===================================================================
@@ -4680,8 +4680,9 @@
string. The instruction is not allowed to prefetch more than one byte
at a time since either string may end in the first byte and reading past
that may access an invalid page or segment and cause a fault. The
-effect of the instruction is to store a value in operand 0 whose sign
-indicates the result of the comparison.
+comparison terminates early if the fetched bytes are different or if
+they are equal to zero. The effect of the instruction is to store a
+value in operand 0 whose sign indicates the result of the comparison.
@cindex @code{cmpstr@var{m}} instruction pattern
@item @samp{cmpstr@var{m}}
@@ -4699,8 +4700,10 @@
order starting at the beginning of each string. The instruction is not allowed
to prefetch more than one byte at a time since either string may end in the
first byte and reading past that may access an invalid page or segment and
-cause a fault. The effect of the instruction is to store a value in operand 0
-whose sign indicates the result of the comparison.
+cause a fault. The comparison will terminate when the fetched bytes
+are different or if they are equal to zero. The effect of the
+instruction is to store a value in operand 0 whose sign indicates the
+result of the comparison.
@cindex @code{cmpmem@var{m}} instruction pattern
@item @samp{cmpmem@var{m}}
@@ -4708,9 +4711,10 @@
of @samp{cmpstr@var{m}}. The two memory blocks specified are compared
byte by byte in lexicographic order starting at the beginning of each
block. Unlike @samp{cmpstr@var{m}} the instruction can prefetch
-any bytes in the two memory blocks. The effect of the instruction is
-to store a value in operand 0 whose sign indicates the result of the
-comparison.
+any bytes in the two memory blocks. Also unlike @samp{cmpstr@var{m}}
+the comparison will not stop if both bytes are zero. The effect of
+the instruction is to store a value in operand 0 whose sign indicates
+the result of the comparison.
@cindex @code{strlen@var{m}} instruction pattern
@item @samp{strlen@var{m}}
===================================================================
@@ -3634,9 +3634,9 @@
}
/* Expand expression EXP, which is a call to the memcmp built-in function.
- Return NULL_RTX if we failed and the
- caller should emit a normal call, otherwise try to get the result in
- TARGET, if convenient (and in mode MODE, if that's convenient). */
+ Return NULL_RTX if we failed and the caller should emit a normal call,
+ otherwise try to get the result in TARGET, if convenient (and in mode
+ MODE, if that's convenient). */
static rtx
expand_builtin_memcmp (tree exp, ATTRIBUTE_UNUSED rtx target,
@@ -3648,7 +3648,10 @@
POINTER_TYPE, POINTER_TYPE, INTEGER_TYPE, VOID_TYPE))
return NULL_RTX;
-#if defined HAVE_cmpmemsi || defined HAVE_cmpstrnsi
+ /* Note: The cmpstrnsi pattern, if it exists, is not suitable for
+ implementing memcmp because it will stop if it encounters two
+ zero bytes. */
+#if defined HAVE_cmpmemsi
{
rtx arg1_rtx, arg2_rtx, arg3_rtx;
rtx result;
@@ -3663,16 +3666,9 @@
= get_pointer_alignment (arg2, BIGGEST_ALIGNMENT) / BITS_PER_UNIT;
enum machine_mode insn_mode;
-#ifdef HAVE_cmpmemsi
if (HAVE_cmpmemsi)
insn_mode = insn_data[(int) CODE_FOR_cmpmemsi].operand[0].mode;
else
-#endif
-#ifdef HAVE_cmpstrnsi
- if (HAVE_cmpstrnsi)
- insn_mode = insn_data[(int) CODE_FOR_cmpstrnsi].operand[0].mode;
- else
-#endif
return NULL_RTX;
/* If we don't have POINTER_TYPE, call the function. */
@@ -3697,18 +3693,10 @@
set_mem_size (arg2_rtx, INTVAL (arg3_rtx));
}
-#ifdef HAVE_cmpmemsi
if (HAVE_cmpmemsi)
insn = gen_cmpmemsi (result, arg1_rtx, arg2_rtx, arg3_rtx,
GEN_INT (MIN (arg1_align, arg2_align)));
else
-#endif
-#ifdef HAVE_cmpstrnsi
- if (HAVE_cmpstrnsi)
- insn = gen_cmpstrnsi (result, arg1_rtx, arg2_rtx, arg3_rtx,
- GEN_INT (MIN (arg1_align, arg2_align)));
- else
-#endif
gcc_unreachable ();
if (insn)
@@ -3734,7 +3722,7 @@
else
return convert_to_mode (mode, result, 0);
}
-#endif
+#endif /* HAVE_cmpmemsi. */
return NULL_RTX;
}