[SYCL] Fix get_specialization_constant segmentation fault (#8542)

In certain cases get_specialization_constant would cause a segmentation
fault, likely due to strict aliasing violations. This commit changes the
implementation to use memcpy of the data into the resulting object, as
this can be assumed to be valid due to specialization constants being
device-copyable.

---------

Signed-off-by: Larsen, Steffen <[email protected]>

Author: steffenlarsen

sycl/include/sycl/kernel_bundle.hpp

@@ -308,17 +308,19 @@ class kernel_bundle : public detail::kernel_bundle_plain,
   template <auto &SpecName>
   typename std::remove_reference_t<decltype(SpecName)>::value_type
   get_specialization_constant() const {
-    const char *SpecSymName = detail::get_spec_constant_symbolic_ID<SpecName>();
-    if (!is_specialization_constant_set(SpecSymName))
-      return SpecName.getDefaultValue();
-
     using SCType =
         typename std::remove_reference_t<decltype(SpecName)>::value_type;
 
+    const char *SpecSymName = detail::get_spec_constant_symbolic_ID<SpecName>();
+    SCType Res{SpecName.getDefaultValue()};
+    if (!is_specialization_constant_set(SpecSymName))
+      return Res;
+
     std::array<char, sizeof(SCType)> RetValue;
     get_specialization_constant_impl(SpecSymName, RetValue.data());
+    std::memcpy(&Res, RetValue.data(), sizeof(SCType));
 
-    return *reinterpret_cast<SCType *>(RetValue.data());
+    return Res;
   }
 
   /// \returns an iterator to the first device image kernel_bundle contains

sycl/unittests/kernel-and-program/Cache.cpp

@@ -68,7 +68,11 @@ template <> const char *get_spec_constant_symbolic_ID<SpecConst1>() {
 static sycl::unittest::PiImage generateDefaultImage() {
   using namespace sycl::unittest;
 
+  std::vector<char> SpecConstData;
+  PiProperty SC1 = makeSpecConstant<int>(SpecConstData, "SC1", {0}, {0}, {42});
+
   PiPropertySet PropSet;
+  addSpecConstants({SC1}, std::move(SpecConstData), PropSet);
 
   std::vector<unsigned char> Bin{0, 1, 2, 3, 4, 5}; // Random data
 
@@ -256,7 +260,7 @@ TEST_F(KernelAndProgramCacheTest, SpecConstantCacheNegative) {
   detail::KernelProgramCache::ProgramCache &Cache =
       CtxImpl->getKernelProgramCache().acquireCachedPrograms().get();
 
-  EXPECT_EQ(Cache.size(), 1U) << "Expect non-empty cache";
+  EXPECT_EQ(Cache.size(), 2U) << "Expect an entry for each build in the cache.";
 }
 
 // Check that kernel_bundle created through join() is not cached.