[llvm] [IPSCCP] Variable not visible at Og: (PR #66745)

[Felipe de Azevedo Piovezan via llvm-commits]

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@@ -371,6 +372,52 @@ static bool runIPSCCP(
       StoreInst *SI = cast<StoreInst>(GV->user_back());
       SI->eraseFromParent();
     }
+
+    // Try to create a debug constant expression for the glbal variable
+    // initializer value.
+    SmallVector<DIGlobalVariableExpression *, 1> GVEs;
+    GV->getDebugInfo(GVEs);
+    if (GVEs.size() == 1) {
+      DIBuilder DIB(M);
+
+      // Create integer constant expression.
+      auto createIntExpression = [&DIB](const Constant *CV) -> DIExpression * {
+        const APInt &API = dyn_cast<ConstantInt>(CV)->getValue();
+        std::optional<uint64_t> InitIntOpt;
+        if (API.isNonNegative())
+          InitIntOpt = API.tryZExtValue();
+        else if (auto Temp = API.trySExtValue(); Temp.has_value())
+          // Transform a signed optional to unsigned optional.
+          InitIntOpt = (uint64_t)Temp.value();
+        return DIB.createConstantValueExpression(InitIntOpt.value());
+      };
+
+      const Constant *CV = GV->getInitializer();
+      Type *Ty = GV->getValueType();
+      if (Ty->isIntegerTy()) {
+        GVEs[0]->replaceOperandWith(1, createIntExpression(CV));
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felipepiovezan wrote:

Are we allowed to mutate a metadata like this? IIUC we can only do this if it is uniqued? Or not uniqued? I can never remember exactly

https://github.com/llvm/llvm-project/pull/66745