cpu: Result refactoring

The Result union used to collect the result of an instruction is now a
class of its own, with its constructor, and explicit casting methods for
cleanliness.

This is also a stepping stone to have vector registers, and instructions
that produce a vector register as output.

Change-Id: I6f40c11cb5e835d8b11f7804a4e967aff18025b9
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2703
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

1 files changed, 131 insertions, 0 deletions

diff --git a/src/cpu/inst_res.hh b/src/cpu/inst_res.hh
new file mode 100644
index 000000000..f6f14fe19
--- /dev/null
+++ b/src/cpu/inst_res.hh
@@ -0,0 +1,131 @@
+/*
+ * Copyright (c) 2016 ARM Limited
+ * All rights reserved
+ *
+ * The license below extends only to copyright in the software and shall
+ * not be construed as granting a license to any other intellectual
+ * property including but not limited to intellectual property relating
+ * to a hardware implementation of the functionality of the software
+ * licensed hereunder.  You may use the software subject to the license
+ * terms below provided that you ensure that this notice is replicated
+ * unmodified and in its entirety in all distributions of the software,
+ * modified or unmodified, in source code or in binary form.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Nathanael Premillieu
+ */
+
+#ifndef __CPU_INST_RES_HH__
+#define __CPU_INST_RES_HH__
+
+#include <type_traits>
+
+#include "arch/generic/types.hh"
+
+class InstResult {
+  public:
+    union MultiResult {
+        uint64_t integer;
+        double dbl;
+        MultiResult() {}
+    };
+
+    enum class ResultType {
+        Scalar,
+        NumResultTypes,
+        Invalid
+    };
+
+  private:
+    MultiResult result;
+    ResultType type;
+
+  public:
+    /** Default constructor creates an invalid result. */
+    InstResult() : type(ResultType::Invalid) { }
+    /** Scalar result from scalar. */
+    template<typename T>
+    explicit InstResult(T i, const ResultType& t) : type(t) {
+        static_assert(std::is_integral<T>::value ^
+                        std::is_floating_point<T>::value,
+                "Parameter type is neither integral nor fp, or it is both");
+        if (std::is_integral<T>::value) {
+            result.integer = i;
+        } else if (std::is_floating_point<T>::value) {
+            result.dbl = i;
+        }
+    }
+
+    /**
+     * Result comparison
+     * Two invalid results always differ.
+     */
+    bool operator==(const InstResult& that) const {
+        if (this->type != that.type)
+            return false;
+        switch (type) {
+        case ResultType::Scalar:
+            return result.integer == that.result.integer;
+        case ResultType::Invalid:
+            return false;
+        default:
+            panic("Unknown type of result: %d\n", (int)type);
+        }
+    }
+
+    bool operator!=(const InstResult& that) const {
+        return !operator==(that);
+    }
+
+    /** Checks */
+    /** @{ */
+    /** Is this a scalar result?. */
+    bool isScalar() const { return type == ResultType::Scalar; }
+    /** Is this a valid result?. */
+    bool isValid() const { return type != ResultType::Invalid; }
+    /** @} */
+
+    /** Explicit cast-like operations. */
+    /** @{ */
+    const uint64_t&
+    asInteger() const
+    {
+        assert(isScalar());
+        return result.integer;
+    }
+
+    /** Cast to integer without checking type.
+     * This is required to have the o3 cpu checker happy, as it
+     * compares results as integers without being fully aware of
+     * their nature. */
+    const uint64_t&
+    asIntegerNoAssert() const
+    {
+        return result.integer;
+    }
+    /** @} */
+};
+
+#endif // __CPU_INST_RES_HH__