[clang] [CIR] Pointer and vptr width from a CIR-native data-layout entry (PR #204185)

[Akshay K via cfe-commits]

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@@ -42,7 +43,29 @@ static void setMLIRDataLayout(mlir::ModuleOp &mod, const llvm::DataLayout &dl) {
   mlir::MLIRContext *mlirContext = mod.getContext();
   mlir::DataLayoutSpecInterface dlSpec =
       mlir::translateDataLayout(dl, mlirContext);
-  mod->setAttr(mlir::DLTIDialect::kDataLayoutAttrName, dlSpec);
+
+  // Add a CIR-native pointer data-layout entry so cir.ptr / cir.vptr size and
+  // alignment are driven by the data layout rather than hardcoded.
+  // The value stores {size-in-bits, abi-align-in-bits} keyed on cir.ptr.
+  //
+  // TODO(cir): Only the default address space is recorded and
+  // address-space-dependent pointer sizes are not modeled yet. Emit
+  // per-address-space entries.
+  assert(!cir::MissingFeatures::dataLayoutPtrHandlingBasedOnLangAS());
+  constexpr unsigned kBitsInByte = 8;
+  unsigned ptrSizeBits = dl.getPointerSizeInBits(/*AS=*/0);
+  unsigned ptrAlignBits =
+      dl.getPointerABIAlignment(/*AS=*/0).value() * kBitsInByte;
+  auto ptrKey = cir::PointerType::get(cir::VoidType::get(mlirContext));
+  auto ptrVal = mlir::DenseI32ArrayAttr::get(
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kumarak wrote:

Switch to using `SpecAttr` instead of a dense array.  

https://github.com/llvm/llvm-project/pull/204185