Merge pull request rust-lang#243 from solson/magic_numbers

Get rid of magic numbers

Author: oli-obk

src/const_eval.rs

@@ -1,22 +1,20 @@
-use rustc::hir::def_id::DefId;
 use rustc::traits::Reveal;
-use rustc::ty::subst::Substs;
-use rustc::ty::{self, TyCtxt};
+use rustc::ty::{self, TyCtxt, Ty, Instance};
 
 use error::{EvalError, EvalResult};
 use lvalue::{Global, GlobalId, Lvalue};
+use value::PrimVal;
 use rustc_const_math::ConstInt;
 use eval_context::{EvalContext, StackPopCleanup};
 
-pub fn eval_body_as_integer<'a, 'tcx>(
+pub fn eval_body_as_primval<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
-    (def_id, substs): (DefId, &'tcx Substs<'tcx>),
-) -> EvalResult<'tcx, ConstInt> {
+    instance: Instance<'tcx>,
+) -> EvalResult<'tcx, (PrimVal, Ty<'tcx>)> {
     let limits = ::ResourceLimits::default();
     let mut ecx = EvalContext::new(tcx, limits);
-    let instance = ecx.resolve_associated_const(def_id, substs);
     let cid = GlobalId { instance, promoted: None };
-    if ecx.tcx.has_attr(def_id, "linkage") {
+    if ecx.tcx.has_attr(instance.def_id(), "linkage") {
         return Err(EvalError::NotConst("extern global".to_string()));
     }
 
@@ -28,7 +26,7 @@ pub fn eval_body_as_integer<'a, 'tcx>(
                 ty::ParamEnv::empty(Reveal::All),
                 mir.span);
         let cleanup = StackPopCleanup::MarkStatic(mutable);
-        let name = ty::tls::with(|tcx| tcx.item_path_str(def_id));
+        let name = ty::tls::with(|tcx| tcx.item_path_str(instance.def_id()));
         trace!("pushing stack frame for global: {}", name);
         ecx.push_stack_frame(
             instance,
@@ -41,11 +39,19 @@ pub fn eval_body_as_integer<'a, 'tcx>(
         while ecx.step()? {}
     }
     let value = ecx.globals.get(&cid).expect("global not cached").value;
-    let prim = ecx.value_to_primval(value, mir.return_ty)?.to_bytes()?;
+    Ok((ecx.value_to_primval(value, mir.return_ty)?, mir.return_ty))
+}
+
+pub fn eval_body_as_integer<'a, 'tcx>(
+    tcx: TyCtxt<'a, 'tcx, 'tcx>,
+    instance: Instance<'tcx>,
+) -> EvalResult<'tcx, ConstInt> {
+    let (prim, ty) = eval_body_as_primval(tcx, instance)?;
+    let prim = prim.to_bytes()?;
     use syntax::ast::{IntTy, UintTy};
     use rustc::ty::TypeVariants::*;
     use rustc_const_math::{ConstIsize, ConstUsize};
-    Ok(match mir.return_ty.sty {
+    Ok(match ty.sty {
         TyInt(IntTy::I8) => ConstInt::I8(prim as i128 as i8),
         TyInt(IntTy::I16) => ConstInt::I16(prim as i128 as i16),
         TyInt(IntTy::I32) => ConstInt::I32(prim as i128 as i32),

src/error.rs

@@ -69,6 +69,7 @@ pub enum EvalError<'tcx> {
     NeedsRfc(String),
     NotConst(String),
     ReadFromReturnPointer,
+    PathNotFound(Vec<String>),
 }
 
 pub type EvalResult<'tcx, T = ()> = Result<T, EvalError<'tcx>>;
@@ -175,6 +176,8 @@ impl<'tcx> Error for EvalError<'tcx> {
                 "this feature is not compatible with constant evaluation",
             ReadFromReturnPointer =>
                 "tried to read from the return pointer",
+            EvalError::PathNotFound(_) =>
+                "a path could not be resolved, maybe the crate is not loaded",
         }
     }
 
