[llvm] [DirectX] Reland #142853 with Circular GEP fixes (PR #143747)

[Finn Plummer via llvm-commits]

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@@ -271,10 +275,18 @@ bool DXILFlattenArraysVisitor::visitGetElementPtrInstInGEPChainBase(
         genInstructionFlattenIndices(GEPInfo.Indices, GEPInfo.Dims, Builder);
 
   ArrayType *FlattenedArrayType = GEPInfo.ParentArrayType;
-  Value *FlatGEP =
-      Builder.CreateGEP(FlattenedArrayType, GEPInfo.ParendOperand,
-                        {Builder.getInt32(0), FlatIndex},
-                        GEP.getName() + ".flat", GEP.getNoWrapFlags());
+
+  // Don't append '.flat' to an empty string. If the SSA name isn't available
+  // it could conflict with the ParentOperand's name.
+  std::string FlatName = GEP.hasName() ? GEP.getName().str() + ".flat" : "";
+
+  Value *FlatGEP = Builder.CreateGEP(FlattenedArrayType, GEPInfo.ParentOperand,
+                                     {Builder.getInt32(0), FlatIndex}, FlatName,
+                                     GEP.getNoWrapFlags());
+
+  // Store the new GEP in the map before replacing uses to avoid circular
+  // references
+  GEPChainMap.erase(&GEP);
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inbelic wrote:

I don't think I understand the comment here with the code correctly.

Is this intended to also insert `FlatGEP` to `GEPChainMap`?

https://github.com/llvm/llvm-project/pull/143747