1 files changed, 98 insertions, 0 deletions
diff --git a/rts/sm/GCTDecl.h b/rts/sm/GCTDecl.h
new file mode 100644
index 0000000000..11795ca7fd
--- /dev/null
+++ b/rts/sm/GCTDecl.h
@@ -0,0 +1,98 @@
+/* -----------------------------------------------------------------------------
+ *
+ * (c) The GHC Team 1998-2009
+ *
+ * Documentation on the architecture of the Garbage Collector can be
+ * found in the online commentary:
+ * 
+ *   http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/GC
+ *
+ * ---------------------------------------------------------------------------*/
+
+#ifndef SM_GCTDECL_H
+#define SM_GCTDECL_H
+
+#include "BeginPrivate.h"
+
+/* -----------------------------------------------------------------------------
+   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; if we don't have a
+   register then use gcc's __thread extension to create a thread-local
+   variable.
+   -------------------------------------------------------------------------- */
+
+#if defined(THREADED_RTS)
+
+#define GLOBAL_REG_DECL(type,name,reg) register type name REG(reg);
+
+#define SET_GCT(to) gct = (to)
+
+
+
+#if (defined(i386_HOST_ARCH) && defined(linux_HOST_OS))
+// Using __thread is better than stealing a register on x86/Linux, because
+// we have too few registers available.  In my tests it was worth
+// about 5% in GC performance, but of course that might change as gcc
+// improves. -- SDM 2009/04/03
+//
+// We ought to do the same on MacOS X, but __thread is not
+// supported there yet (gcc 4.0.1).
+
+extern __thread gc_thread* gct;
+#define DECLARE_GCT __thread gc_thread* gct;
+
+
+#elif defined(sparc_HOST_ARCH)
+// On SPARC we can't pin gct to a register. Names like %l1 are just offsets
+//	into the register window, which change on each function call.
+//	
+//	There are eight global (non-window) registers, but they're used for other purposes.
+//	%g0     -- always zero
+//	%g1     -- volatile over function calls, used by the linker
+//	%g2-%g3 -- used as scratch regs by the C compiler (caller saves)
+//	%g4	-- volatile over function calls, used by the linker
+//	%g5-%g7	-- reserved by the OS
+
+extern __thread gc_thread* gct;
+#define DECLARE_GCT __thread gc_thread* gct;
+
+
+#elif 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 */
+
+
+#elif defined(REG_R1)
+
+GLOBAL_REG_DECL(gc_thread*, gct, REG_R1)
+#define DECLARE_GCT /* nothing */
+
+
+#elif defined(__GNUC__)
+
+extern __thread gc_thread* gct;
+#define DECLARE_GCT __thread gc_thread* gct;
+
+#else
+
+#error Cannot find a way to declare the thread-local gct
+
+#endif
+
+#else  // not the threaded RTS
+
+extern StgWord8 the_gc_thread[];
+
+#define gct ((gc_thread*)&the_gc_thread)
+#define SET_GCT(to) /*nothing*/
+#define DECLARE_GCT /*nothing*/
+
+#endif // THREADED_RTS
+
+#include "EndPrivate.h"
+
+#endif // SM_GCTDECL_H