[flang-commits] [flang] [flang][fir] add codegen for fir.load of assumed-rank fir.box (PR #93569)

[Slava Zakharin via flang-commits]

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@@ -240,6 +240,32 @@ mlir::Value ConvertFIRToLLVMPattern::genBoxAttributeCheck(
                                              maskRes, c0);
 }
 
+mlir::Value ConvertFIRToLLVMPattern::computeBoxSize(
+    mlir::Location loc, TypePair boxTy, mlir::Value box,
+    mlir::ConversionPatternRewriter &rewriter) const {
+  auto firBoxType = mlir::dyn_cast<fir::BaseBoxType>(boxTy.fir);
+  assert(firBoxType && "must be a BaseBoxType");
+  const mlir::DataLayout &dl = lowerTy().getDataLayout();
+  if (!firBoxType.isAssumedRank())
+    return genConstantOffset(loc, rewriter, dl.getTypeSize(boxTy.llvm));
+  fir::BaseBoxType firScalarBoxType = firBoxType.getBoxTypeWithNewShape(0);
+  mlir::Type llvmScalarBoxType =
+      lowerTy().convertBoxTypeAsStruct(firScalarBoxType);
+  mlir::Value scalarBoxSize =
+      genConstantOffset(loc, rewriter, dl.getTypeSize(llvmScalarBoxType));
+  mlir::Value rawRank = getRankFromBox(loc, boxTy, box, rewriter);
+  mlir::Value rank =
+      integerCast(loc, rewriter, scalarBoxSize.getType(), rawRank);
+  mlir::Type llvmDimsType = getBoxEleTy(boxTy.llvm, {kDimsPosInBox, 1});
+  mlir::Value sizePerDim =
+      genConstantOffset(loc, rewriter, dl.getTypeSize(llvmDimsType));
+  mlir::Value dimsSize = rewriter.create<mlir::LLVM::MulOp>(
+      loc, sizePerDim.getType(), sizePerDim, rank);
+  mlir::Value size = rewriter.create<mlir::LLVM::AddOp>(
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vzakhari wrote:

I think here we assume that adding an array of `CFI_dim_t` into the middle of the descriptor structure does not introduce any padding.  It seems to be a correct assumption now, but can we verify it somehow?

I do not have any great suggestion, but maybe we can verify that sizes of LLVM types corresponding to `firBoxType.getBoxTypeWithNewShape(0)` and `firBoxType.getBoxTypeWithNewShape(1)` are different by exactly the `sizePerDim`.

https://github.com/llvm/llvm-project/pull/93569