[llvm] [GlobalOpt] Refactor CleanupPointerRootUsers (PR #84694)

[Yingwei Zheng via llvm-commits]

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@@ -201,61 +201,51 @@ CleanupPointerRootUsers(GlobalVariable *GV,
 
   bool Changed = false;
 
-  // If Dead[n].first is the only use of a malloc result, we can delete its
-  // chain of computation and the store to the global in Dead[n].second.
-  SmallVector<std::pair<Instruction *, Instruction *>, 32> Dead;
-
+  // Collect all stores to GV.
+  SmallVector<Instruction *, 8> Writes;
   SmallVector<User *> Worklist(GV->users());
-  // Constants can't be pointers to dynamically allocated memory.
   while (!Worklist.empty()) {
     User *U = Worklist.pop_back_val();
-    if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
-      Value *V = SI->getValueOperand();
-      if (isa<Constant>(V)) {
-        Changed = true;
-        SI->eraseFromParent();
-      } else if (Instruction *I = dyn_cast<Instruction>(V)) {
-        if (I->hasOneUse())
-          Dead.push_back(std::make_pair(I, SI));
-      }
-    } else if (MemSetInst *MSI = dyn_cast<MemSetInst>(U)) {
-      if (isa<Constant>(MSI->getValue())) {
-        Changed = true;
-        MSI->eraseFromParent();
-      } else if (Instruction *I = dyn_cast<Instruction>(MSI->getValue())) {
-        if (I->hasOneUse())
-          Dead.push_back(std::make_pair(I, MSI));
-      }
-    } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(U)) {
-      GlobalVariable *MemSrc = dyn_cast<GlobalVariable>(MTI->getSource());
-      if (MemSrc && MemSrc->isConstant()) {
-        Changed = true;
-        MTI->eraseFromParent();
-      } else if (Instruction *I = dyn_cast<Instruction>(MTI->getSource())) {
-        if (I->hasOneUse())
-          Dead.push_back(std::make_pair(I, MTI));
-      }
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dtcxzyw wrote:

Why did you drop the support for memset/memcpy? It causes some regressions https://github.com/dtcxzyw/llvm-opt-benchmark/pull/466#discussion_r1546056742.

Please add some tests with memset/memcpy.


https://github.com/llvm/llvm-project/pull/84694