@@ -215,6 +218,8 @@ impl<'tcx> fmt::Display for EvalError<'tcx> {
                 write!(f, "\"{}\" needs an rfc before being allowed inside constants", msg),
             NotConst(ref msg) =>
                 write!(f, "Cannot evaluate within constants: \"{}\"", msg),
+            EvalError::PathNotFound(ref path) =>
+                write!(f, "Cannot find path {:?}", path),
             _ => write!(f, "{}", self.description()),
         }
     }

src/terminator/mod.rs

@@ -1,4 +1,4 @@
-use rustc::hir::def_id::DefId;
+use rustc::hir::def_id::{DefId, CRATE_DEF_INDEX};
 use rustc::mir;
 use rustc::ty::{self, TypeVariants, Ty};
 use rustc::ty::layout::Layout;
@@ -13,6 +13,8 @@ use memory::{MemoryPointer, TlsKey};
 use value::{PrimVal, Value};
 use rustc_data_structures::indexed_vec::Idx;
 
+use std::mem;
+
 mod drop;
 mod intrinsic;
 
@@ -853,12 +855,32 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
             "sysconf" => {
                 let name = self.value_to_primval(args[0], usize)?.to_u64()?;
                 trace!("sysconf() called with name {}", name);
-                let result = match name {
-                    30 => PrimVal::Bytes(4096), // _SC_PAGESIZE
-                    70 => PrimVal::from_i128(-1), // _SC_GETPW_R_SIZE_MAX
-                    _ => return Err(EvalError::Unimplemented(format!("Unimplemented sysconf name: {}", name)))
-                };
-                self.write_primval(dest, result, dest_ty)?;
+                // cache the sysconf integers via miri's global cache
+                let paths = &[
+                    (&["libc", "_SC_PAGESIZE"], PrimVal::Bytes(4096)),
+                    (&["libc", "_SC_GETPW_R_SIZE_MAX"], PrimVal::from_i128(-1)),
+                ];
+                let mut result = None;
+                for &(path, path_value) in paths {
+                    if let Ok(instance) = self.resolve_path(path) {
+                        use lvalue::GlobalId;
+                        let cid = GlobalId { instance, promoted: None };
+                        // compute global if not cached
+                        let val = match self.globals.get(&cid).map(|glob| glob.value) {
+                            Some(value) => self.value_to_primval(value, usize)?.to_u64()?,
+                            None => ::const_eval::eval_body_as_primval(self.tcx, instance)?.0.to_u64()?,
+                        };
+                        if val == name {
+                            result = Some(path_value);
+                            break;
+                        }
+                    }
+                }
+                if let Some(result) = result {
+                    self.write_primval(dest, result, dest_ty)?;
+                } else {
+                    return Err(EvalError::Unimplemented(format!("Unimplemented sysconf name: {}", name)));
+                }
             }
 
             // Hook pthread calls that go to the thread-local storage memory subsystem
@@ -933,4 +955,41 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
         self.goto_block(dest_block);
         Ok(())
     }
+
+    /// Get an instance for a path.
+    fn resolve_path(&self, path: &[&str]) -> EvalResult<'tcx, ty::Instance<'tcx>> {
+        let cstore = &self.tcx.sess.cstore;
+
+        let crates = cstore.crates();
+        crates.iter()
+            .find(|&&krate| cstore.crate_name(krate) == path[0])
+            .and_then(|krate| {
+                let krate = DefId {
+                    krate: *krate,
+                    index: CRATE_DEF_INDEX,
+                };
+                let mut items = cstore.item_children(krate, self.tcx.sess);
+                let mut path_it = path.iter().skip(1).peekable();
+
+                while let Some(segment) = path_it.next() {
+                    for item in &mem::replace(&mut items, vec![]) {
+                        if item.ident.name == *segment {
+                            if path_it.peek().is_none() {
+                                return Some(ty::Instance::mono(self.tcx, item.def.def_id()));
+                            }
+
+                            items = cstore.item_children(item.def.def_id(), self.tcx.sess);
+                            break;
+                        }
+                    }
+                }
+                None
+            })
+            .ok_or_else(|| {
+                let path = path.iter()
+                    .map(|&s| s.to_owned())
+                    .collect();
+                EvalError::PathNotFound(path)
+            })
+    }
 }