On Thu, 26 Jan 2012, Joe Perches wrote:
I'm trying to elide unnecessary initializations of
variable declarations when the variables are later
overwritten with a direct set.
I'm using:
$ cat multi_set.cocci
@@
type T;
identifier x;
expression y;
expression z;
@@
-T x = y;
This is much too general. You don't want to get rid of the assignment if
y is an arbitrary expression, such as a function call. You could just put
constant y. Or you could allow it to be eg a constant or an identifier,
but identifier seems unlikely enough that it is probably not worth
bothering with. I guess there could be a casted identifier. But in that
case, it seems unlikely that one would do that and then do nothing with
the value afterwards.
+T x;
...
x = z
$
This doesn't work appropriately when the elided variable
declaration is used in expression z.
You could try:
(
x = <+...x...+>
|
x = z
)
I would put ? in front of x = z, because there might be some execution
paths where x is not reassigned. Then there should be when != x on the
dots, and probably when strict as well, because you want the constraints
to be satisfied in error handling code as well.
julia
For instance, using current linux-kernel, the .cocci file above
generates this diff:
-----------------------
diff -u -p a/broadcom/bnx2x/bnx2x_stats.c b/broadcom/bnx2x/bnx2x_stats.c
--- a/broadcom/bnx2x/bnx2x_stats.c
+++ b/broadcom/bnx2x/bnx2x_stats.c
@@ -104,8 +104,7 @@ static void bnx2x_hw_stats_post(struct b
/* loader */
if (bp->executer_idx) {
int loader_idx = PMF_DMAE_C(bp);
- u32 opcode = bnx2x_dmae_opcode(bp, DMAE_SRC_PCI, DMAE_DST_GRC,
- true, DMAE_COMP_GRC);
+ u32 opcode;
opcode = bnx2x_dmae_opcode_clr_src_reset(opcode);
memset(dmae, 0, sizeof(struct dmae_command));
-----------------------
How can cocci be told to make expression z not allow use
of identifier x?
Is there a better way to write this?
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