[PATCH] D73310: Allow Module name to be used to generate a unique Module ID

[Sriraman Tallam via Phabricator via llvm-commits]

tmsriram created this revision.
tmsriram added reviewers: rnk, pcc, mehdi_amini.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

Modify getUniqueModuleID to use Module name for better uniqueness guarantees.

Module ID helps when there are no globals exported or when multiple definitions/ of the same globals are allowed in different modules (with "-z muldefs").  While it is highly likely that Module identifier is unique, it is not guaranteed.


https://reviews.llvm.org/D73310

Files:
  llvm/include/llvm/Transforms/Utils/ModuleUtils.h
  llvm/lib/Transforms/Utils/ModuleUtils.cpp


Index: llvm/lib/Transforms/Utils/ModuleUtils.cpp
===================================================================
--- llvm/lib/Transforms/Utils/ModuleUtils.cpp
+++ llvm/lib/Transforms/Utils/ModuleUtils.cpp
@@ -252,7 +252,7 @@
   });
 }
 
-std::string llvm::getUniqueModuleId(Module *M) {
+std::string llvm::getUniqueModuleId(Module *M, bool UseModuleId) {
   MD5 Md5;
   bool ExportsSymbols = false;
   auto AddGlobal = [&](GlobalValue &GV) {
@@ -273,8 +273,18 @@
   for (auto &IF : M->ifuncs())
     AddGlobal(IF);
 
-  if (!ExportsSymbols)
-    return "";
+  // When UseModuleId is true, we include the module identifier also.  Module
+  // ID helps when there are no globals exported or when multiple definitions
+  // of the same globals are allowed in different modules (with "-z muldefs").
+  // While it is highly likely that Module identifier is unique, it is not
+  // guaranteed.
+  if (UseModuleId && !M->getModuleIdentifier().empty()) {
+    Md5.update(M->getModuleIdentifier());
+    Md5.update(ArrayRef<uint8_t>{0});
+  } else {
+    if (!ExportsSymbols)
+      return "";
+  }
 
   MD5::MD5Result R;
   Md5.final(R);
Index: llvm/include/llvm/Transforms/Utils/ModuleUtils.h
===================================================================
--- llvm/include/llvm/Transforms/Utils/ModuleUtils.h
+++ llvm/include/llvm/Transforms/Utils/ModuleUtils.h
@@ -107,7 +107,10 @@
 /// If the module has no strong external symbols (such a module may still have a
 /// semantic effect if it performs global initialization), we cannot produce a
 /// unique identifier for this module, so we return the empty string.
-std::string getUniqueModuleId(Module *M);
+///
+/// If UseModuleId is true, we include the ModuleIdentifier string.  This is
+/// however not guaranteed to be unique.
+std::string getUniqueModuleId(Module *M, bool UseModuleId = false);
 
 class CallInst;
 namespace VFABI {


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