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author | Björn Gustavsson <[email protected]> | 2018-05-09 12:56:48 +0200 |
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committer | Björn Gustavsson <[email protected]> | 2018-05-09 12:56:48 +0200 |
commit | b873e5cd6d78191d303c7c828ab7df7cd7fdf4d2 (patch) | |
tree | 87c975c0576f06f7439439ffb39bcc38f62c2b3c /system/doc/efficiency_guide/binaryhandling.xml | |
parent | 9be1ed4b7847044698563392b3d7b53565ea0873 (diff) | |
parent | 5e2f90735cfd78f353e549bf92bc8792ab1c6d34 (diff) | |
download | otp-b873e5cd6d78191d303c7c828ab7df7cd7fdf4d2.tar.gz otp-b873e5cd6d78191d303c7c828ab7df7cd7fdf4d2.tar.bz2 otp-b873e5cd6d78191d303c7c828ab7df7cd7fdf4d2.zip |
Merge branch 'bjorn/efficiency-guide'
* bjorn/efficiency-guide:
Remove obsolete example in Efficiency Guide
Diffstat (limited to 'system/doc/efficiency_guide/binaryhandling.xml')
-rw-r--r-- | system/doc/efficiency_guide/binaryhandling.xml | 82 |
1 files changed, 2 insertions, 80 deletions
diff --git a/system/doc/efficiency_guide/binaryhandling.xml b/system/doc/efficiency_guide/binaryhandling.xml index 19f40c9abe..d07ff1325f 100644 --- a/system/doc/efficiency_guide/binaryhandling.xml +++ b/system/doc/efficiency_guide/binaryhandling.xml @@ -357,25 +357,8 @@ all_but_zeroes_to_list(<<Byte,T/binary>>, Acc, Remaining) -> <c>Buffer</c> from a match context to a sub binary (or do nothing if <c>Buffer</c> is a binary already).</p> - <p>Before you begin to think that the compiler can optimize any binary - patterns, the following function cannot be optimized by the compiler - (currently, at least):</p> - - <code type="erl"><![CDATA[ -non_opt_eq([H|T1], <<H,T2/binary>>) -> - non_opt_eq(T1, T2); -non_opt_eq([_|_], <<_,_/binary>>) -> - false; -non_opt_eq([], <<>>) -> - true.]]></code> - - <p>It was mentioned earlier that the compiler can only delay creation of - sub binaries if it knows that the binary will not be shared. In this case, - the compiler cannot know.</p> - - <p>Soon it is shown how to rewrite <c>non_opt_eq/2</c> so that the delayed - sub binary optimization can be applied, and more importantly, it is shown - how you can find out whether your code can be optimized.</p> + <p>But in more complicated code, how can one know whether the + optimization is applied or not?</p> <section> <marker id="bin_opt_info"></marker> @@ -422,67 +405,6 @@ after_zero(<<>>) -> binary cannot be delayed, because it will be returned. The warning for the second clause says that a sub binary will not be created (yet).</p> - - <p>Let us revisit the earlier example of the code that could not - be optimized and find out why:</p> - - <code type="erl"><![CDATA[ -non_opt_eq([H|T1], <<H,T2/binary>>) -> - %% INFO: matching anything else but a plain variable to - %% the left of binary pattern will prevent delayed - %% sub binary optimization; - %% SUGGEST changing argument order - %% NOT OPTIMIZED: called function non_opt_eq/2 does not - %% begin with a suitable binary matching instruction - non_opt_eq(T1, T2); -non_opt_eq([_|_], <<_,_/binary>>) -> - false; -non_opt_eq([], <<>>) -> - true.]]></code> - - <p>The compiler emitted two warnings. The <c>INFO</c> warning refers - to the function <c>non_opt_eq/2</c> as a callee, indicating that any - function that call <c>non_opt_eq/2</c> cannot make delayed sub binary - optimization. There is also a suggestion to change argument order. - The second warning (that happens to refer to the same line) refers to - the construction of the sub binary itself.</p> - - <p>Soon another example will show the difference between the - <c>INFO</c> and <c>NOT OPTIMIZED</c> warnings somewhat clearer, but - let us first follow the suggestion to change argument order:</p> - - <code type="erl"><![CDATA[ -opt_eq(<<H,T1/binary>>, [H|T2]) -> - %% OPTIMIZED: creation of sub binary delayed - opt_eq(T1, T2); -opt_eq(<<_,_/binary>>, [_|_]) -> - false; -opt_eq(<<>>, []) -> - true.]]></code> - - <p>The compiler gives a warning for the following code fragment:</p> - - <code type="erl"><![CDATA[ -match_body([0|_], <<H,_/binary>>) -> - %% INFO: matching anything else but a plain variable to - %% the left of binary pattern will prevent delayed - %% sub binary optimization; - %% SUGGEST changing argument order - done; -...]]></code> - - <p>The warning means that <em>if</em> there is a call to <c>match_body/2</c> - (from another clause in <c>match_body/2</c> or another function), the - delayed sub binary optimization will not be possible. More warnings will - occur for any place where a sub binary is matched out at the end of and - passed as the second argument to <c>match_body/2</c>, for example:</p> - - <code type="erl"><![CDATA[ -match_head(List, <<_:10,Data/binary>>) -> - %% NOT OPTIMIZED: called function match_body/2 does not - %% begin with a suitable binary matching instruction - match_body(List, Data).]]></code> - </section> <section> |