fix: align GPR register files with review feedback

Changes:
- rename schema from register_schema.json to register_file_schema.json,
  remove "$ref": "#/$defs/register_file" from bottom of the schema,
  and introduce register_file_name.
- drop per-register length and index fields, make abi mnemonics an
  array, and add 'caller_saved'/'callee_saved' booleans with default
  value of 'false'.
- remove the 'count' helper in favor of conditioning individual
  register entries directly and infer indices from position.
- fix the description for XLEN behavior and remove empty role arrays.
- update the register-file section of README.adoc so the example
  mirrors the new schema.
- register_file.rb: expose register data via '#data' and return
  Sorbet enum values for roles.

Signed-off-by: Animesh Agarwal <[email protected]>

Author: AnimeshAgarwal28

spec/schemas/register_schema.json renamed to spec/schemas/register_file_schema.json

@@ -5,50 +5,46 @@
   "description": "Schema for describing a register file",
 
   "$defs": {
-    "count_variant": {
-      "type": "object",
-      "required": ["value", "when"],
-      "additionalProperties": false,
-      "properties": {
-        "value": {
-          "type": "integer",
-          "description": "Override count when condition is satisfied"
-        },
-        "when": {
-          "$ref": "schema_defs.json#/$defs/requires_entry"
-        },
-        "description": {
-          "$ref": "schema_defs.json#/$defs/spec_text"
-        }
-      }
-    },
     "register_entry": {
       "type": "object",
-      "required": ["name", "index"],
+      "required": ["name"],
       "additionalProperties": false,
       "properties": {
         "name": {
           "$ref": "schema_defs.json#/$defs/register_name"
         },
-        "abi_mnemonic": {
-          "$ref": "schema_defs.json#/$defs/register_alias"
-        },
-        "index": {
-          "type": "integer",
-          "minimum": 0,
-          "description": "Register index"
+        "abi_mnemonics": {
+          "type": "array",
+          "items": {
+            "$ref": "schema_defs.json#/$defs/register_alias"
+          },
+          "minItems": 1,
+          "uniqueItems": true,
+          "description": "ABI mnemonic names for the register"
         },
         "description": {
           "$ref": "schema_defs.json#/$defs/spec_text"
         },
-        "definedBy": {
-          "$ref": "schema_defs.json#/$defs/requires_entry"
-        },
         "when": {
           "$ref": "schema_defs.json#/$defs/requires_entry"
         },
-        "length": {
-          "$ref": "schema_defs.json#/$defs/bit_length_value"
+        "sw_read()": {
+          "type": "string",
+          "description": "Function that returns the value of the register when read by software. Use this to define special behavior for registers (e.g., x0 always reads as zero)."
+        },
+        "sw_write(value)": {
+          "type": "string",
+          "description": "Function implementing custom write behavior for the register. Given a 'value', return either the value to be written or a modified value. Use this to define special behavior for registers (e.g., x0 ignores writes)."
+        },
+        "caller_saved": {
+          "type": "boolean",
+          "default": false,
+          "description": "Whether the register is caller-saved"
+        },
+        "callee_saved": {
+          "type": "boolean",
+          "default": false,
+          "description": "Whether the register is callee-saved"
         },
         "roles": {
           "type": "array",
@@ -63,8 +59,6 @@
               "frame_pointer",
               "return_value",
               "argument",
-              "caller_saved",
-              "callee_saved",
               "temporary"
             ]
           },
@@ -80,23 +74,23 @@
         "name",
         "long_name",
         "description",
-        "length",
+        "register_length",
         "registers"
       ],
       "additionalProperties": false,
       "properties": {
         "$schema": {
           "type": "string",
           "format": "uri-reference",
-          "const": "register_schema.json#",
+          "const": "register_file_schema.json#",
           "description": "Path to schema, relative to <UDB ROOT>/schemas"
         },
         "kind": {
           "type": "string",
           "const": "register_file"
         },
         "name": {
-          "$ref": "schema_defs.json#/$defs/register_name"
+          "$ref": "schema_defs.json#/$defs/register_file_name"
         },
         "long_name": {
           "type": "string"
@@ -111,34 +105,9 @@
           "type": "string",
           "enum": ["general_purpose", "floating_point", "vector"]
         },
-        "length": {
+        "register_length": {
           "$ref": "schema_defs.json#/$defs/bit_length_value"
         },
-        "count": {
-          "oneOf": [
-            {
-              "type": "integer",
-              "minimum": 0
-            },
-            {
-              "type": "object",
-              "required": ["default"],
-              "additionalProperties": false,
-              "properties": {
-                "default": {
-                  "type": "integer",
-                  "minimum": 0
-                },
-                "variants": {
-                  "type": "array",
-                  "items": {
-                    "$ref": "#/$defs/count_variant"
-                  }
-                }
-              }
-            }
-          ]
-        },
         "registers": {
           "type": "array",
           "minItems": 1,
@@ -152,6 +121,5 @@
         }
       }
     }
-  },
-  "$ref": "#/$defs/register_file"
+  }
 }

