X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=rts%2Fsm%2FGCThread.h;h=1b5c5d429182f897d3db4249c4f5a68468b109e5;hb=4f4dd70fd10ab13e41cb0f541bbfee2330d149da;hp=42d20bb2649050fd39b15a4d0d79c889db55a6a6;hpb=c1123a7dab90a0621db4f7f7e254614a6f3423a9;p=ghc-hetmet.git

diff --git a/rts/sm/GCThread.h b/rts/sm/GCThread.h
index 42d20bb..1b5c5d4 100644
--- a/rts/sm/GCThread.h
+++ b/rts/sm/GCThread.h
@@ -105,7 +105,7 @@ typedef struct step_workspace_ {
    GC thread object
 
    Every GC thread has one of these. It contains all the step specific
-   workspaces and other GC thread loacl information. At some later
+   workspaces and other GC thread local information. At some later
    point it maybe useful to move this other into the TLS store of the
    GC threads
    ------------------------------------------------------------------------- */
@@ -185,12 +185,20 @@ extern gc_thread **gc_threads;
 /* -----------------------------------------------------------------------------
    The gct variable is thread-local and points to the current thread's
    gc_thread structure.  It is heavily accessed, so we try to put gct
-   into a global register variable if possible.
+   into a global register variable if possible; if we don't have a
+   register then use gcc's __thread extension to create a thread-local
+   variable.
+
+   Even on x86 where registers are scarce, it is worthwhile using a
+   register variable here: I measured about a 2-5% slowdown with the
+   __thread version.
    -------------------------------------------------------------------------- */
 
 #define GLOBAL_REG_DECL(type,name,reg) register type name REG(reg);
 
-#if defined(REG_Base)
+#if defined(REG_Base) && !defined(i386_HOST_ARCH)
+// on i386, REG_Base is %ebx which is also used for PIC, so we don't
+// want to steal it
 
 GLOBAL_REG_DECL(gc_thread*, gct, REG_Base)
 #define DECLARE_GCT /* nothing */