[llvm] [NFC][MC][Decoder] Extract fixed pieces of decoder code into new header file (PR #154802)

[Sergei Barannikov via llvm-commits]

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@@ -0,0 +1,67 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// Disassembler decoder helper functions.
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_MC_MCDECODER_H
+#define LLVM_MC_MCDECODER_H
+
+#include "llvm/MC/MCDisassembler/MCDisassembler.h"
+#include "llvm/Support/MathExtras.h"
+#include <cassert>
+
+namespace llvm::MCD {
+
+// Helper to propagate SoftFail status. Returns false if the status is Fail;
+// callers are expected to early-exit in that condition. (Note, the '&' operator
+// is correct to propagate the values of this enum; see comment on 'enum
+// DecodeStatus'.)
+inline bool Check(MCDisassembler::DecodeStatus &Out,
+                  MCDisassembler::DecodeStatus In) {
+  Out = static_cast<MCDisassembler::DecodeStatus>(Out & In);
+  return Out != MCDisassembler::Fail;
+}
+
+// fieldFromInstruction - Extracts a given span of bits from the instruction
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s-barannikov wrote:

Should drop function name from the comment (per coding standard).

https://github.com/llvm/llvm-project/pull/154802