Revert "[IR] Copy comdats in GlobalObject::copyAttributesFrom" (D20631, rL270743)

[jlebar]

Summary

This breaks copyAttributesFrom when the destination lives in a different
module from the source. The decision in D21255 was to revert this patch
and handle comdat copying separately from copyAttributesFrom.

[rnk]

This patch should fix DAE:

diff --git a/lib/Transforms/IPO/DeadArgumentElimination.cpp b/lib/Transforms/IPO/DeadArgumentElimination.cpp
index d9da5e8..3caaa4a 100644
--- a/lib/Transforms/IPO/DeadArgumentElimination.cpp
+++ b/lib/Transforms/IPO/DeadArgumentElimination.cpp
@@ -147,6 +147,7 @@ bool DeadArgumentEliminationPass::DeleteDeadVarargs(Function &Fn) {
   // Create the new function body and insert it into the module...
   Function *NF = Function::Create(NFTy, Fn.getLinkage());
   NF->copyAttributesFrom(&Fn);
+  NF->setComdat(Fn.getComdat());
   Fn.getParent()->getFunctionList().insert(Fn.getIterator(), NF);
   NF->takeName(&Fn);

@@ -813,6 +814,7 @@ bool DeadArgumentEliminationPass::RemoveDeadStuffFromFunction(Function *F) {
   // Create the new function body and insert it into the module...
   Function *NF = Function::Create(NFTy, F->getLinkage());
   NF->copyAttributesFrom(F);
+  NF->setComdat(F->getComdat());
   NF->setAttributes(NewPAL);
   // Insert the new function before the old function, so we won't be processing
   // it again.

test/Transforms/DeadArgElim/comdat.ll

1 ↗

(On Diff #60889)

Please keep this test case and fix DAE

[jlebar]

Fix DAE.

[rnk]

lgtm

lib/IR/Globals.cpp

void GlobalObject::setGlobalObjectSubClassData(unsigned Val) {
   assert(getGlobalObjectSubClassData() == Val && "representation error");
 }
 
 void GlobalObject::copyAttributesFrom(const GlobalValue *Src) {
   GlobalValue::copyAttributesFrom(Src);
   if (const auto *GV = dyn_cast<GlobalObject>(Src)) {
     setAlignment(GV->getAlignment());
     setSection(GV->getSection());
-    setComdat(const_cast<GlobalObject *>(GV)->getComdat());
   }
 }
 
 std::string GlobalValue::getGlobalIdentifier(StringRef Name,
                                              GlobalValue::LinkageTypes Linkage,
                                              StringRef FileName) {
 
   // Value names may be prefixed with a binary '1' to indicate

lib/Linker/IRMover.cpp

GlobalValue *IRLinker::copyGlobalValueProto(const GlobalValue *SGV,
 
   if (ForDefinition)
     NewGV->setLinkage(SGV->getLinkage());
   else if (SGV->hasExternalWeakLinkage())
     NewGV->setLinkage(GlobalValue::ExternalWeakLinkage);
 
   NewGV->copyAttributesFrom(SGV);
 
-  // Don't copy the comdat, it's from the original module. We'll handle it
-  // later.
-  if (auto *NewGO = dyn_cast<GlobalObject>(NewGV))
-    NewGO->setComdat(nullptr);
-
   // Remove these copied constants in case this stays a declaration, since
   // they point to the source module. If the def is linked the values will
   // be mapped in during linkFunctionBody.
   if (auto *NewF = dyn_cast<Function>(NewGV)) {
     NewF->setPersonalityFn(nullptr);
     NewF->setPrefixData(nullptr);
     NewF->setPrologueData(nullptr);
   }

lib/Transforms/IPO/DeadArgumentElimination.cpp

bool DeadArgumentEliminationPass::DeleteDeadVarargs(Function &Fn) {
   std::vector<Type*> Params(FTy->param_begin(), FTy->param_end());
   FunctionType *NFTy = FunctionType::get(FTy->getReturnType(),
                                                 Params, false);
   unsigned NumArgs = Params.size();
 
   // Create the new function body and insert it into the module...
   Function *NF = Function::Create(NFTy, Fn.getLinkage());
   NF->copyAttributesFrom(&Fn);
+  NF->setComdat(Fn.getComdat());
   Fn.getParent()->getFunctionList().insert(Fn.getIterator(), NF);
   NF->takeName(&Fn);
 
   // Loop over all of the callers of the function, transforming the call sites
   // to pass in a smaller number of arguments into the new function.
   //
   std::vector<Value*> Args;
   for (Value::user_iterator I = Fn.user_begin(), E = Fn.user_end(); I != E; ) {
bool DeadArgumentEliminationPass::RemoveDeadStuffFromFunction(Function *F) {
 
   // No change?
   if (NFTy == FTy)
     return false;
 
   // Create the new function body and insert it into the module...
   Function *NF = Function::Create(NFTy, F->getLinkage());
   NF->copyAttributesFrom(F);
+  NF->setComdat(F->getComdat());
   NF->setAttributes(NewPAL);
   // Insert the new function before the old function, so we won't be processing
   // it again.
   F->getParent()->getFunctionList().insert(F->getIterator(), NF);
   NF->takeName(F);
 
   // Loop over all of the callers of the function, transforming the call sites
   // to pass in a smaller number of arguments into the new function.