fixes, safeguards and docs for "compile-time arithmetics"

crsn/src/asm/instr/op.rs

@@ -65,4 +65,11 @@ impl OpTrait for Op {
 
         se
     }
+
+    fn is_compile_time_evaluable(&self) -> bool {
+         match &self.kind {
+            OpKind::BuiltIn(op) => op.is_compile_time_evaluable(),
+            OpKind::Ext(op) => op.is_compile_time_evaluable()
+        }
+    }
 }

crsn/src/asm/parse/parse_data.rs

@@ -3,7 +3,7 @@ use std::convert::TryFrom;
 
 use sexp::{Atom, Sexp, SourcePosition};
 
-use crate::asm::data::{DataDisp, Rd, RdData, reg, Wr, WrData, RdWr};
+use crate::asm::data::{DataDisp, Rd, RdData, reg, Wr, WrData, RdWr, Register};
 use crate::asm::data::literal::{ConstantName, Label, RegisterAlias, Value};
 use crate::asm::error::CrsnError;
 use crate::asm::parse::{ParserContext, parse_instructions};
@@ -75,6 +75,7 @@ pub fn parse_label_str(name: &str, pos: &SourcePosition) -> Result<Label, CrsnEr
 pub fn parse_data_disp(tok: Sexp, pcx: &ParserContext) -> Result<DataDisp, CrsnError> {
     // trace!("parse data: {:?}", tok);
     match tok {
+        // immediates are okay in const eval - no tests needed
         Sexp::Atom(Atom::I(val), _pos) => {
             Ok(DataDisp::Immediate(unsafe { std::mem::transmute(val) }))
         }
@@ -92,10 +93,12 @@ pub fn parse_data_disp(tok: Sexp, pcx: &ParserContext) -> Result<DataDisp, CrsnE
         }
         Sexp::List(list, pos) => {
             if let Some(Sexp::Atom(Atom::S(s), s_pos)) = list.first() {
+                // Const eval
+
                 let parsing_expr = pcx.state.borrow().parsing_expr;
 
                 if !s.starts_with('=') && !parsing_expr {
-                    return Err(CrsnError::Parse(format!("Invalid syntax, did you mean \"={}\"?", s).into(), s_pos.clone()));
+                    return Err(CrsnError::Parse(format!("Invalid syntax, did you mean \"={}\" (a compile-time expression)?", s).into(), s_pos.clone()));
                 }
 
                 // start expr parsing mode
@@ -116,6 +119,10 @@ pub fn parse_data_disp(tok: Sexp, pcx: &ParserContext) -> Result<DataDisp, CrsnE
 
                 let op = expr_ops.remove(0);
 
+                if !op.is_compile_time_evaluable() {
+                    return Err(CrsnError::Parse(format!("Instruction {} cannot be used in an expression!", op.to_sexp()).into(), pos.clone()));
+                }
+
                 let mut state_mut = pcx.state.borrow_mut();
                 state_mut.const_eval.clear_all();
 
@@ -144,12 +151,16 @@ pub fn parse_data_disp(tok: Sexp, pcx: &ParserContext) -> Result<DataDisp, CrsnE
 }
 
 /// Parse data disp from a string token (a &str is used so the string can be preprocessed)
-pub fn parse_data_disp_from_str(s: &str, pos: &SourcePosition, pcx: &ParserContext) -> Result<DataDisp, CrsnError> {
+fn parse_data_disp_from_str(s: &str, pos: &SourcePosition, pcx: &ParserContext) -> Result<DataDisp, CrsnError> {
     if s == "_" {
         return Ok(DataDisp::Discard);
     }
 
     if let Some(reference) = s.strip_prefix('@') {
+        if pcx.state.borrow().parsing_expr {
+            return Err(CrsnError::Parse("Object handles cannot be used in expressions!".into(), pos.clone()));
+        }
+
         /* extension constants (pre-defined handles) */
         for p in pcx.parsers {
             if let Some(val) = p.get_constant_value(reference) {
@@ -188,7 +199,7 @@ pub fn parse_data_disp_from_str(s: &str, pos: &SourcePosition, pcx: &ParserConte
             return Ok(DataDisp::Immediate(*val));
         }
 
