[DirectX] This change fixes a circular reference discovered in flatten arrays

Author: farzonl

llvm/lib/Target/DirectX/DXILFlattenArrays.cpp

@@ -42,7 +42,7 @@ class DXILFlattenArraysLegacy : public ModulePass {
 
 struct GEPData {
   ArrayType *ParentArrayType;
-  Value *ParendOperand;
+  Value *ParentOperand;
   SmallVector<Value *> Indices;
   SmallVector<uint64_t> Dims;
   bool AllIndicesAreConstInt;
@@ -211,7 +211,7 @@ bool DXILFlattenArraysVisitor::visitAllocaInst(AllocaInst &AI) {
 
   ArrayType *FattenedArrayType = ArrayType::get(BaseType, TotalElements);
   AllocaInst *FlatAlloca =
-      Builder.CreateAlloca(FattenedArrayType, nullptr, AI.getName() + ".flat");
+      Builder.CreateAlloca(FattenedArrayType, nullptr, AI.getName() + ".1dim");
   FlatAlloca->setAlignment(AI.getAlign());
   AI.replaceAllUsesWith(FlatAlloca);
   AI.eraseFromParent();
@@ -222,6 +222,10 @@ void DXILFlattenArraysVisitor::recursivelyCollectGEPs(
     GetElementPtrInst &CurrGEP, ArrayType *FlattenedArrayType,
     Value *PtrOperand, unsigned &GEPChainUseCount, SmallVector<Value *> Indices,
     SmallVector<uint64_t> Dims, bool AllIndicesAreConstInt) {
+  // Check if this GEP is already in the map to avoid circular references
+  if (GEPChainMap.count(&CurrGEP) > 0)
+    return;
+
   Value *LastIndex = CurrGEP.getOperand(CurrGEP.getNumOperands() - 1);
   AllIndicesAreConstInt &= isa<ConstantInt>(LastIndex);
   Indices.push_back(LastIndex);
@@ -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);
 
   GEP.replaceAllUsesWith(FlatGEP);
   GEP.eraseFromParent();

llvm/test/CodeGen/DirectX/flatten-array.ll

@@ -123,7 +123,8 @@ define void @gep_4d_test ()  {
 @b = internal global [2 x [3 x [4 x i32]]] zeroinitializer, align 16
 
 define void @global_gep_load() {
-  ; CHECK: load i32, ptr getelementptr inbounds ([24 x i32], ptr @a.1dim, i32 0, i32 6), align 4
+  ; CHECK: [[GEP_PTR:%.*]] = getelementptr inbounds [24 x i32], ptr @a.1dim, i32 0, i32 6
+  ; CHECK-NEXT: load i32, ptr [[GEP_PTR]], align 4
   ; CHECK-NEXT:    ret void
   %1 = getelementptr inbounds [2 x [3 x [4 x i32]]], [2 x [3 x [4 x i32]]]* @a, i32 0, i32 0
   %2 = getelementptr inbounds [3 x [4 x i32]], [3 x [4 x i32]]* %1, i32 0, i32 1
@@ -176,7 +177,8 @@ define void @global_incomplete_gep_chain(i32 %row, i32 %col) {
 }
 
 define void @global_gep_store() {
-  ; CHECK: store i32 1, ptr getelementptr inbounds ([24 x i32], ptr @b.1dim, i32 0, i32 13), align 4
+  ; CHECK: [[GEP_PTR:%.*]] = getelementptr inbounds [24 x i32], ptr @b.1dim, i32 0, i32 13
+  ; CHECK-NEXT: store i32 1, ptr [[GEP_PTR]], align 4
   ; CHECK-NEXT:    ret void
   %1 = getelementptr inbounds [2 x [3 x [4 x i32]]], [2 x [3 x [4 x i32]]]* @b, i32 0, i32 1
   %2 = getelementptr inbounds [3 x [4 x i32]], [3 x [4 x i32]]* %1, i32 0, i32 0