[CIR][CodeGen] Bitfield operations (#279)

As we discussed in #233, there is a desire to have CIR operations for
bit fields set/get access and do all the stuff in the `LoweringPrepare`.

There is one thing I want to discuss, that's why the PR is marked as a
draft now.
Looks like I have to introduce some redundant helpers for all these `or`
and `shift` operations: while we were in the `CodeGen` area, we used
`CIRGenBuilder` and we could easily extend it. I bet we don't want to
depend from `CodeGen` in the `LoweringPrepare`. Once it's true. what is
a good place for all this common things? As an idea, we could introduce
one more layer for builder, with no state involved - just helpers and
nothing else. But again, what is a good place for it from your point of
view?

Author: gitoleg

clang/include/clang/CIR/Dialect/IR/CIRAttrs.td

@@ -521,4 +521,31 @@ def GlobalCtorAttr : CIR_Attr<"GlobalCtor", "globalCtor"> {
   ];
   let skipDefaultBuilders = 1;
 }
+
+def BitfieldInfoAttr : CIR_Attr<"BitfieldInfo", "bitfield_info"> {
+  let summary = "Represents a bit field info";
+  let description = [{
+    Holds the next information about bitfields: name, storage type, a bitfield size
+    and position in the storage, if the bitfield is signed or not.
+  }];
+  let parameters = (ins "StringAttr":$name,
+                        "Type":$storage_type,
+                        "uint64_t":$size,
+                        "uint64_t":$offset,
+                        "bool":$is_signed);
+
+  let assemblyFormat = "`<` struct($name, $storage_type, $size, $offset, $is_signed) `>`";
+
+  let builders = [
+    AttrBuilder<(ins "StringRef":$name,
+                     "Type":$storage_type,
+                     "uint64_t":$size,
+                     "uint64_t":$offset,
+                     "bool":$is_signed
+                     ), [{
+      return $_get($_ctxt, StringAttr::get($_ctxt, name), storage_type, size, offset, is_signed);
+    }]>
+  ];
+}
+
 #endif // MLIR_CIR_DIALECT_CIR_ATTRS

clang/include/clang/CIR/Dialect/IR/CIROps.td

@@ -1415,6 +1415,154 @@ def VTableAddrPointOp : CIR_Op<"vtable.address_point",
   let hasVerifier = 1;
 }
 
