ir/value: Add a GetImmediateAsS64() function

Provides a signed analogue to GetImmediateAsU64() for consistency with
both integral classes when it comes to signed/unsigned..

src/frontend/ir/value.cpp

@@ -5,6 +5,7 @@
  */
 
 #include "common/assert.h"
+#include "common/bit_util.h"
 #include "frontend/ir/microinstruction.h"
 #include "frontend/ir/opcodes.h"
 #include "frontend/ir/type.h"
@@ -155,6 +156,25 @@ Cond Value::GetCond() const {
     return inner.imm_cond;
 }
 
+s64 Value::GetImmediateAsS64() const {
+    ASSERT(IsImmediate());
+
+    switch (GetType()) {
+    case IR::Type::U1:
+        return s64(GetU1());
+    case IR::Type::U8:
+        return s64(Common::SignExtend<8, u64>(GetU8()));
+    case IR::Type::U16:
+        return s64(Common::SignExtend<16, u64>(GetU16()));
+    case IR::Type::U32:
+        return s64(Common::SignExtend<32, u64>(GetU32()));
+    case IR::Type::U64:
+        return s64(GetU64());
+    default:
+        ASSERT_MSG(false, "GetImmediateAsS64 called on an incompatible Value type.");
+    }
+}
+
 u64 Value::GetImmediateAsU64() const {
     ASSERT(IsImmediate());
 

src/frontend/ir/value.h

@@ -67,7 +67,15 @@ public:
     Cond GetCond() const;
 
     /**
-     * Retrieves the immediate of a Value instance.
+     * Retrieves the immediate of a Value instance as a signed 64-bit value.
+     *
+     * @pre The value contains either a U1, U8, U16, U32, or U64 value.
+     *      Breaking this precondition will cause an assertion to be invoked.
+     */
+    s64 GetImmediateAsS64() const;
+
+    /**
+     * Retrieves the immediate of a Value instance as an unsigned 64-bit value.
      *
      * @pre The value contains either a U1, U8, U16, U32, or U64 value.
      *      Breaking this precondition will cause an assertion to be invoked.