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Instructions that produce more than one result complicate
optimizations. get_list/3 is one of two instructions that
produce multiple results (get_map_elements/3 is the other).
Introduce the get_hd/2 and get_tl/2 instructions
that return the head and tail of a cons cell, respectively,
and use it internally in all optimization passes.
For efficiency, we still want to use get_list/3 if both
head and tail are used, so we will translate matching pairs
of get_hd and get_tl back to get_list instructions.
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Consider the following function:
function({function,Name,Arity,CLabel,Is0}, Lc0) ->
try
%% Optimize the code for the function.
catch
Class:Error:Stack ->
io:format("Function: ~w/~w\n", [Name,Arity]),
erlang:raise(Class, Error, Stack)
end.
The stacktrace is retrieved, but it is only used in the call
to erlang:raise/3. There is no need to build a stacktrace
in this function. We can avoid the building if we introduce
an instruction called raw_raise/3 that works exactly like
the erlang:raise/3 BIF except that its third argument must
be a raw stacktrace.
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This commit adds a new syntax for retrieving the stacktrace
without calling erlang:get_stacktrace/0. That allow us to
deprecate erlang:get_stacktrace/0 and ultimately remove it.
The problem with erlang:get_stacktrace/0 is that it can keep huge
terms in a process for an indefinite time after an exception. The
stacktrace can be huge after a 'function_clause' exception or a failed
call to a BIF or operator, because the arguments for the call will be
included in the stacktrace. For example:
1> catch abs(lists:seq(1, 1000)).
{'EXIT',{badarg,[{erlang,abs,
[[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20|...]],
[]},
{erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,674}]},
{erl_eval,expr,5,[{file,"erl_eval.erl"},{line,431}]},
{shell,exprs,7,[{file,"shell.erl"},{line,687}]},
{shell,eval_exprs,7,[{file,"shell.erl"},{line,642}]},
{shell,eval_loop,3,[{file,"shell.erl"},{line,627}]}]}}
2> erlang:get_stacktrace().
[{erlang,abs,
[[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,
23,24|...]],
[]},
{erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,674}]},
{erl_eval,expr,5,[{file,"erl_eval.erl"},{line,431}]},
{shell,exprs,7,[{file,"shell.erl"},{line,687}]},
{shell,eval_exprs,7,[{file,"shell.erl"},{line,642}]},
{shell,eval_loop,3,[{file,"shell.erl"},{line,627}]}]
3>
We can extend the syntax for clauses in try/catch to optionally bind
the stacktrace to a variable.
Here is an example using the current syntax:
try
Expr
catch C:E ->
Stk = erlang:get_stacktrace(),
.
.
.
In the new syntax, it would look like:
try
Expr
catch
C:E:Stk ->
.
.
.
Only a variable (not a pattern) is allowed in the stacktrace position,
to discourage matching of the stacktrace. (Matching would also be
expensive, because the raw format of the stacktrace would have to be
converted to the cooked form before matching.)
Note that:
try
Expr
catch E ->
.
.
.
is a shorthand for:
try
Expr
catch throw:E ->
.
.
.
If the stacktrace is to be retrieved for a throw, the 'throw:'
prefix must be explicitly included:
try
Expr
catch throw:E:Stk ->
.
.
.
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HiPE has had metadata for gc safety on it's temporaries for a while, but
it has never been enforced or even checked, so naturally several
gc-safety violations has slipped through.
A new pass, hipe_rtl_verify_gcsafe verifies gcsafety on optimised RTL
and is used when running the testsuite, and can be manually enabled with
+{hipe,[verify_gcsafe]}.
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If a try/catch is used to ignore the potential exception caused by some
expression with a side effect such as:
try
side_effect()
catch _Class:_Reason ->
ok
end,
.
.
.
the generated code will be wasteful:
try YReg TryLabel
%% call side_effect() here
try_end Yreg
jump GoodLabel
TryLabel:
try_case YReg
%% try_case has set up registers as follows:
%% x(0) -> error | exit | throw
%% x(1) -> reason
%% x(2) -> raw stack trace data
GoodLabel:
%% This code does not use any x registers.
There will be two code paths that both end up at GoodLabel, and
the try_case instruction will set up registers that are never used.
We can do better by replacing try_case with try_end to obtain this
code:
try YReg TryLabel
%% call side_effect() here
try_end Yreg
jump GoodLabel
TryLabel:
try_end YReg
GoodLabel:
The jump optimizer (beam_jump) can further optimize this code
like this:
try YReg TryLabel
%% call side_effect() here
TryLabel:
try_end YReg
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This is useful to generate shorter code for closures generated by
(fun F/A).
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This fixes a HiPE bug reported on erlang-questions on 2/11/2016.
