Remove the unused sigid argument purpose (#5753)

cranelift/codegen/src/ir/extfunc.rs

@@ -252,12 +252,6 @@ pub enum ArgumentPurpose {
     /// used as a base pointer for `vmctx` global values.
     VMContext,
 
-    /// A signature identifier.
-    ///
-    /// This is a special-purpose argument used to identify the calling convention expected by the
-    /// caller in an indirect call. The callee can verify that the expected signature ID matches.
-    SignatureId,
-
     /// A stack limit pointer.
     ///
     /// This is a pointer to a stack limit. It is used to check the current stack pointer
@@ -272,7 +266,6 @@ impl fmt::Display for ArgumentPurpose {
             Self::StructArgument(size) => return write!(f, "sarg({})", size),
             Self::StructReturn => "sret",
             Self::VMContext => "vmctx",
-            Self::SignatureId => "sigid",
             Self::StackLimit => "stack_limit",
         })
     }
@@ -285,7 +278,6 @@ impl FromStr for ArgumentPurpose {
             "normal" => Ok(Self::Normal),
             "sret" => Ok(Self::StructReturn),
             "vmctx" => Ok(Self::VMContext),
-            "sigid" => Ok(Self::SignatureId),
             "stack_limit" => Ok(Self::StackLimit),
             _ if s.starts_with("sarg(") => {
                 if !s.ends_with(")") {
@@ -392,7 +384,6 @@ mod tests {
             (ArgumentPurpose::Normal, "normal"),
             (ArgumentPurpose::StructReturn, "sret"),
             (ArgumentPurpose::VMContext, "vmctx"),
-            (ArgumentPurpose::SignatureId, "sigid"),
             (ArgumentPurpose::StackLimit, "stack_limit"),
             (ArgumentPurpose::StructArgument(42), "sarg(42)"),
         ];

cranelift/docs/ir.md

@@ -351,7 +351,7 @@ paramlist    : param { "," param }
 retlist      : paramlist
 param        : type [paramext] [paramspecial]
 paramext     : "uext" | "sext"
-paramspecial : "sarg" ( num ) | "sret" | "vmctx" | "sigid" | "stack_limit"
+paramspecial : "sarg" ( num ) | "sret" | "vmctx" | "stack_limit"
 callconv     : "fast" | "cold" | "system_v" | "windows_fastcall"
              | "wasmtime_system_v" | "wasmtime_fastcall"
              | "apple_aarch64" | "wasmtime_apple_aarch64"
@@ -366,12 +366,9 @@ system, a function's calling convention is only fully determined by a
 
 | Name      | Description |
 | ----------| ----------  |
+| sarg      | pointer to a struct argument of the given size |
 | sret      | pointer to a return value in memory |
-| link      | return address |
-| fp        | the initial value of the frame pointer |
-| csr       | callee-saved register |
 | vmctx     | VM context pointer, which may contain pointers to heaps etc. |
-| sigid     | signature id, for checking caller/callee signature compatibility |
 | stack_limit | limit value for the size of the stack |
 
 | Name      | Description |