[LLHD] Add extract field operations (llvm#35)

* [LLHD] Add extract field operations

* Add operations to statically and dynamically extract an element from
a vector or tuple
* They can also operate on signals by returning an alias signal to the
specified element of the underlying type of the target signal, this
means they don't perform any kind of probing like the llhd.prb
instruction

* Change names of operations, improve error message

* llhd.extf -> llhd.extract_element
* llhd.dextf -> llhd.dyn_extract_element

* 2-space indent

include/circt/Dialect/LLHD/IR/ExtractOps.td

@@ -101,3 +101,122 @@ def LLHD_DextsOp : LLHD_Op<"dexts", [
     unsigned getTargetWidth() { return getLLHDTypeWidth(target().getType()); }
   }];
 }
+
+def LLHD_ExtractElementOp : LLHD_Op<"extract_element", [
+    NoSideEffect,
+    PredOpTrait<"'index' has to be smaller than the width of the 'target' type",
+      CPred<"$index.cast<IntegerAttr>().getInt() < getTargetWidth()">>,
+    TypesMatchWith<
+      "'result' type must match the type of 'target' at position 'index', or "
+      "in case 'target' is a signal, it must be a signal of the underlying type"
+      " of 'target' at position 'index'",
+      "target", "result",
+      "($_self.isa<llhd::SigType>() "
+        "? llhd::SigType::get("
+          "getElementTypeAtIndex($index.cast<IntegerAttr>().getInt())) "
+        ": getElementTypeAtIndex($index.cast<IntegerAttr>().getInt()))">
+  ]> {
+  let summary = [{
+    Extract an element from a vector, tuple, or signal of a vector or tuple.
+  }];
+  let description = [{
+    The `llhd.extract_element` operation allows access to an element of the
+    `$target` operand. The `$index` attribute defines the index of the element
+    to extract. If `%target` is a signal, a new subsignal aliasing the element
+    will be returned.
+
+    Example:
+
+    ```mlir
+    %0 = constant dense<[1,2,3]> : vector<3xi8>
+    %1 = llhd.extract_element %0, 0 : vector<3xi8> -> i8
+
+    %2 = llhd.sig %0 : vector<3xi8>
+    %3 = llhd.extract_element %2, 0 : !llhd.sig<vector<3xi8>> -> !llhd.sig<i8>
+
+    %4 = llhd.const 8 : i16
+    %5 = llhd.tuple %0, %4 : tuple<vector<3xi8>, i16>
+    %6 = llhd.extract_element %5, 1 : tuple<vector<3xi8>, i16> -> i16
+    ```
+  }];
+
+  let arguments = (ins AnyTypeOf<[
+      AnyVector,
+      AnyTuple,
+      LLHD_SigType<[AnyVector, AnyTuple]>
+    ]>: $target,
+    IndexAttr: $index);
+
+  let results = (outs AnyType: $result);
+
+  let assemblyFormat = [{
+    $target `,` $index attr-dict `:` type($target) `->` type($result)
+  }];
+
+  let extraClassDeclaration = [{
+    unsigned getTargetWidth() { return getLLHDTypeWidth(target().getType()); };
+
+    Type getElementTypeAtIndex(unsigned index) {
+      Type targetType = target().getType();
+      if (auto sig = targetType.dyn_cast<llhd::SigType>())
+        targetType = sig.getUnderlyingType();
+      if (auto vec = targetType.dyn_cast<VectorType>())
+        return vec.getElementType();
+      return targetType.dyn_cast<TupleType>().getTypes()[index];
+    }
+  }];
+}
+
+def LLHD_DynamicExtractElementOp : LLHD_Op<"dyn_extract_element", [
+  NoSideEffect,
+  TypesMatchWith<"'result' must be the element type of the 'target' vector, in "
+    "case 'target' is a signal of a vector, 'result' also is a signal of the "
+    "vector element type",
+    "target", "result",
+    "($_self.isa<llhd::SigType>() ? llhd::SigType::get(getElementType()) "
+                                 ": getElementType())">
+  ]> {
+  let summary = [{
+    Dynamically extract an element from a vector or signal of vector.
+  }];
+  let description = [{
+    The `llhd.dyn_extract_element` operation allows to dynamically access an
+    element of the `$target` operand. The `$index` operand defines the index of
+    the element to extract. If `%target` is a signal, a new subsignal aliasing
+    the element will be returned.
+
+    Example:
+
+    ```mlir
+    %index = llhd.const 1 : i2
+
+    %0 = constant dense<[1,2,3]> : vector<3xi8>
+    %1 = llhd.dyn_extract_element %0, %index : (vector<3xi8>, i2) -> i8
+
+    %2 = llhd.sig %0 : vector<3xi8>
+    %3 = llhd.dyn_extract_element %2, %index
+      : (!llhd.sig<vector<3xi8>>, i2) -> !llhd.sig<i8>
+    ```
+  }];
+
+  let arguments = (ins
+    AnyTypeOf<[AnyVector, LLHD_SigType<[AnyVector]>]>: $target,
+    AnySignlessInteger: $index);
+
+  let results = (outs AnyType: $result);
+
+  let assemblyFormat = [{
+    $target `,` $index attr-dict `:` functional-type(operands, results)
+  }];
+
+  let extraClassDeclaration = [{
+    unsigned getTargetWidth() { return getLLHDTypeWidth(target().getType()); }
+
+    Type getElementType() {
+      Type targetType = target().getType();
+      if (auto sig = targetType.dyn_cast<llhd::SigType>())
+        targetType = sig.getUnderlyingType();
+      return targetType.dyn_cast<VectorType>().getElementType();
+    }
+  }];
+}