[fir] Add fir.string_lit conversion

[clementval]

Summary

This patch adds the conversion pattern for
the fir.string_lit operation.

This patch is part of the upstreaming effort from fir-dev branch.

Co-authored-by: Eric Schweitz <[e-mail]>
Co-authored-by: Jean Perier <[e-mail]>

[awarzynski]

LG, thanks!

flang/lib/Optimizer/CodeGen/CodeGen.cpp

477–496

[nit] else is not really required.

[clementval]

Rebase + remove useless else

flang/lib/Optimizer/CodeGen/CodeGen.cpp

matchAndRewrite(fir::BoxRankOp boxrank, OpAdaptor adaptor,
     auto loc = boxrank.getLoc();
     mlir::Type ty = convertType(boxrank.getType());
     auto result = getValueFromBox(loc, a, ty, rewriter, kRankPosInBox);
     rewriter.replaceOp(boxrank, result);
     return success();
   }
 };
 
+/// Lower `fir.string_lit` to LLVM IR dialect operation.
+struct StringLitOpConversion : public FIROpConversion<fir::StringLitOp> {
+  using FIROpConversion::FIROpConversion;
+
+  mlir::LogicalResult
+  matchAndRewrite(fir::StringLitOp constop, OpAdaptor adaptor,
+                  mlir::ConversionPatternRewriter &rewriter) const override {
+    auto ty = convertType(constop.getType());
+    auto attr = constop.getValue();
+    if (attr.isa<mlir::StringAttr>()) {
+      rewriter.replaceOpWithNewOp<mlir::LLVM::ConstantOp>(constop, ty, attr);
+      return success();
+    }
+
+    auto arr = attr.cast<mlir::ArrayAttr>();
+    auto charTy = constop.getType().cast<fir::CharacterType>();
+    unsigned bits = lowerTy().characterBitsize(charTy);
+    mlir::Type intTy = rewriter.getIntegerType(bits);
+    auto attrs = llvm::map_range(
+        arr.getValue(), [intTy, bits](mlir::Attribute attr) -> Attribute {
+          return mlir::IntegerAttr::get(
+              intTy,
+              attr.cast<mlir::IntegerAttr>().getValue().sextOrTrunc(bits));
+        });
+    mlir::Type vecType = mlir::VectorType::get(arr.size(), intTy);
+    auto denseAttr = mlir::DenseElementsAttr::get(
+        vecType.cast<mlir::ShapedType>(), llvm::to_vector<8>(attrs));
+    rewriter.replaceOpWithNewOp<mlir::arith::ConstantOp>(constop, ty,
+                                                         denseAttr);
+    return success();
+  }
+};
+
 // `fir.call` -> `llvm.call`
 struct CallOpConversion : public FIROpConversion<fir::CallOp> {
   using FIROpConversion::FIROpConversion;
 
   mlir::LogicalResult
   matchAndRewrite(fir::CallOp call, OpAdaptor adaptor,
                   mlir::ConversionPatternRewriter &rewriter) const override {
     SmallVector<mlir::Type> resultTys;
if (!forcedTargetTriple.empty()) {
       fir::setTargetTriple(mod, forcedTargetTriple);
     }
 
     auto *context = getModule().getContext();
     fir::LLVMTypeConverter typeConverter{getModule()};
     mlir::OwningRewritePatternList pattern(context);
     pattern.insert<
         AbsentOpConversion, AddcOpConversion, AddrOfOpConversion,
-        AllocaOpConversion, BoxAddrOpConversion, BoxCharLenOpConversion, BoxDimsOpConversion,
-        BoxEleSizeOpConversion, BoxIsAllocOpConversion, BoxIsArrayOpConversion,
-        BoxIsPtrOpConversion, BoxRankOpConversion, CallOpConversion,
-        CmpcOpConversion, ConvertOpConversion, DispatchOpConversion,
-        DispatchTableOpConversion, DTEntryOpConversion, DivcOpConversion,
-        EmboxCharOpConversion, ExtractValueOpConversion, HasValueOpConversion,
-        GenTypeDescOpConversion, GlobalLenOpConversion, GlobalOpConversion,
-        InsertOnRangeOpConversion, InsertValueOpConversion,
+        AllocaOpConversion, BoxAddrOpConversion, BoxCharLenOpConversion,
+        BoxDimsOpConversion, BoxEleSizeOpConversion, BoxIsAllocOpConversion,
+        BoxIsArrayOpConversion, BoxIsPtrOpConversion, BoxRankOpConversion,
+        CallOpConversion, CmpcOpConversion, ConvertOpConversion,
+        DispatchOpConversion, DispatchTableOpConversion, DTEntryOpConversion,
+        DivcOpConversion, EmboxCharOpConversion, ExtractValueOpConversion,
+        HasValueOpConversion, GenTypeDescOpConversion, GlobalLenOpConversion,
+        GlobalOpConversion, InsertOnRangeOpConversion, InsertValueOpConversion,
         IsPresentOpConversion, LoadOpConversion, NegcOpConversion,
         MulcOpConversion, SelectCaseOpConversion, SelectOpConversion,
         SelectRankOpConversion, SelectTypeOpConversion, StoreOpConversion,
-        SubcOpConversion, UnboxCharOpConversion, UndefOpConversion,
-        UnreachableOpConversion, ZeroOpConversion>(typeConverter);
+        StringLitOpConversion, SubcOpConversion, UnboxCharOpConversion,
+        UndefOpConversion, UnreachableOpConversion, ZeroOpConversion>(
+        typeConverter);
     mlir::populateStdToLLVMConversionPatterns(typeConverter, pattern);
     mlir::arith::populateArithmeticToLLVMConversionPatterns(typeConverter,
                                                             pattern);
     mlir::ConversionTarget target{*context};
     target.addLegalDialect<mlir::LLVM::LLVMDialect>();
 
     // required NOPs for applying a full conversion
     target.addLegalOp<mlir::ModuleOp>();

flang/test/Fir/convert-to-llvm.fir

func @absent() -> i1 {
   return %1 : i1
 }
 
 // CHECK-LABEL: @absent
 // CHECK-SAME:  () -> i1
 // CHECK-NEXT:  %[[ptr:.*]] = llvm.mlir.null : !llvm.ptr<i64>
 // CHECK-NEXT:  %[[ret_val:.*]] = llvm.call @is_present(%[[ptr]]) : (!llvm.ptr<i64>) -> i1
 // CHECK-NEXT:  llvm.return %[[ret_val]] : i1
+
+// -----
+
+// Test `fir.string_lit` conversion.
+
+func @string_lit0() {
+  %1 = fir.string_lit "Hello, World!"(13) : !fir.char<1>
+  return
+}
+
+// CHECK-LABEL: llvm.func @string_lit0
+// CHECK: %{{.*}} = llvm.mlir.constant("Hello, World!") : !llvm.array<13 x i8>
+
+func @string_lit1() {
+  %2 = fir.string_lit [158, 2345](2) : !fir.char<2>
+  return
+}
+
+// CHECK-LABEL: llvm.func @string_lit1
+// %{{.*}} = llvm.mlir.constant(dense<[158, 2345]> : vector<2xi16>) : !llvm.array<2 x i16>