From b2c5ff3ed5c6a7436622d2670d7ee327a5b14f1c Mon Sep 17 00:00:00 2001
From: Bruno Cardoso Lopes <bruno.cardoso@gmail.com>
Date: Tue, 16 Apr 2024 18:26:59 -0700
Subject: [PATCH] [CIR][LLVMLowering] Fix handling of dense array conversions
 from const arrays

We were lacking handling of trailing zeros for constant arrays.
---
 .../lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp | 15 ++++++++++++++-
 clang/test/CIR/Lowering/const-array.cir           | 15 +++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/CIR/Lowering/const-array.cir

diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
index 1aeb03f90b61..5509534a0db3 100644
--- a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
+++ b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
@@ -1036,7 +1036,7 @@ template <> mlir::APFloat getZeroInitFromType(mlir::Type Ty) {
   llvm_unreachable("NYI");
 }
 
-// return the nested type and quiantity of elements for cir.array type.
+// return the nested type and quantity of elements for cir.array type.
 // e.g: for !cir.array<!cir.array<!s32i x 3> x 1>
 // it returns !s32i as return value and stores 3 to elemQuantity.
 mlir::Type getNestedTypeAndElemQuantity(mlir::Type Ty, unsigned &elemQuantity) {
@@ -1072,6 +1072,19 @@ void convertToDenseElementsAttrImpl(mlir::cir::ConstArrayAttr attr,
       llvm_unreachable("unknown element in ConstArrayAttr");
     }
   }
+
+  // Only fill in trailing zeros at the local cir.array level where the element
+  // type isn't another array (for the mult-dim case).
+  auto numTrailingZeros = attr.getTrailingZerosNum();
+  if (numTrailingZeros) {
+    auto localArrayTy = attr.getType().dyn_cast<mlir::cir::ArrayType>();
+    assert(localArrayTy && "expected !cir.array");
+
+    auto nestTy = localArrayTy.getEltType();
+    if (!nestTy.isa<mlir::cir::ArrayType>())
+      values.insert(values.end(), localArrayTy.getSize() - numTrailingZeros,
+                    getZeroInitFromType<StorageTy>(nestTy));
+  }
 }
 
 template <typename AttrTy, typename StorageTy>
diff --git a/clang/test/CIR/Lowering/const-array.cir b/clang/test/CIR/Lowering/const-array.cir
new file mode 100644
index 000000000000..7aff779a04fa
--- /dev/null
+++ b/clang/test/CIR/Lowering/const-array.cir
@@ -0,0 +1,15 @@
+// RUN: cir-translate %s -cir-to-llvmir -o -  | FileCheck %s -check-prefix=LLVM
+
+!u8i = !cir.int<u, 8>
+
+module {
+  cir.global "private" internal @normal_url_char = #cir.const_array<[#cir.int<0> : !u8i, #cir.int<1> : !u8i], trailing_zeros> : !cir.array<!u8i x 4>
+  // LLVM: @normal_url_char = internal global [4 x i8] c"\00\01\00\00"
+
+  cir.func @c0() -> !cir.ptr<!cir.array<!u8i x 4>> {
+    %0 = cir.get_global @normal_url_char : cir.ptr <!cir.array<!u8i x 4>>
+    cir.return %0 : !cir.ptr<!cir.array<!u8i x 4>>
+  }
+  // LLVM: define ptr @c0()
+  // LLVM: ret ptr @normal_url_char
+}