1 files changed, 13 insertions, 3 deletions
diff --git a/llvm/lib/Transforms/IPO/SCCP.cpp b/llvm/lib/Transforms/IPO/SCCP.cpp
index d50de34dfa48..2ecadd529170 100644
--- a/llvm/lib/Transforms/IPO/SCCP.cpp
+++ b/llvm/lib/Transforms/IPO/SCCP.cpp
@@ -169,6 +169,13 @@ static bool runIPSCCP(
   for (Function &F : M) {
     if (F.isDeclaration())
       continue;
+    // Skip the dead functions marked by FunctionSpecializer, avoiding removing
+    // blocks in dead functions. Set MadeChanges if there is any dead function
+    // that will be removed later.
+    if (IsFuncSpecEnabled && Specializer.isDeadFunction(&F)) {
+      MadeChanges = true;
+      continue;
+    }
 
     SmallVector<BasicBlock *, 512> BlocksToErase;
 
@@ -326,12 +333,15 @@ static bool runIPSCCP(
     LLVM_DEBUG(dbgs() << "Found that GV '" << GV->getName()
                       << "' is constant!\n");
     for (User *U : make_early_inc_range(GV->users())) {
-      // We can remove LoadInst here, because we already replaced its users
-      // with a constant.
+      // We can remove LoadInst here. The LoadInsts in dead functions marked by
+      // FuncSpec are not simplified to constants, thus poison them.
       assert((isa<StoreInst>(U) || isa<LoadInst>(U)) &&
              "Only Store|Load Instruction can be user of GlobalVariable at "
              "reaching here.");
-      cast<Instruction>(U)->eraseFromParent();
+      Instruction *I = cast<Instruction>(U);
+      if (isa<LoadInst>(I))
+        I->replaceAllUsesWith(PoisonValue::get(I->getType()));
+      I->eraseFromParent();
     }
 
     // Try to create a debug constant expression for the global variable