librustc: Disable borrow check debugging even when rustc is compiled with -O0.

This improves -O0 compile times dramatically.

Makefile.in

@@ -122,6 +122,10 @@ endif
 ifdef TRACE
   CFG_RUSTC_FLAGS += -Z trace
 endif
+ifndef DEBUG_BORROWS
+  RUSTFLAGS_STAGE1 += -Z no-debug-borrows
+  RUSTFLAGS_STAGE2 += -Z no-debug-borrows
+endif
 
 # platform-specific auto-configuration
 include $(CFG_SRC_DIR)mk/platform.mk

src/librustc/driver/session.rs

@@ -66,6 +66,7 @@ pub static debug_info: uint = 1 << 20;
 pub static extra_debug_info: uint = 1 << 21;
 pub static statik: uint = 1 << 22;
 pub static print_link_args: uint = 1 << 23;
+pub static no_debug_borrows: uint = 1 << 24;
 
 pub fn debugging_opts_map() -> ~[(~str, ~str, uint)] {
     ~[(~"verbose", ~"in general, enable more debug printouts", verbose),
@@ -100,7 +101,10 @@ pub fn debugging_opts_map() -> ~[(~str, ~str, uint)] {
       extra_debug_info),
      (~"debug-info", ~"Produce debug info (experimental)", debug_info),
      (~"static", ~"Use or produce static libraries or binaries " +
-      "(experimental)", statik)
+      "(experimental)", statik),
+     (~"no-debug-borrows",
+      ~"do not show where borrow checks fail",
+      no_debug_borrows),
     ]
 }
 
@@ -141,7 +145,7 @@ pub struct options {
     parse_only: bool,
     no_trans: bool,
     debugging_opts: uint,
-    android_cross_path: Option<~str>
+    android_cross_path: Option<~str>,
 }
 
 pub struct crate_metadata {
@@ -271,6 +275,9 @@ pub impl Session_ {
     fn no_monomorphic_collapse(@self) -> bool {
         self.debugging_opt(no_monomorphic_collapse)
     }
+    fn debug_borrows(@self) -> bool {
+        self.opts.optimize == No && !self.debugging_opt(no_debug_borrows)
+    }
 
     fn str_of(@self, id: ast::ident) -> @~str {
         self.parse_sess.interner.get(id)
@@ -308,7 +315,7 @@ pub fn basic_options() -> @options {
         parse_only: false,
         no_trans: false,
         debugging_opts: 0u,
-        android_cross_path: None
+        android_cross_path: None,
     }
 }
 

src/librustc/middle/trans/write_guard.rs

@@ -74,7 +74,7 @@ pub fn return_to_mut(mut bcx: block,
     let bits_val =
         Load(bcx, bits_val_ref);
 
-    if bcx.tcx().sess.opts.optimize == session::No {
+    if bcx.tcx().sess.debug_borrows() {
         bcx = callee::trans_lang_call(
             bcx,
             bcx.tcx().lang_items.unrecord_borrow_fn(),
@@ -160,7 +160,7 @@ fn root(datum: &Datum,
                 ],
                 expr::SaveIn(scratch_bits.val));
 
-            if bcx.tcx().sess.opts.optimize == session::No {
+            if bcx.tcx().sess.debug_borrows() {
                 bcx = callee::trans_lang_call(
                     bcx,
                     bcx.tcx().lang_items.record_borrow_fn(),