[flang] fir.emboxchar codegen with static length fir.char types

[jeanPerier]

Summary

The verifier of fir.emboxchar accepts fir.char<kind, constant> types,
but its codegen failed because of a missing cast. It is convenient and
safe to not require making the cast in FIR, so add it in codegen.

[clementval]

LG

flang/lib/Optimizer/CodeGen/CodeGen.cpp

matchAndRewrite(fir::EmboxCharOp emboxChar, OpAdaptor adaptor,
     mlir::Location loc = emboxChar.getLoc();
     mlir::Type llvmStructTy = convertType(emboxChar.getType());
     auto llvmStruct = rewriter.create<mlir::LLVM::UndefOp>(loc, llvmStructTy);
 
     mlir::Type lenTy =
         llvmStructTy.cast<mlir::LLVM::LLVMStructType>().getBody()[1];
     mlir::Value lenAfterCast = integerCast(loc, rewriter, lenTy, charBufferLen);
 
+    mlir::Type addrTy =
+        llvmStructTy.cast<mlir::LLVM::LLVMStructType>().getBody()[0];
+    if (addrTy != charBuffer.getType())
+      charBuffer =
+          rewriter.create<mlir::LLVM::BitcastOp>(loc, addrTy, charBuffer);
+
     auto insertBufferOp = rewriter.create<mlir::LLVM::InsertValueOp>(
         loc, llvmStruct, charBuffer, 0);
     rewriter.replaceOpWithNewOp<mlir::LLVM::InsertValueOp>(
         emboxChar, insertBufferOp, lenAfterCast, 1);
 
     return mlir::success();
   }
 };

flang/test/Fir/boxchar.fir

func.func @get_name() {
   %2 = arith.constant 9 : i64
   %3 = fir.convert %1 : (!fir.ref<!fir.char<1,9>>) -> !fir.ref<!fir.char<1,?>>
   %4 = fir.emboxchar %3, %2 : (!fir.ref<!fir.char<1,?>>, i64) -> !fir.boxchar<1>
   // CHECK: call void @callee(ptr @name, i64 9)
   fir.call @callee(%4) : (!fir.boxchar<1>) -> ()
   return
 }
 
+// CHECK-LABEL: define void @get_name_2
+func.func @get_name_2() {
+  %1 = fir.address_of (@name) : !fir.ref<!fir.char<1,9>>
+  %2 = arith.constant 9 : i64
+  %4 = fir.emboxchar %1, %2 : (!fir.ref<!fir.char<1,9>>, i64) -> !fir.boxchar<1>
+  // CHECK: call void @callee(ptr @name, i64 9)
+  fir.call @callee(%4) : (!fir.boxchar<1>) -> ()
+  return
+}
+
 fir.global @name constant : !fir.char<1,9> {
   %str = fir.string_lit "Your name"(9) : !fir.char<1,9>
   //constant 1
   fir.has_value %str : !fir.char<1,9>
 }