+//===----------------------------------------------------------------------===//
+// SetBitfieldOp
+//===----------------------------------------------------------------------===//
+
+def SetBitfieldOp : CIR_Op<"set_bitfield"> {
+  let summary = "Set a bitfield";
+  let description = [{ 
+    The `cir.set_bitfield` operation provides a store-like access to 
+    a bit field of a record.
+
+    It expects an address of a storage where to store, a type of the storage,
+    a value being stored, a name of a bit field, a pointer to the storage in the
+    base record, a size of the storage, a size the bit field, an offset 
+    of the bit field and a sign. Returns a value being stored.
+
+    Example.
+    Suppose we have a struct with multiple bitfields stored in
+    different storages. The `cir.set_bitfield` operation sets the value
+    of the bitfield.
+    ```C++
+    typedef struct {
+      int a : 4;
+      int b : 27;
+      int c : 17;
+      int d : 2;
+      int e : 15;
+    } S;
+
+    void store_bitfield(S& s) {
+      s.d = 3;
+    }
+    ```
+
+    ```mlir
+    // 'd' is in the storage with the index 1
+    !struct_type = !cir.struct<struct "S" {!cir.int<u, 32>, !cir.int<u, 32>, !cir.int<u, 16>} #cir.record.decl.ast>
+    #bfi_d = #cir.bitfield_info<name = "d", storage_type = !u32i, size = 2, offset = 17, is_signed = true>
+
+    %1 = cir.const(#cir.int<3> : !s32i) : !s32i
+    %2 = cir.load %0 : cir.ptr <!cir.ptr<!struct_type>>, !cir.ptr<!struct_type>
+    %3 = cir.get_member %2[1] {name = "d"} : !cir.ptr<!struct_type> -> !cir.ptr<!u32i>
+    %4 = cir.set_bitfield(#bfi_d, %3 : !cir.ptr<!u32i>, %1 : !s32i) -> !s32i
+    ```
+   }];
+
+  let arguments = (ins
+    AnyType:$dst,
+    AnyType:$src,
+    BitfieldInfoAttr:$bitfield_info
+  );
+
+  let results = (outs CIR_IntType:$result);
+
+  let assemblyFormat = [{ `(`$bitfield_info`,` $dst`:`type($dst)`,`
+    $src`:`type($src) `)`  attr-dict `->` type($result) }];
+  
+  let builders = [
+    OpBuilder<(ins "Type":$type,
+                   "Value":$dst,
+                   "Type":$storage_type,
+                   "Value":$src,
+                   "StringRef":$name,
+                   "unsigned":$size, 
+                   "unsigned":$offset,
+                   "bool":$is_signed
+                   ),
+   [{      
+      BitfieldInfoAttr info = 
+        BitfieldInfoAttr::get($_builder.getContext(), 
+                              name, storage_type,
+                              size, offset, is_signed);
+      build($_builder, $_state, type, dst, src, info);
+    }]>
+  ];
+}
+
+//===----------------------------------------------------------------------===//
+// GetBitfieldOp
+//===----------------------------------------------------------------------===//
+
+def GetBitfieldOp : CIR_Op<"get_bitfield"> {
+  let summary = "Get a bitfield";
+  let description = [{ 
+    The `cir.get_bitfield` operation provides a load-like access to
+    a bit field of a record.
+
+    It expects a name if a bit field, a pointer to a storage in the
+    base record, a type of the storage, a name of the bitfield,
+    a size the bit field, an offset of the bit field and a sign.
+
+    Example:
+    Suppose we have a struct with multiple bitfields stored in
+    different storages. The `cir.get_bitfield` operation gets the value
+    of the bitfield
+    ```C++
+    typedef struct {
+      int a : 4;
+      int b : 27;
+      int c : 17;
+      int d : 2;
+      int e : 15;
+    } S;
+
+    int load_bitfield(S& s) {
+      return s.d;
+    }
+    ```
+
+    ```mlir
+    // 'd' is in the storage with the index 1
+    !struct_type = !cir.struct<struct "S" {!cir.int<u, 32>, !cir.int<u, 32>, !cir.int<u, 16>} #cir.record.decl.ast>
+    #bfi_d = #cir.bitfield_info<name = "d", storage_type = !u32i, size = 2, offset = 17, is_signed = true>
+
+    %2 = cir.load %0 : cir.ptr <!cir.ptr<!struct_type>>, !cir.ptr<!struct_type>
+    %3 = cir.get_member %2[1] {name = "d"} : !cir.ptr<!struct_type> -> !cir.ptr<!u32i>
+    %4 = cir.get_bitfield(#bfi_d, %3 : !cir.ptr<!u32i>) -> !s32i
+    ```
+    }];
+
+  let arguments = (ins
+    AnyType:$addr,    
+    BitfieldInfoAttr:$bitfield_info
+    );
+
+  let results = (outs CIR_IntType:$result);
+
+  let assemblyFormat = [{ `(`$bitfield_info `,` $addr attr-dict `:` 
+   type($addr) `)` `->` type($result) }];
+
+  let builders = [
+    OpBuilder<(ins "Type":$type,
+                   "Value":$addr,
+                   "Type":$storage_type,
+                   "StringRef":$name,
+                   "unsigned":$size,
+                   "unsigned":$offset,
+                   "bool":$is_signed
+                   ),
+   [{
+      BitfieldInfoAttr info = 
+        BitfieldInfoAttr::get($_builder.getContext(), 
+                              name, storage_type,
+                              size, offset, is_signed);
+      build($_builder, $_state, type, addr, info);
+    }]>
+  ];
+}
+
 //===----------------------------------------------------------------------===//
 // GetMemberOp
 //===----------------------------------------------------------------------===//

clang/lib/CIR/CodeGen/CIRGenBuilder.h

@@ -10,6 +10,7 @@
 #define LLVM_CLANG_LIB_CIR_CIRGENBUILDER_H
 
 #include "Address.h"
+#include "CIRGenRecordLayout.h"
 #include "CIRDataLayout.h"
 #include "CIRGenTypeCache.h"
 #include "UnimplementedFeatureGuarding.h"
@@ -661,6 +662,26 @@ class CIRGenBuilderTy : public CIRBaseBuilderTy {
         global.getLoc(), getPointerTo(global.getSymType()), global.getName());
   }
 
+  mlir::Value createGetBitfield(mlir::Location loc, mlir::Type resultType,
+                                mlir::Value addr, mlir::Type storageType,
+                                const CIRGenBitFieldInfo &info,
+                                bool useVolatile) {
+    auto offset = useVolatile ? info.VolatileOffset : info.Offset;
+    return create<mlir::cir::GetBitfieldOp>(loc, resultType, addr, storageType,
+                                            info.Name, info.Size,
+                                            offset, info.IsSigned);
+  }
+
+  mlir::Value createSetBitfield(mlir::Location loc, mlir::Type resultType,
+                                mlir::Value dstAddr, mlir::Type storageType,
+                                mlir::Value src, const CIRGenBitFieldInfo &info,
+                                bool useVolatile) {
+    auto offset = useVolatile ? info.VolatileOffset : info.Offset;
+    return create<mlir::cir::SetBitfieldOp>(
+        loc, resultType, dstAddr, storageType, src, info.Name,
+        info.Size, offset, info.IsSigned);
+  }
+
   /// Create a pointer to a record member.
   mlir::Value createGetMember(mlir::Location loc, mlir::Type result,
                               mlir::Value base, llvm::StringRef name,