[CFE] Add an internal option to use 'generic' as default address space for C/C++ LangOpts

clang/include/clang/Basic/LangOptions.def

@@ -261,6 +261,7 @@ LANGOPT(GPUDeferDiag, 1, 0, NotCompatible, "defer host/device related diagnostic
 LANGOPT(GPUExcludeWrongSideOverloads, 1, 0, NotCompatible, "always exclude wrong side overloads in overloading resolution for CUDA/HIP")
 LANGOPT(OffloadingNewDriver, 1, 0, NotCompatible, "use the new driver for generating offloading code.")
 LANGOPT(OffloadViaLLVM, 1, 0, NotCompatible, "target LLVM/Offload as portable offloading runtime.")
+LANGOPT(DefaultAddrSpaceIsGeneric, 1, 0, NotCompatible, "use generic address space as default address space for SPIR-V targets")
 
 LANGOPT(SYCLIsDevice      , 1, 0, NotCompatible, "Generate code for SYCL device")
 LANGOPT(SYCLIsHost        , 1, 0, NotCompatible, "SYCL host compilation")

clang/include/clang/Options/Options.td

@@ -9213,6 +9213,10 @@ def fdefault_calling_conv_EQ : Joined<["-"], "fdefault-calling-conv=">,
   NormalizedValuesScope<"LangOptions">,
   NormalizedValues<["DCC_CDecl", "DCC_FastCall", "DCC_StdCall", "DCC_VectorCall", "DCC_RegCall", "DCC_RtdCall"]>,
   MarshallingInfoEnum<LangOpts<"DefaultCallingConv">, "DCC_None">;
+def fdefault_addr_space_is_generic : Flag<["-"], "fdefault-addr-space-is-generic">,
+  HelpText<"Use generic address space as the default address space for SPIR-V targets">,
+  Visibility<[CC1Option]>,
+  MarshallingInfoFlag<LangOpts<"DefaultAddrSpaceIsGeneric">>;
 
 // These options cannot be marshalled, because they are used to set up the LangOptions defaults.
 def finclude_default_header : Flag<["-"], "finclude-default-header">,

clang/lib/Basic/Targets/SPIR.h

@@ -242,7 +242,8 @@ class LLVM_LIBRARY_VISIBILITY BaseSPIRTargetInfo : public TargetInfo {
         // AS as generic.
         (getTriple().isSPIRV() &&
          (Opts.CUDAIsDevice ||
-          getTriple().getVendor() == llvm::Triple::Intel)));
+          getTriple().getVendor() == llvm::Triple::Intel)) ||
+        Opts.DefaultAddrSpaceIsGeneric);
   }
 
   void setSupportedOpenCLOpts() override {

clang/test/CodeGen/default-as-generic-spirv64.c

@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -triple spirv64 -fdefault-addr-space-is-generic -emit-llvm -o - %s | FileCheck %s --check-prefix=GENERIC
+
+// Test that -fdefault-addr-space-is-generic causes unqualified pointers to be
+// in the generic address space (addrspace(4)) for spirv64 targets.
+
+void test_memcpy(void *dst, const void *src, unsigned long n) {
+  __builtin_memcpy(dst, src, n);
+}
+
+// GENERIC: define spir_func void @test_memcpy(ptr addrspace(4) noundef %dst, ptr addrspace(4) noundef %src, i64 noundef %n)
+// GENERIC: call void @llvm.memcpy.p4.p4.i64(ptr addrspace(4) align 1 %{{.*}}, ptr addrspace(4) align 1 %{{.*}}, i64 %{{.*}}, i1 false)
+
+void test_pointer(int *p) {
+  *p = 42;
+}
+
+// GENERIC: define spir_func void @test_pointer(ptr addrspace(4) noundef %p)