[llvm] [DirectX] Simplify and correct the flattening of GEPs in DXILFlattenArrays (PR #146173)

[Deric C. via llvm-commits]

================
@@ -40,18 +41,19 @@ class DXILFlattenArraysLegacy : public ModulePass {
   static char ID; // Pass identification.
 };
 
-struct GEPData {
-  ArrayType *ParentArrayType;
-  Value *ParentOperand;
-  SmallVector<Value *> Indices;
-  SmallVector<uint64_t> Dims;
-  bool AllIndicesAreConstInt;
+struct GEPInfo {
+  ArrayType *RootFlattenedArrayType;
+  Value *RootPointerOperand;
+  SmallMapVector<Value *, APInt, 4> VariableOffsets;
+  APInt ConstantOffset;
 };
 
 class DXILFlattenArraysVisitor
     : public InstVisitor<DXILFlattenArraysVisitor, bool> {
 public:
-  DXILFlattenArraysVisitor() {}
+  DXILFlattenArraysVisitor(
+      DenseMap<GlobalVariable *, GlobalVariable *> &GlobalMap)
----------------
Icohedron wrote:

It's necessary because otherwise the `DXILFlattenArraysVisitor` won't have visibility of the `GlobalMap` which comes from a stack-allocated variable here
https://github.com/llvm/llvm-project/blob/db9162dd3c12e9f5e1d28abdfedf9758fd575814/llvm/lib/Target/DirectX/DXILFlattenArrays.cpp#L462-L466

which is necessary to determine the type of the GEP
https://github.com/llvm/llvm-project/blob/db9162dd3c12e9f5e1d28abdfedf9758fd575814/llvm/lib/Target/DirectX/DXILFlattenArrays.cpp#L273-L284

https://github.com/llvm/llvm-project/pull/146173