[CIR] Support wide string literals in CIR codegen (#171541)

This PR migrates support for wide string literals from the incubator to
upstream.

## Changes

- Implement wide string literal support in
`getConstantArrayFromStringLiteral`
- Handle wchar_t, char16_t, and char32_t string literals
- Collect code units and create constant arrays with IntAttr elements
- Use ZeroAttr for null-filled strings

## Testing

- Copied `wide-string.cpp` test file from incubator
- Expanded test to include wchar_t test cases (incubator only had
char16_t and char32_t)
- All tests pass

---------

Co-authored-by: Andy Kaylor <akaylor@nvidia.com>

Author: adams381

clang/lib/CIR/CodeGen/CIRGenModule.cpp

@@ -21,7 +21,9 @@
 #include "clang/AST/GlobalDecl.h"
 #include "clang/AST/RecordLayout.h"
 #include "clang/Basic/SourceManager.h"
+#include "clang/CIR/Dialect/IR/CIRAttrs.h"
 #include "clang/CIR/Dialect/IR/CIRDialect.h"
+#include "clang/CIR/Dialect/IR/CIRTypes.h"
 #include "clang/CIR/Interfaces/CIROpInterfaces.h"
 #include "clang/CIR/MissingFeatures.h"
 
@@ -31,6 +33,8 @@
 #include "mlir/IR/MLIRContext.h"
 #include "mlir/IR/Verifier.h"
 
+#include <algorithm>
+
 using namespace clang;
 using namespace clang::CIRGen;
 
@@ -962,9 +966,39 @@ CIRGenModule::getConstantArrayFromStringLiteral(const StringLiteral *e) {
     return builder.getString(str, eltTy, finalSize);
   }
 
-  errorNYI(e->getSourceRange(),
-           "getConstantArrayFromStringLiteral: wide characters");
-  return mlir::Attribute();
+  auto arrayTy = mlir::cast<cir::ArrayType>(convertType(e->getType()));
+
+  auto arrayEltTy = mlir::cast<cir::IntType>(arrayTy.getElementType());
+
+  uint64_t arraySize = arrayTy.getSize();
+  unsigned literalSize = e->getLength();
+  assert(arraySize == literalSize + 1 &&
+         "wide string literal array size must be literal length plus null "
+         "terminator");
+
+  // Check if the string is all null bytes before building the vector.
+  // In most non-zero cases, this will break out on the first element.
+  bool isAllZero = true;
+  for (unsigned i = 0; i < literalSize; ++i) {
+    if (e->getCodeUnit(i) != 0) {
+      isAllZero = false;
+      break;
+    }
+  }
+
+  if (isAllZero)
+    return cir::ZeroAttr::get(arrayTy);
+
+  // Otherwise emit a constant array holding the characters.
+  SmallVector<mlir::Attribute> elements;
+  elements.reserve(arraySize);
+  for (unsigned i = 0; i < literalSize; ++i)
+    elements.push_back(cir::IntAttr::get(arrayEltTy, e->getCodeUnit(i)));
+  // Add null terminator
+  elements.push_back(cir::IntAttr::get(arrayEltTy, 0));
+
+  auto elementsAttr = mlir::ArrayAttr::get(&getMLIRContext(), elements);
+  return builder.getConstArray(elementsAttr, arrayTy);
 }
 
