[PATCH] parisc: Prevent using same register as soure and target in extru/shr

[Helge Deller <deller@gmx.de>]

In 2004 Randolph added the shr() assembly macro and noted that the
source and target register could not be the same.

I did not find any confindence in the docs for this restriction. Maybe
it's related that on PA2.0 the upper bits may be clobbered?

Anyway, add a compile-time check for it now.

Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/arch/parisc/include/asm/assembly.h b/arch/parisc/include/asm/assembly.h
index ea0cb318b13d..ca1a12ae5ee7 100644
--- a/arch/parisc/include/asm/assembly.h
+++ b/arch/parisc/include/asm/assembly.h
@@ -146,6 +146,9 @@
 	/* Shift Right - note the r and t can NOT be the same! */
 	.macro shr r, sa, t
 	extru \r, 31-(\sa), 32-(\sa), \t
+.ifc \r,\t
+        .error "Can not used the same register (\r) in shr/extru as source and target register."
+.endif
 	.endm

 	/* pa20w version of shift right */