Add Zclsd extension YAML (#577)

This PR adds the Zclsd extension to the database. Zclsd introduces
compressed load/store pair instructions for RV32 by reusing RV64-only
instruction encodings, which helps improve code density and performance
when leveraging a wider than XLEN memory interface. It defines 16-bit
instruction encodings and utilizes the same even-odd register pairing as
the Zdinx extension. Additionally, Zclsd depends on the Zilsd and Zca
extensions, and it is incompatible with Zcf due to overlapping encodings
Closes #572

---------

Signed-off-by: Shehroz Kashif <[email protected]>
Co-authored-by: Paul Clarke <[email protected]>

Author: Shehrozkashif

arch/ext/Zclsd.yaml

@@ -0,0 +1,16 @@
+$schema: "ext_schema.json#"
+kind: extension
+name: Zclsd
+conflicts: Zcf
+long_name: Compressed Load/Store Pair for RV32
+description: |
+  This extension adds load and store instructions using register pairs. It does so by reusing existing instruction encodings which are RV64-only. The specification defines 16-bit encodings.
+  Load and store instructions will use the same definition of even-odd pairs as defined by the Zdinx extension.
+  The extension improves static code density, by replacing two separate load or store instructions with a single one. In addition, it can provide a performance improvement for implementations that can make use of a wider than XLEN memory interface.
+type: unprivileged
+versions:
+  - version: "1.0"
+    state: ratified
+    ratification_date: "2025-02"
+    requires:
+      allOf: [ Zilsd, Zca ]

arch/inst/C/c.ld.yaml

@@ -5,26 +5,39 @@ kind: instruction
 name: c.ld
 long_name: Load double
 description: |
-  Loads a 64-bit value from memory into register rd.
+  Loads a 64-bit value from memory into register xd.
   It computes an effective address by adding the zero-extended offset, scaled by 8,
-  to the base address in register rs1.
-  It expands to `ld` `rd, offset(rs1)`.
+  to the base address in register xs1.
+  It expands to `ld` `xd, offset(xs1)`.
+  For RV32, if the Zclsd extension is enabled, this instruction loads a 64-bit value into registers xd and xd+1. It computes an effective address by adding the zero-extended imm, scaled by 8, to the base address in register xs1.
 definedBy:
   anyOf:
     - C
     - Zca
-base: 64
+    - Zclsd
 assembly: xd, imm(xs1)
 encoding:
-  match: 011-----------00
-  variables:
-    - name: imm
-      location: 6-5|12-10
-      left_shift: 3
-    - name: rd
-      location: 4-2
-    - name: rs1
-      location: 9-7
+  RV32:
+    match: 011-----------00
+    variables:
+      - name: imm
+        location: 6-5|12-10
+        left_shift: 3
+      - name: xd
+        location: 4-2
+        not: [1, 3, 5, 7]
+      - name: xs1
+        location: 9-7
+  RV64:
+    match: 011-----------00
+    variables:
+      - name: imm
+        location: 6-5|12-10
+        left_shift: 3
+      - name: xd
+        location: 4-2
+      - name: xs1
+        location: 9-7
 access:
   s: always
   u: always
@@ -35,9 +48,18 @@ operation(): |
     raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
   }
 
-  XReg virtual_address = X[creg2reg(rs1)] + imm;
-
-  X[creg2reg(rd)] = sext(read_memory<64>(virtual_address, $encoding), 64);
+  if (xlen() == 32) {
+    if (implemented?(ExtensionName::Zclsd)) {
+      Bits<64> val = read_memory<64>(X[creg2reg(xs1)] + imm, $encoding);
+      X[creg2reg(xd)] = val[31:0];
+      X[creg2reg(xd + 1)] = val[63:32];
+    } else {
+      raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
+    }
+  } else {
+    XReg virtual_address = X[creg2reg(xs1)] + imm;
+    X[creg2reg(xd)] = sext(read_memory<64>(virtual_address, $encoding), 64);
+  }
 
 # SPDX-SnippetBegin
 # SPDX-FileCopyrightText: 2017-2025 Contributors to the RISCV Sail Model <https://github.com/riscv/sail-riscv/blob/master/LICENCE>
@@ -57,13 +79,13 @@ sail(): |
           TR_Address(paddr, _) =>
             match (width) {
               BYTE =>
-                process_load(rd, vaddr, mem_read(Read(Data), paddr, 1, aq, rl, false), is_unsigned),
+                process_load(xd, vaddr, mem_read(Read(Data), paddr, 1, aq, rl, false), is_unsigned),
               HALF =>
-                process_load(rd, vaddr, mem_read(Read(Data), paddr, 2, aq, rl, false), is_unsigned),
-              WORD =>
-                process_load(rd, vaddr, mem_read(Read(Data), paddr, 4, aq, rl, false), is_unsigned),
+                process_load(xd, vaddr, mem_read(Read(Data), paddr, 2, aq, rl, false), is_unsigned),
+              WOxD =>
+                process_load(xd, vaddr, mem_read(Read(Data), paddr, 4, aq, rl, false), is_unsigned),
               DOUBLE if sizeof(xlen) >= 64 =>
-                process_load(rd, vaddr, mem_read(Read(Data), paddr, 8, aq, rl, false), is_unsigned),
+                process_load(xd, vaddr, mem_read(Read(Data), paddr, 8, aq, rl, false), is_unsigned),
               _ => report_invalid_width(__FILE__, __LINE__, width, "load")
             }
         }

