trans: Make names of internal symbols independent of CGU translation order.

Every codegen unit gets its own local counter for generating new symbol
names. This makes bitcode and object files reproducible at the binary
level even when incremental compilation is used.

3 files changed, 16 insertions, 8 deletions

diff --git a/src/librustc_trans/common.rs b/src/librustc_trans/common.rs
index 6ae5fc1657a..76b778fb61f 100644
--- a/src/librustc_trans/common.rs
+++ b/src/librustc_trans/common.rs
@@ -799,9 +799,7 @@ pub fn C_cstr(cx: &CrateContext, s: InternedString, null_terminated: bool) -> Va
                                                 s.as_ptr() as *const c_char,
                                                 s.len() as c_uint,
                                                 !null_terminated as Bool);
-
-        let gsym = token::gensym("str");
-        let sym = format!("str{}", gsym.0);
+        let sym = cx.generate_local_symbol_name("str");
         let g = declare::define_global(cx, &sym[..], val_ty(sc)).unwrap_or_else(||{
             bug!("symbol `{}` is already defined", sym);
         });
diff --git a/src/librustc_trans/consts.rs b/src/librustc_trans/consts.rs
index 15f7132e52d..0dc10aa7759 100644
--- a/src/librustc_trans/consts.rs
+++ b/src/librustc_trans/consts.rs
@@ -30,7 +30,6 @@ use rustc::hir;
 use std::ffi::{CStr, CString};
 use syntax::ast;
 use syntax::attr;
-use syntax::parse::token;
 
 pub fn ptrcast(val: ValueRef, ty: Type) -> ValueRef {
     unsafe {
@@ -44,10 +43,7 @@ pub fn addr_of_mut(ccx: &CrateContext,
                    kind: &str)
                     -> ValueRef {
     unsafe {
-        // FIXME: this totally needs a better name generation scheme, perhaps a simple global
-        // counter? Also most other uses of gensym in trans.
-        let gsym = token::gensym("_");
-        let name = format!("{}{}", kind, gsym.0);
+        let name = ccx.generate_local_symbol_name(kind);
         let gv = declare::define_global(ccx, &name[..], val_ty(cv)).unwrap_or_else(||{
             bug!("symbol `{}` is already defined", name);
         });
diff --git a/src/librustc_trans/context.rs b/src/librustc_trans/context.rs
index 1b67516a9e6..2a72d42296d 100644
--- a/src/librustc_trans/context.rs
+++ b/src/librustc_trans/context.rs
@@ -166,6 +166,9 @@ pub struct LocalCrateContext<'tcx> {
     type_of_depth: Cell<usize>,
 
     symbol_map: Rc<SymbolMap<'tcx>>,
+
+    /// A counter that is used for generating local symbol names
+    local_gen_sym_counter: Cell<usize>,
 }
 
 // Implement DepTrackingMapConfig for `trait_cache`
@@ -688,6 +691,7 @@ impl<'tcx> LocalCrateContext<'tcx> {
                 n_llvm_insns: Cell::new(0),
                 type_of_depth: Cell::new(0),
                 symbol_map: symbol_map,
+                local_gen_sym_counter: Cell::new(0),
             };
 
             let (int_type, opaque_vec_type, str_slice_ty, mut local_ccx) = {
@@ -1021,6 +1025,16 @@ impl<'b, 'tcx> CrateContext<'b, 'tcx> {
     pub fn empty_substs_for_def_id(&self, item_def_id: DefId) -> &'tcx Substs<'tcx> {
         self.shared().empty_substs_for_def_id(item_def_id)
     }
+
+    /// Generate a new symbol name with the given prefix. This symbol name must
+    /// only be used for definitions with `internal` or `private` linkage.
+    pub fn generate_local_symbol_name(&self, prefix: &str) -> String {
+        let idx = self.local().local_gen_sym_counter.get();
+        self.local().local_gen_sym_counter.set(idx + 1);
+        // Include a '.' character, so there can be no accidental conflicts with
+        // user defined names
+        format!("{}.{}", prefix, idx)
+    }
 }
 
 pub struct TypeOfDepthLock<'a, 'tcx: 'a>(&'a LocalCrateContext<'tcx>);