spec/schemas/schema_defs.json

@@ -52,7 +52,8 @@
         },
         {
           "type": "string",
-          "minLength": 1
+          "minLength": 1,
+          "enum": ["MXLEN"]
         }
       ]
     },
@@ -61,6 +62,11 @@
       "pattern": "^[A-Za-z][A-Za-z0-9_.-]*$",
       "description": "Register name"
     },
+    "register_file_name": {
+      "type": "string",
+      "pattern": "^[A-Za-z][A-Za-z0-9_.-]*$",
+      "description": "Register file name"
+    },
     "register_alias": {
       "type": "string",
       "pattern": "^[A-Za-z][A-Za-z0-9_.-]*$",

spec/std/isa/README.adoc

@@ -29,8 +29,8 @@ Three standard configs are present:
  * `rv64`: A configuration where only `MXLEN` is known to be 64, i.e., the RV64 ISA.
 
 The architecture is specified in a series of https://en.wikipedia.org/wiki/YAML[YAML]
-files for _Extensions_, _Instructions_, _Registers_, and _Control and Status Registers (CSRs)_.
-Each extension/instruction/register/CSR has its own file.
+files for _Extensions_, _Instructions_, _RegFiles_, and _Control and Status Registers (CSRs)_.
+Each extension/instruction/regfile/CSR has its own file.
 
 == Flow
 
@@ -142,38 +142,39 @@ H: # <1>
 
 === Instructions
 
-=== Registers
+=== Register Files
 
 .Example register file specification
 [source,yaml]
 ----
-$schema: register_schema.json#
+$schema: register_file_schema.json#
 kind: register_file
 name: X
 long_name: Integer General Purpose Registers
 definedBy: I
 register_class: general_purpose
-length: XLEN # <1>
-count:
-  default: 32
-  variants:
-    - value: 16
-      when: { name: E } # <2>
+register_length: MXLEN # <1>
 registers:
-  - name: x0
-    index: 0
-    abi_mnemonic: zero # <3>
+  - name: x0    # <2>
+    abi_mnemonics: [zero] # <3>
     roles: [zero]
+    sw_read(): | # <4>
+      return 0;
+    sw_write(value): |
+      # x0 ignores all writes
   - name: x1
-    index: 1
-    abi_mnemonic: ra
+    abi_mnemonics: [ra]
     roles: [return_address]
+  - name: x8
+    abi_mnemonics: [s0, fp] # <5>
+    roles: [callee_saved, frame_pointer]
 ----
 
-<1> Register files are defined independently of the resolved XLEN; individual register entries
-    may override the default bit length when necessary.
-<2> Conditional presence uses the same `when`/`definedBy` semantics as other database objects.
-<3> Entries can record ABI mnemonics and semantic roles.
+<1> Registers can have either a fixed architecture width or take their width from a parameter (e.g., MXLEN, VLEN).
+<2> Each register has a unique name (e.g., x0, x1, x2, etc.). The register's index is inferred from its position in the array (starting from 0).
+<3> Registers can optionally have ABI mnemonics (e.g., ra, sp, fp, etc.).
+<4> Individual registers can define `sw_read()` and `sw_write()` for special behavior (e.g., x0 hardwired to zero).
+<5> A register can have multiple ABI mnemonics (e.g., x8 is known as both s0 and fp).
 
 [source,yaml]
 ----