The BEAM to ICode tranaslation of the bs_match_string instruction,
written long ago for binaries (i.e., with byte-sized strings), tried
to do a `clever' translation of even bit-sized strings using a HiPE
primop that took a `Size' argument expressed in *bytes*.
ICode is not really the place to do such a thing, and moreover there
is really no reason for the HiPE primop not to take a Size argument
expressed in *bits* instead. This commit changes the `Size' argument
to be in bits, postpones the translation of the bs_match_string primop
Fixed in a pair-programming/debugging session with @margnus1.
until RTL and does a proper translation using bit-sized quantities there.
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Expressions like <<0:(fun(X)->X end(anka))>> would fail with 'badarith'
in HiPE, but 'badarg' in BEAM.
hipe_beam_to_icode was attempting to optimise the amount of code
generated by letting the arithmetic error propagate instead of
catching it. However, since it was emitting a block to throw 'badarg' in
that case anyway, we can just reuse it to achieve just as compact code
that behaves exactly like BEAM.
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The unit size field was previously completely discarded when lowering
this instruction from BEAM to Icode.
This feature was previously missing and expressions such as <<0,
<<1:1>>/binary>> would succeed construction when compiled with HiPE.
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According to EEP-43 for maps, a 'badmap' exception should be
generated when an attempt is made to update non-map term such as:
<<>>#{a=>42}
That was not implemented in the OTP 17.
José Valim suggested that we should take the opportunity to
improve the errors coming from map operations:
http://erlang.org/pipermail/erlang-questions/2015-February/083588.html
This commit implement better errors from map operations similar
to his suggestion.
When a map update operation (Map#{...}) or a BIF that expects a map
is given a non-map term, the exception will be:
{badmap,Term}
This kind of exception is similar to the {badfun,Term} exception
from operations that expect a fun.
When a map operation requires a key that is not present in a map,
the following exception will be raised:
{badkey,Key}
José Valim suggested that the exception should be
{badkey,Key,Map}. We decided not to do that because the map
could potentially be huge and cause problems if the error
propagated through links to other processes.
For BIFs, it could be argued that the exceptions could be simply
'badmap' and 'badkey', because the bad map and bad key can be found in
the argument list for the BIF in the stack backtrace. However, for the
map update operation (Map#{...}), the bad map or bad key will not be
included in the stack backtrace, so that information must be included
in the exception reason itself. For consistency, the BIFs should raise
the same exceptions as update operation.
If more than one key is missing, it is undefined which of
keys that will be reported in the {badkey,Key} exception.
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Compiling single functions (as opposed to whole modules) to native
code complicates code management in HiPE. It would also vastly
complicate whole-module optimizations, such as returning multiple
return values instead of tuples within a module.
As a first step, remove the external interface for the single
compilation feature. In the future, there are many things that
could be restructured and simplified.
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Conflicts:
erts/aclocal.m4
erts/include/internal/ethread_header_config.h.in
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Pattern matching of floats with variable size (<<F:S/float>>) did
always fail. Judging from similar code for ints, this bug is simply
a typo.
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Introduce the line/1 instruction in the compiler and the BEAM
virtual machine. It will not yet be generated by the compiler and
will not actually carry any information.
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put_literal/2 was an experimental instruction added in R11 to
support literals, but before the R12 release support for literals
was implemented for all instruction, making the put_literal/2
instruction redundant. Although the beam_disasm module supports
dissambley of instructions in older releases, there is
no reason to have it support experimental instructions.
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bs_bits_to_bytes2/2 was an experimental instruction added in R11,
but was removed in R12. Although the beam_disasm and beam_validator
modules do support instructions in older releases, there is
no reason to have them support experimental instructions.
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The bug was introduced in d60f055697cfe8e7f94be4d291d49bb00a66bc52.
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* bg/opt-receive:
Test that gen_server:call/2,3 are fast even with a huge message queue
erts: Add tests for the receive optimization
Update primary bootstrap
erts: Implement recv_mark/1 and recv_set/1 for real
compiler tests: Cover the error handling code in beam_receive
compiler test: Test optimization of receive statements
Optimize selective receives in the presence of a large message queue
Introduce the new recv_mark/1 and recv_mark/1 instructions
Compile tests that communicate with R12 nodes with the r12 option
Move p_run/2 to test_lib
gen: Inline wait_resp_mon/2 to help the compiler optimize
OTP-8623 bg/opt-receive
reveive statements that can only read out a newly created reference are now
specially optimized so that it will execute in constant time regardless of
the number of messages in the receive queue for the process. That
optimization will benefit calls to gen_server:call(). (See gen:do_call/4
for an example of a receive statement that will be optimized.)
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Make the recv_mark/1 and recv_mark/1 instructions known to the
compiler and run-time system. For the moment, make the loader ignore
any occurrences of those instructions in BEAM files.
Also update hipe_beam_to_icode to ignore those instructions.
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