Re: [Qemu-devel] [RFC PATCH v2] coccinelle: add a script to optimize tcg op using tcg_gen_extract()

[Philippe Mathieu-Daudé]

Ok I just understood Richard explanation, so this patch is WRONG and I 
need to get some real rest :(

On 05/10/2017 08:52 PM, Philippe Mathieu-Daudé wrote:
> Apply this script using:
>
> $ docker run -v `pwd`:`pwd` -w `pwd` petersenna/coccinelle \
>     --sp-file scripts/coccinelle/tcg_gen_extract.cocci \
>     --macro-file scripts/cocci-macro-file.h \
>     --dir target \
>     --in-place
>
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> ---
>
> This is a new version of the coccinelle script addressing Richard comments and
> trying to do it correctly. Also changed license to GPLv2+.
>
> The first rule matches, it calls a python2 script that basically checks the
> target_ulong is not overflowed: (msk << ofs) >> sizeof(target_ulong) == 0

WRONG

for ex tcg_gen_extract_i32():

    switch (len) {
    default:
        tcg_gen_shli_i32(ret, arg, 32 - len - ofs);
        tcg_gen_shri_i32(ret, ret, 32 - len);

'len' is not a mask as I used to think but is really a length.

> I think this is enough but if I'm wrong I can try to do as Richard suggested
> (counting the low bits).

Now I got it Richard!

> If this rule fails, there is no further processing, else the 3rd rule doing the
> patch is called.
> I couldn't figure still how to reuse args from rule2 in rule3 so it is mostly a
> copy of rule1.
>
> I also don't know yet how to process target-generic functions (ending _tl
> instead of _32 or _64) eventually the correct --include-option may resolve this.
>
> Applied it verified the ARM/M68K/PPC patches (2,3,5,7 from serie v1).
> The other archs weren't patched since they use _tl generic functions.
>
> I apologize for my python!
>
> Regards,
>
> Phil.
>
>  scripts/coccinelle/tcg_gen_extract.cocci | 61 ++++++++++++++++++++++++++++++++
>  1 file changed, 61 insertions(+)
>  create mode 100644 scripts/coccinelle/tcg_gen_extract.cocci
>
> diff --git a/scripts/coccinelle/tcg_gen_extract.cocci 
> b/scripts/coccinelle/tcg_gen_extract.cocci
> new file mode 100644
> index 0000000000..d75ef7d98c
> --- /dev/null
> +++ b/scripts/coccinelle/tcg_gen_extract.cocci
> @@ -0,0 +1,61 @@
> +// optimize TCG using extract op
> +//
> +// Copyright: (C) 2017 Philippe Mathieu-Daudé. GPLv2+.
> +// Confidence: Low
> +// Options: --macro-file scripts/cocci-macro-file.h
> +
> address@hidden@ // match shri*+andi* pattern, calls script check_len_correct
> +identifier ret, arg;
> +constant ofs, len;
> +identifier tcg_gen_shri =~ "^tcg_gen_shri_";
> +identifier tcg_gen_andi =~ "^tcg_gen_andi_";
> +position p;
> +@@
> +(
> +tcg_gen_shri(ret, arg, ofs);
> +tcg_gen_andi(ret, ret, len);@p
> +)
> +
> address@hidden:python check_len_correct@
> +ret_s << match.ret;
> +arg_s << match.arg;
> +ofs_s << match.ofs;
> +msk_s << match.len;
> +shr_s << match.tcg_gen_shri;
> +and_s << match.tcg_gen_andi;
> +@@
> +try:
> +    # only eval integer, no #define like 'SR_M'
> +    ofs = long(ofs_s, 0)
> +    msk = long(msk_s, 0)
> +    # get op_size: 32/64
> +    shr_sz = int(shr_s[-2:])
> +    and_sz = int(and_s[-2:])
> +    # op_size shr<and allowed
> +    # check overflow
> +    if shr_sz > and_sz or (msk << ofs) >> and_sz:

WRONG

> +        cocci.include_match(False) # no further process
> +except ValueError: # op_size: "tl" not handled yet
> +    cocci.include_match(False) # no further process
> +
> address@hidden depends on check_len_correct@ // ofs/len are valid, we can 
> replace
> +identifier ret, arg;
> +constant ofs, len;
> +@@
> +(
> +// from Nikunj A Dadhania comment:
> +// http://lists.nongnu.org/archive/html/qemu-devel/2017-02/msg05211.html
> +-tcg_gen_shri_tl(ret, arg, ofs);
> +-tcg_gen_andi_tl(ret, ret, len);
> ++tcg_gen_extract_tl(ret, arg, ofs, len);
> +|
> +// from Aurelien Jarno comment:
> +// http://lists.nongnu.org/archive/html/qemu-devel/2017-05/msg01466.html
> +-tcg_gen_shri_i32(ret, arg, ofs);
> +-tcg_gen_andi_i32(ret, ret, len);
> ++tcg_gen_extract_i32(ret, arg, ofs, len);
> +|
> +-tcg_gen_shri_i64(ret, arg, ofs);
> +-tcg_gen_andi_i64(ret, ret, len);
> ++tcg_gen_extract_i64(ret, arg, ofs, len);
> +)