Use target's default CC if available; extend test.

Author: AlexVlx

clang/lib/Sema/SemaExprCXX.cpp

@@ -3499,12 +3499,17 @@ void Sema::DeclareGlobalAllocationFunction(DeclarationName Name,
   auto CreateAllocationFunctionDecl = [&](Attr *ExtraAttr) {
     // The MSVC STL has explicit cdecl on its (host-side) allocation function
     // specializations for the allocation, so in order to prevent a CC clash
-    // we set cdecl on the host-side implicit decls, knowing these do not get
-    // emitted when compiling for device.
+    // we use the host's CC, if available, or CC_C as a fallback, for the
+    // host-side implicit decls, knowing these do not get emitted when compiling
+    // for device.
     if (getLangOpts().CUDAIsDevice && ExtraAttr &&
         isa<CUDAHostAttr>(ExtraAttr) &&
-        Context.getTargetInfo().getTriple().isSPIRV())
-      EPI.ExtInfo = EPI.ExtInfo.withCallingConv(CallingConv::CC_C);
+        Context.getTargetInfo().getTriple().isSPIRV()) {
+      if (auto *ATI = Context.getAuxTargetInfo())
+        EPI.ExtInfo = EPI.ExtInfo.withCallingConv(ATI->getDefaultCallingConv());
+      else
+        EPI.ExtInfo = EPI.ExtInfo.withCallingConv(CallingConv::CC_C);
+    }
     QualType FnType = Context.getFunctionType(Return, Params, EPI);
     FunctionDecl *Alloc = FunctionDecl::Create(
         Context, GlobalCtx, SourceLocation(), SourceLocation(), Name, FnType,

clang/test/SemaHIP/amdgcnspirv-implicit-alloc-function-calling-conv.hip

@@ -1,6 +1,12 @@
 // RUN: %clang_cc1 %s -fcuda-is-device -std=c++17 -triple spirv32 -verify
 // RUN: %clang_cc1 %s -fcuda-is-device -std=c++17 -triple spirv64 -verify
 // RUN: %clang_cc1 %s -fcuda-is-device -std=c++17 -triple spirv64-amd-amdhsa -verify
+// RUN: %clang_cc1 %s -fcuda-is-device -std=c++17 -triple spirv32 -aux-triple x86_64-unknown-linux-gnu -verify
+// RUN: %clang_cc1 %s -fcuda-is-device -std=c++17 -triple spirv64 -aux-triple x86_64-unknown-linux-gnu -verify
+// RUN: %clang_cc1 %s -fcuda-is-device -std=c++17 -triple spirv64-amd-amdhsa -aux-triple x86_64-unknown-linux-gnu -verify
+// RUN: %clang_cc1 %s -fcuda-is-device -std=c++17 -triple spirv32 -aux-triple x86_64-pc-windows-msvc -verify
+// RUN: %clang_cc1 %s -fcuda-is-device -std=c++17 -triple spirv64 -aux-triple x86_64-pc-windows-msvc -verify
+// RUN: %clang_cc1 %s -fcuda-is-device -std=c++17 -triple spirv64-amd-amdhsa -aux-triple x86_64-pc-windows-msvc -verify
 
 // expected-no-diagnostics