* combine.c (expand_compound_operation) <ZERO_EXTRACT>: Add

[pf3gnuchains/gcc-fork.git] / gcc / rtl.def

diff --git a/gcc/rtl.def b/gcc/rtl.def
index c20f61b..7bee09b 100644 (file)
--- a/gcc/rtl.def
+++ b/gcc/rtl.def
@@ -587,10 +587,12 @@ DEF_RTL_EXPR(PARITY, "parity", "e", RTX_UNARY)
    If BITS_BIG_ENDIAN is defined, the first bit is the msb and
    operand 2 counts from the msb of the memory unit.
    Otherwise, the first bit is the lsb and operand 2 counts from
-   the lsb of the memory unit.  */
+   the lsb of the memory unit.
+   This kind of expression can not appear as an lvalue in RTL.  */
 DEF_RTL_EXPR(SIGN_EXTRACT, "sign_extract", "eee", RTX_BITFIELD_OPS)
 
-/* Similar for unsigned bit-field.  */
+/* Similar for unsigned bit-field.
+   But note!  This kind of expression _can_ appear as an lvalue.  */
 DEF_RTL_EXPR(ZERO_EXTRACT, "zero_extract", "eee", RTX_BITFIELD_OPS)
 
 /* For RISC machines.  These save memory when splitting insns.  */