 bool CIRGenModule::supportsCOMDAT() const {

clang/test/CIR/CodeGen/wide-string.cpp

@@ -0,0 +1,63 @@
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --check-prefix=CIR --input-file=%t.cir %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o %t-cir.ll
+// RUN: FileCheck --check-prefix=LLVM --input-file=%t-cir.ll %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o %t.ll
+// RUN: FileCheck --check-prefix=OGCG --input-file=%t.ll %s
+
+// Test with built-in char16_t type
+const char16_t *test_utf16() {
+  return u"你好世界";
+}
+
+// CIR: cir.global "private" constant cir_private dso_local @{{.+}} = #cir.const_array<[#cir.int<20320> : !u16i, #cir.int<22909> : !u16i, #cir.int<19990> : !u16i, #cir.int<30028> : !u16i, #cir.int<0> : !u16i]> : !cir.array<!u16i x 5>
+// LLVM: @{{.+}} = private constant [5 x i16] [i16 20320, i16 22909, i16 19990, i16 30028, i16 0]
+// OGCG: @{{.+}} = private unnamed_addr constant [5 x i16] [i16 20320, i16 22909, i16 19990, i16 30028, i16 0]
+
+const char32_t *test_utf32() {
+  return U"你好世界";
+}
+
+// CIR: cir.global "private" constant cir_private dso_local @{{.+}} = #cir.const_array<[#cir.int<20320> : !u32i, #cir.int<22909> : !u32i, #cir.int<19990> : !u32i, #cir.int<30028> : !u32i, #cir.int<0> : !u32i]> : !cir.array<!u32i x 5>
+// LLVM: @{{.+}} = private constant [5 x i32] [i32 20320, i32 22909, i32 19990, i32 30028, i32 0]
+// OGCG: @{{.+}} = private unnamed_addr constant [5 x i32] [i32 20320, i32 22909, i32 19990, i32 30028, i32 0]
+
+const char16_t *test_zero16() {
+  return u"\0\0\0\0";
+}
+
+// CIR: cir.global "private" constant cir_private dso_local @{{.+}} = #cir.zero : !cir.array<!u16i x 5>
+// LLVM: @{{.+}} = private constant [5 x i16] zeroinitializer
+// OGCG: @{{.+}} = private unnamed_addr constant [5 x i16] zeroinitializer
+
+const char32_t *test_zero32() {
+  return U"\0\0\0\0";
+}
+
+// CIR: cir.global "private" constant cir_private dso_local @{{.+}} = #cir.zero : !cir.array<!u32i x 5>
+// LLVM: @{{.+}} = private constant [5 x i32] zeroinitializer
+// OGCG: @{{.+}} = private unnamed_addr constant [5 x i32] zeroinitializer
+
+const wchar_t *test_wchar() {
+  return L"1234";
+}
+
+// CIR: cir.global "private" constant cir_private dso_local @{{.+}} = #cir.const_array<[#cir.int<49> : !s32i, #cir.int<50> : !s32i, #cir.int<51> : !s32i, #cir.int<52> : !s32i, #cir.int<0> : !s32i]> : !cir.array<!s32i x 5>
+// LLVM: @{{.+}} = private constant [5 x i32] [i32 49, i32 50, i32 51, i32 52, i32 0]
+// OGCG: @{{.+}} = private unnamed_addr constant [5 x i32] [i32 49, i32 50, i32 51, i32 52, i32 0]
+
+const wchar_t *test_wchar_zero() {
+  return L"";
+}
+
+// CIR: cir.global "private" constant cir_private dso_local @{{.+}} = #cir.zero : !cir.array<!s32i x 1>
+// LLVM: @{{.+}} = private constant [1 x i32] zeroinitializer
+// OGCG: @{{.+}} = private unnamed_addr constant [1 x i32] zeroinitializer
+
+const char16_t *test_char16_typedef() {
+  return u"test";
+}
+
+// CIR: cir.global "private" constant cir_private dso_local @{{.+}} = #cir.const_array<[#cir.int<116> : !u16i, #cir.int<101> : !u16i, #cir.int<115> : !u16i, #cir.int<116> : !u16i, #cir.int<0> : !u16i]> : !cir.array<!u16i x 5>
+// LLVM: @{{.+}} = private constant [5 x i16] [i16 116, i16 101, i16 115, i16 116, i16 0]
+// OGCG: @{{.+}} = private unnamed_addr constant [5 x i16] [i16 116, i16 101, i16 115, i16 116, i16 0]