Re: [Qemu-devel] [RFC PATCH v3 1/5] coccinelle: add a script to optimize tcg op using tcg_gen_extract()

[Julia Lawall]

Hello,

I don't think I have seen earlier versions of this script.  Are you
proposing it to be added to the kernel?  If so, it should be put in an
appropriate subdirectory of Coccinelle.

Overall, could you explain at a high level what it is intended to do?  It
uses rather heavily regular expressions and python code, so I wonder if
this is the best way to do it.

thanks,
julia

On Fri, 12 May 2017, Philippe Mathieu-Daudé wrote:

> If you have coccinelle installed you can apply this script using:
>
>     $ spatch \
>         --macro-file scripts/cocci-macro-file.h \
>         --dir target --in-place
>
> You can also use directly Peter Senna Tschudin docker image (easier):
>
>     $ 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
>
> Then verified that no manual touchups are required.
>
> The following thread was helpful while writing this script:
>
>     https://github.com/coccinelle/coccinelle/issues/86
>
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> ---
>  scripts/coccinelle/tcg_gen_extract.cocci | 71 
> ++++++++++++++++++++++++++++++++
>  1 file changed, 71 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..4823073005
> --- /dev/null
> +++ b/scripts/coccinelle/tcg_gen_extract.cocci
> @@ -0,0 +1,71 @@
> +// optimize TCG using extract op
> +//
> +// Copyright: (C) 2017 Philippe Mathieu-Daudé. GPLv2+.
> +// Confidence: High
> +// Options: --macro-file scripts/cocci-macro-file.h
> +//
> +// Nikunj A Dadhania optimization:
> +// http://lists.nongnu.org/archive/html/qemu-devel/2017-02/msg05211.html
> +// Aurelien Jarno optimization:
> +// http://lists.nongnu.org/archive/html/qemu-devel/2017-05/msg01466.html
> +// Coccinelle helpful issue:
> +// https://github.com/coccinelle/coccinelle/issues/86
> +
> address@hidden@ // match shri*+andi* pattern, calls script verify_len
> +identifier ret, arg;
> +constant ofs, len;
> +identifier shr_fn =~ "^tcg_gen_shri_";
> +identifier and_fn =~ "^tcg_gen_andi_";
> +position shr_p;
> +position and_p;
> +@@
> +(
> address@hidden(ret, arg, ofs);
> address@hidden(ret, ret, len);
> +)
> +
> address@hidden:python verify_len@
> +ret_s << match.ret;
> +len_s << match.len;
> +shr_s << match.shr_fn;
> +and_s << match.and_fn;
> +shr_p << match.shr_p;
> +extract_fn;
> +@@
> +print "candidate at %s:%s" % (shr_p[0].file, shr_p[0].line)
> +len_fn=len("tcg_gen_shri_")
> +shr_sz=shr_s[len_fn:]
> +and_sz=and_s[len_fn:]
> +# TODO: op_size shr<and allowed?
> +is_same_op_size = shr_sz == and_sz
> +print "  op_size: %s/%s (%s)" % (shr_sz, and_sz, "same" if is_same_op_size 
> else "DIFFERENT")
> +is_optimizable = False
> +if is_same_op_size:
> +    try: # only eval integer, no #define like 'SR_M' (cpp did this, else 
> some headers are missing).
> +        len_v = long(len_s.strip("UL"), 0)
> +        low_bits = 0
> +        while (len_v & (1 << low_bits)):
> +            low_bits += 1
> +        print "  low_bits:", low_bits, "(value: 0x%x)" % ((1 << low_bits) - 
> 1)
> +        print "  len: 0x%x" % len_v
> +        is_optimizable = ((1 << low_bits) - 1) == len_v # check low_bits
> +        print "  len_bits %s= low_bits" % ("=" if is_optimizable else "!")
> +        print "  candidate", "IS" if is_optimizable else "is NOT", 
> "optimizable"
> +        coccinelle.extract_fn = "tcg_gen_extract_" + and_sz
> +    except:
> +        print "  ERROR (check included headers?)"
> +    cocci.include_match(is_optimizable)
> +print
> +
> address@hidden depends on verify_len@
> +identifier match.ret, match.arg;
> +constant match.ofs, match.len;
> +identifier match.shr_fn;
> +identifier match.and_fn;
> +position match.shr_p;
> +position match.and_p;
> +identifier verify_len.extract_fn;
> +@@
> address@hidden(ret, arg, ofs);
> address@hidden(ret, ret, len);
> ++extract_fn(ret, arg, ofs, len);
> --
> 2.11.0
>