Add a howto for counting instructions

1 files changed, 53 insertions, 0 deletions

diff --git a/erts/emulator/internal_doc/CountingInstructions.md b/erts/emulator/internal_doc/CountingInstructions.md
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+++ b/erts/emulator/internal_doc/CountingInstructions.md
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+Counting Instructions
+=====================
+
+Here is an example that shows how to count how many times each
+instruction is executed:
+
+    $ (cd erts/emulator && make icount)
+     MAKE	icount
+    make[1]: Entering directory `/home/uabbgus/otp/erts/emulator'
+      .
+      .
+      .
+    make[1]: Leaving directory `/home/uabbgus/otp/erts/emulator'
+    $ cat t.erl
+    -module(t).
+    -compile([export_all,nowarn_export_all]).
+
+    count() ->
+        erts_debug:ic(fun benchmark/0).
+
+    benchmark() ->
+        %% Run dialyzer.
+        Root = code:root_dir(),
+        Wc1 = filename:join(Root, "lib/{kernel,stdlib}/ebin/*.beam"),
+        Wc2 = filename:join(Root, "erts/preloaded/ebin/*.beam"),
+        Files = filelib:wildcard(Wc1) ++ filelib:wildcard(Wc2),
+        Opts = [{analysis_type,plt_build},{files,Files},{get_warnings,true}],
+        dialyzer:run(Opts).
+    $ $ERL_TOP/bin/cerl -icount
+    Erlang/OTP 22 [RELEASE CANDIDATE 1] [erts-10.2.4] [source-ac0d451] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [hipe] [instruction-counting]
+
+    Eshell V10.2.4  (abort with ^G)
+    1> c(t).
+    {ok,t}
+    2> t:count().
+               0 badarg_j
+               0 badmatch_x
+               0 bs_add_jsstx
+               0 bs_context_to_binary_x
+                .
+                .
+                .
+       536461394 move_call_last_yfQ
+       552405176 allocate_tt
+       619920327 i_is_eq_exact_immed_frc
+       636419163 is_nonempty_list_allocate_frtt
+       641859278 i_get_tuple_element_xPx
+       678196718 move_return_c
+       786289914 is_tagged_tuple_frAa
+       865826424 i_call_f
+    Total: 20728870321
+    []
+    3>