250,12 +256,20 @@ class device_image_impl {
           // supposed to be called from c'tor.
           MSpecConstSymMap[std::string{SCName}].push_back(
               SpecConstDescT{/*ID*/ It[0], /*CompositeOffset*/ It[1],
-                             /*Size*/ It[2], BlobOffset});
+                             /*Size*/ It[2], BlobOffset, HasDefaultValues});
           BlobOffset += /*Size*/ It[2];
           It += NumElements;
         }
       }
       MSpecConstsBlob.resize(BlobOffset);
+
+      if (HasDefaultValues) {
+        pi::ByteArray DefValDescriptors =
+            pi::DeviceBinaryProperty(*SCDefValRange.begin()).asByteArray();
+        std::uninitialized_copy(&DefValDescriptors[8],
+                                &DefValDescriptors[8] + MSpecConstsBlob.size(),
+                                MSpecConstsBlob.data());
+      }
     }
   }
 

sycl/unittests/CMakeLists.txt

@@ -15,4 +15,5 @@ add_subdirectory(pi)
 add_subdirectory(kernel-and-program)
 add_subdirectory(queue)
 add_subdirectory(scheduler)
+add_subdirectory(spec_constants)
 add_subdirectory(thread_safety)