/* -----------------------------------------------------------------------------
- * $Id: TailCalls.h,v 1.18 2005/01/28 12:55:54 simonmar Exp $
*
* (c) The GHC Team, 1998-1999
*
#if x86_64_HOST_ARCH
+/*
+ NOTE about __DISCARD__():
+
+ On x86_64 this is necessary to work around bugs in the register
+ variable support in gcc. Without the __DISCARD__() call, gcc will
+ silently throw away assignements to global register variables that
+ happen before the jump.
+
+ Here's the example:
+
+ extern void g(void);
+ static void f(void) {
+ R1 = g;
+ __DISCARD__()
+ goto *R1;
+ }
+
+ without the dummy function call, gcc throws away the assignment to R1
+ (gcc 3.4.3) gcc bug #20359.
+*/
+
#define JMP_(cont) \
{ \
- void *__target; \
- __target = (void *)(cont); \
- goto *__target; \
+ __DISCARD__(); \
+ goto *(void *)(cont); \
}
#endif /* x86_64_HOST_ARCH */