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

[Philippe Mathieu-Daudé]

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