otp.git - Mirror of Erlang/OTP repository.

Age	Commit message (Collapse)	Author
2018-09-28	Fix rare bug in binary matching (again)	Björn Gustavsson
	2e40d8d1c51a attempted fix a bug in binary matching, but it only fixed the bug for the minimized test case. This commit removes the previous fix and fixes the bug in a more effective way. See the comments in the new code in `sys_core_bsm` for an explanation. This commit restores the optimizations in string.erl and dets_v9.erl that the previous fix disabled. I have not found any code where this commit will disable optimizations when they are actually safe. There are some changes to the code in ssl_cipher.erl in that some bs_start_match2 instruction did not reuse the binary register for the match context, but the delayed sub binary optimizations was never applied to the code in the first place. https://bugs.erlang.org/browse/ERL-689
2018-06-18	Update copyright year	Henrik Nord

2018-01-16	sys_core_bsm: Rearrange arguments to enable delayed sub binary creation	Björn Gustavsson
	Argument order can prevent the delayed sub binary creation. Here is an example directly from the Efficiency Guide: non_opt_eq([H\|T1], <<H,T2/binary>>) -> non_opt_eq(T1, T2); non_opt_eq([_\|_], <<_,_/binary>>) -> false; non_opt_eq([], <<>>) -> true. When compiling with the bin_opt_info option, there will be a suggestion to change the argument order. It turns out sys_core_bsm can itself change the order, not the order of the arguments of themselves, but the order in which the arguments are matched. Here is how it can be rewritten in pseudo Core Erlang code: non_opt_eq(Arg1, Arg2) -> case < Arg2,Arg1 > of < <<H1,T2/binary>>, [H2\|T1] > when H1 =:= H2 -> non_opt_eq(T1, T2); < <<_,T2/binary>ffff>, [_\|T1] > -> false; < <<>>, [] >> -> true end. When rewritten like this, the bs_start_match2 instruction will be the first instruction in the function and it will be possible to store the match context in the same register as the binary ({x,1} in this case) and to delay the creation of sub binaries. The switching of matching order also enables many other simplifications in sys_core_bsm, since there is no longer any need to pass the position of the pattern as an argument. We will update the Efficiency Guide in a separate branch before the release of OTP 21.
2017-12-08	Use the new syntax for retrieving stack traces	Björn Gustavsson

2017-06-07	Fix unsafe bit syntax matching optimization	Björn Gustavsson
	As part of sys_core_fold, variables involved in bit syntax matching would be annotated when it would be safe for a later pass to do the delayed sub-binary creation optimization. An implicit assumption regarding the annotation was that the code must not be further optimized. That assumption was broken in 05130e48555891, which introduced a fixpoint iteration (applying the optimizations until there were no more changes). That means that a variable could be annotated as safe for reusing the match context in one iteration, but a later iteration could rewrite the code in a way that would make the optimization unsafe. One way to fix this would be to clear all reuse_for_context annotations before each iteration. But that would be wasteful. Instead I chose to fix the problem by moving out the annotation code to a separate pass (sys_core_bsm) that is run later after all major optimizations of Core Erlang has been done.