[clang][cuda] Use the source filename for module ID

clang/lib/CodeGen/CGCUDANV.cpp

@@ -29,6 +29,7 @@
 #include "llvm/IR/ReplaceConstant.h"
 #include "llvm/ProfileData/InstrProf.h"
 #include "llvm/Support/Format.h"
+#include "llvm/Support/MD5.h"
 #include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/Transforms/Utils/ModuleUtils.h"
 
@@ -1041,12 +1042,19 @@ llvm::Function *CGNVCUDARuntime::makeModuleCtorFunction() {
     }
   } else {
     // Generate a unique module ID.
+    // Note that this is unique in a build (with some collision probability
+    // inherent to MD5 hashing) as long as each compilation sees modules with
+    // different `SourceFileName`s. Builds using absolute paths or paths
+    // relative to the same base path should be OK. This is similar to the
+    // guarantees for ThinLTO and GlobalValue's GUID.
+    // If desired, a stronger uniqueness guarantee could be computed (with a
+    // small refactoring) with `llvm::getUniqueModuleId`, which hashes the
+    // module content (and, therefore, a compile-time tradeoff).
     SmallString<64> ModuleID;
     llvm::raw_svector_ostream OS(ModuleID);
     OS << ModuleIDPrefix
        << llvm::format("%" PRIx64,
-                       llvm::GlobalValue::getGUIDAssumingExternalLinkage(
-                           FatbinWrapper->getName()));
+                       llvm::MD5Hash(TheModule.getSourceFileName()));
     llvm::Constant *ModuleIDConstant = makeConstantArray(
         std::string(ModuleID), "", ModuleIDSectionName, 32, /*AddNull=*/true);
 

clang/test/CodeGenCUDA/device-stub.cu

@@ -64,6 +64,19 @@
 // RUN:     -o - -x hip\
 // RUN:   | FileCheck -allow-deprecated-dag-overlap %s --check-prefixes=ALL,WIN,HIP,HIPNEF
 
+// Verify that module IDs are distinct when the module source path is distinct.
+// RUN: rm -rf %t_distinct
+// RUN: mkdir -p %t_distinct
+// RUN: cp %s %t_distinct/filename1.cu
+// RUN: cp %s %t_distinct/filename2.cu
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm %t_distinct/filename1.cu -I%S \
+// RUN:     -target-sdk-version=8.0 -fgpu-rdc -fcuda-include-gpubinary %t \
+// RUN:     -o - | grep __nv_module_id &> %t_module_id_1
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm %t_distinct/filename2.cu -I%S \
+// RUN:     -target-sdk-version=8.0 -fgpu-rdc -fcuda-include-gpubinary %t \
+// RUN:     -o - | grep __nv_module_id &> %t_module_id_2
+// RUN: not diff %t_module_id_1 %t_module_id_2
+
 #include "Inputs/cuda.h"
 
 #ifndef NOGLOBALS