-        /* register aliases */
+        /* register aliases - no need to check for const_eval, the aliases could never be defined */
         if let Some(val) = pstate.reg_aliases.get(s) {
             return Ok(DataDisp::Register(*val));
         } else if let Some(val) = pstate.global_reg_aliases.get(s) {
@@ -215,6 +226,14 @@ pub fn parse_data_disp_from_str(s: &str, pos: &SourcePosition, pcx: &ParserConte
             }
         }
 
+        if pcx.state.borrow().parsing_expr {
+            if s == "=result" {
+                return Ok(DataDisp::Register(Register::Gen(0)));
+            } else {
+                return Err(CrsnError::Parse("Registers cannot be used in expressions!".into(), pos.clone()));
+            }
+        }
+
         /* register */
         let reg = reg::parse_reg(&s, &pos)?;
 
@@ -231,39 +250,13 @@ pub fn parse_data_disp_from_str(s: &str, pos: &SourcePosition, pcx: &ParserConte
 
 /// Parse immediate value
 pub fn parse_value(tok: Sexp, pcx: &ParserContext) -> Result<(Value, SourcePosition), CrsnError> {
-    match tok {
-        Sexp::Atom(Atom::I(val), pos) => {
-            Ok((unsafe { std::mem::transmute(val) }, pos))
-        }
-        Sexp::Atom(Atom::U(val), pos) => {
-            Ok((val, pos))
-        }
-        Sexp::Atom(Atom::C(val), pos) => {
-            Ok((val as u64, pos))
-        }
-        Sexp::Atom(Atom::QS(_), pos) => {
-            Err(CrsnError::Parse("quoted string not expected here".into(), pos))
-        }
-        Sexp::Atom(Atom::F(val), pos) => {
-            Ok((unsafe { std::mem::transmute(val) }, pos))
-        }
-        Sexp::Atom(Atom::S(s), pos) => {
-            let pstate = pcx.state.borrow();
-            if let Some(val) = pstate.constants.get(&s) {
-                return Ok((*val, pos));
-            }
+    let pos = tok.pos().clone();
+    let parsed = parse_rd(tok, pcx)?;
 
-            /* extension constants */
-            for p in pcx.parsers {
-                if let Some(val) = p.get_constant_value(&s) {
-                    return Ok((val, pos));
-                }
-            }
-
-            Err(CrsnError::Parse(format!("unknown constant: {}", s).into(), pos))
-        }
-        Sexp::List(_, pos) => {
-            Err(CrsnError::Parse("expected a value".into(), pos))
+    match parsed {
+        Rd(RdData::Immediate(value)) => Ok((value, pos)),
+        _ => {
+            Err(CrsnError::Parse("expected an immediate value".into(), pos))
         }
     }
 }

crsn/src/asm/parse/parse_instr.rs

@@ -95,7 +95,7 @@ pub fn parse_instructions(items: impl Iterator<Item=Sexp>, pos: &SourcePosition,
 
         if parsing_expr {
             // hackity hack for const expr eval
-            arg_parser.prepend(atom_s("r0"));
+            arg_parser.prepend(atom_s("=result"));
         }
 
         if let Some(op) = parse_op(name.as_str(), arg_parser, &namepos)? {

crsn/src/builtin/exec.rs

@@ -204,6 +204,13 @@ impl OpTrait for BuiltinOp {
         Ok(res)
     }
 
+    fn is_compile_time_evaluable(&self) -> bool {
+        match self {
+            BuiltinOp::Load { .. } | BuiltinOp::LoadBits { .. } => true,
+            _ => false
+        }
+    }
+
     fn to_sexp(&self) -> Sexp {
         super::parse::to_sexp(self)
     }

crsn/src/module/mod.rs

@@ -48,6 +48,13 @@ pub trait OpTrait: Debug + Send + Sync + 'static {
 
     /// Turn into an S-expression that produces this instruction when parsed
     fn to_sexp(&self) -> Sexp;
+
+    /// Check if an operation is safe to use in compile-time arithmetics - has no side effects
+    /// outside the input and output registers (and flags), has the form (op Wr ...), and does not
+    /// use object handles or extension data.
+    fn is_compile_time_evaluable(&self) -> bool {
+        false
+    }
 }
 
 /// CRSN initializer object.