arch/inst/C/c.ldsp.yaml

@@ -6,26 +6,34 @@ name: c.ldsp
 long_name: Load doubleword from stack pointer
 description: |
   C.LDSP is an RV64C/RV128C-only instruction that loads a 64-bit value from memory
-  into register rd.
+  into register xd.
   It computes its effective address by adding the zero-extended offset, scaled by 8,
   to the stack pointer, x2.
-  It expands to `ld` `rd, offset(x2)`.
-  C.LDSP is only valid when rd ≠ x0 the code points with rd=x0 are reserved.
+  It expands to `ld xd, offset(x2)`.
+  C.LDSP is only valid when xd ≠ x0; code points with xd=x0 are reserved.
 definedBy:
   anyOf:
     - C
     - Zca
-base: 64
 assembly: xd, imm(sp)
 encoding:
-  match: 011-----------10
-  variables:
-    - name: imm
-      location: 4-2|12|6-5
-      left_shift: 3
-    - name: rd
-      location: 11-7
-      not: 0
+  RV32:
+    match: 011-----------10
+    variables:
+      - name: imm
+        location: 4-2|12|6-5
+        left_shift: 3
+      - name: xd
+        location: 11-7
+        not: [0, 1, 3, 5, 7]
+  RV64:
+    match: 011-----------10
+    variables:
+      - name: imm
+        location: 4-2|12|6-5
+        left_shift: 3
+      - name: xd
+        location: 11-7
 access:
   s: always
   u: always
@@ -37,5 +45,11 @@ operation(): |
   }
 
   XReg virtual_address = X[2] + imm;
+  Bits<64> value = read_memory<64>(virtual_address, $encoding);
 
-  X[rd] = read_memory<64>(virtual_address, $encoding);
+  if (xlen()== 64) {
+    X[creg2reg(xd)] = value;
+  } else if (xlen() == 32) {
+    X[creg2reg(xd)]     = value[31:0];
+    X[creg2reg(xd) + 1] = value[63:32];
+  }

arch/inst/C/c.sd.yaml

@@ -5,26 +5,38 @@ kind: instruction
 name: c.sd
 long_name: Store double
 description: |
-  Stores a 64-bit value in register rs2 to memory.
+  For RV64, store a 64-bit value in register xs2 to memory. For RV32 with Zclsd extension, store a 64-bit value from the combined values in register pair [xs2, xs2+1] to memory.
   It computes an effective address by adding the zero-extended offset, scaled by 8,
-  to the base address in register rs1.
-  It expands to `sd` `rs2, offset(rs1)`.
+  to the base address in register xs1.
+  It expands to `sd` `xs2, offset(xs1)`.
 definedBy:
   anyOf:
     - C
     - Zca
-base: 64
+    - Zclsd
 assembly: xs2, imm(xs1)
 encoding:
-  match: 111-----------00
-  variables:
-    - name: imm
-      location: 6-5|12-10
-      left_shift: 3
-    - name: rs2
-      location: 4-2
-    - name: rs1
-      location: 9-7
+  RV32:
+    match: 111-----------00
+    variables:
+      - name: imm
+        location: 6-5|12-10
+        left_shift: 3
+      - name: xs2
+        location: 4-2
+        not: [1, 3, 5, 7]
+      - name: xs1
+        location: 9-7
+  RV64:
+    match: 111-----------00
+    variables:
+      - name: imm
+        location: 6-5|12-10
+        left_shift: 3
+      - name: xs2
+        location: 4-2
+      - name: xs1
+        location: 9-7
 access:
   s: always
   u: always
@@ -35,6 +47,15 @@ operation(): |
     raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
   }
 
-  XReg virtual_address = X[creg2reg(rs1)] + imm;
+  XReg virtual_address = X[creg2reg(xs1)] + imm;
 
-  write_memory<64>(virtual_address, X[creg2reg(rs2)], $encoding);
+  if (xlen() == 32) {
+    if (implemented?(ExtensionName::Zclsd)) {
+      Bits<64> data = {X[creg2reg(xs2) + 1], X[creg2reg(xs2)]};
+      write_memory<64>(virtual_address, data, $encoding);
+    } else {
+      raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
+    }
+  } else {
+    write_memory<64>(virtual_address, X[creg2reg(xs2)], $encoding);
+  }

arch/inst/C/c.sdsp.yaml

@@ -13,16 +13,26 @@ definedBy:
   anyOf:
     - C
     - Zca
-base: 64
+    - Zclsd
 assembly: xs2, imm(sp)
 encoding:
-  match: 111-----------10
-  variables:
-    - name: imm
-      location: 9-7|12-10
-      left_shift: 3
-    - name: rs2
-      location: 6-2
+  RV32:
+    match: 111-----------10
+    variables:
+      - name: xs2
+        location: 6-2
+        not: [1, 3, 5, 7]
+      - name: imm
+        location: 9-7|12-10
+        left_shift: 3
+  RV64:
+    match: 111-----------10
+    variables:
+      - name: xs2
+        location: 6-2
+      - name: imm
+        location: 9-7|12-10
+        left_shift: 3
 access:
   s: always
   u: always
@@ -35,4 +45,13 @@ operation(): |
 
   XReg virtual_address = X[2] + imm;
 
-  write_memory<64>(virtual_address, X[rs2], $encoding);
+  if (xlen() == 32) {
+    if (implemented?(ExtensionName::Zclsd)) {
+      Bits<64> data = {X[creg2reg(xs2) + 1], X[creg2reg(xs2)]};
+      write_memory<64>(virtual_address, data, $encoding);
+    } else {
+      raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
+    }
+  } else {
+    write_memory<64>(virtual_address, X[creg2reg(xs2)], $encoding);
+  }