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There is an optimization for reducing the number of instructions needed
to generate a `function_clause`. After the latest improvements of the
type optimization pass, that optimization is not always applied.
Here is an example:
-export([foo/3]).
foo(X, Y, Z) ->
bar(a, X, Y, Z).
bar(a, X, Y, Z) when is_tuple(X) ->
{X,Y,Z}.
Note that the compiler internally adds a clause to each function to
generate a `function_clause` exception. Thus:
bar(a, X, Y, Z) when is_tuple(X) ->
{X,Y,Z};
bar(A1, A2, A3, A4) ->
erlang:error(function_clause, [A1,A2,A3,A4]).
Optimizations will rewrite the code basically like this:
bar(_, X, Y, Z) when is_tuple(X) ->
{X,Y,Z};
bar(_, A2, A3, A4) ->
erlang:error(function_clause, [a,A2,A3,A4]).
Note the `a` as the first element of the list of arguments. It
will prevent the optimization of the `function_clause` exception.
The BEAM code for `bar/4` looks like this:
{function, bar, 4, 4}.
{label,3}.
{line,[{location,"t.erl",8}]}.
{func_info,{atom,t},{atom,bar},4}.
{label,4}.
{'%',{type_info,{x,0},{atom,a}}}.
{test,is_tuple,{f,5},[{x,1}]}.
{test_heap,4,4}.
{put_tuple2,{x,0},{list,[{x,1},{x,2},{x,3}]}}.
return.
{label,5}.
{test_heap,8,4}.
{put_list,{x,3},nil,{x,0}}.
{put_list,{x,2},{x,0},{x,0}}.
{put_list,{x,1},{x,0},{x,0}}.
{put_list,{atom,a},{x,0},{x,1}}.
{move,{atom,function_clause},{x,0}}.
{line,[{location,"t.erl",8}]}.
{call_ext,2,{extfunc,erlang,error,2}}.
The code after label 5 is the clause that generates the
`function_clause` exception.
This commit generalizes the optimization so that it can be applied for
this function:
{function, bar, 4, 4}.
{label,3}.
{line,[{location,"t.erl",8}]}.
{func_info,{atom,t},{atom,bar},4}.
{label,4}.
{'%',{type_info,{x,0},{atom,a}}}.
{test,is_tuple,{f,5},[{x,1}]}.
{test_heap,4,4}.
{put_tuple2,{x,0},{list,[{x,1},{x,2},{x,3}]}}.
return.
{label,5}.
{move,{atom,a},{x,0}}.
{jump,{f,3}}.
For this particular function, it would be safe to omit the
`move` instruction before the `{jump,{f,3}}` instruction, but
it would not be safe in general to omit `move` instructions.
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Speed up the compiler when compiling the idna package
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Fix problems compiling Scalaris
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* bjorn/compiler/beam_except:
beam_except: Eliminate unsafe function_clause translation
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Add ETS doc note about subtle iteration oddities
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The translation from `error(function_clause, Args)` to a jump
to the `func_info` label is not safe if there is a stack frame.
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Compilation of code similar the following would be very slow:
uts46_map(CP) when 0 =< CP, CP =< 44 -> '3';
uts46_map(CP) when 45 =< CP, CP =< 46 -> 'V';
uts46_map(CP) when 48 =< CP, CP =< 57 -> 'V';
%% More than 2500 similar lines follows.
.
.
.
The code is from from:
https://github.com/benoitc/erlang-idna/blob/3eb54ccbfa6fb917c0f4ca9197da337ad888ffe0/src/idna_mapping.erl#L6780
By using information about skippable blocks, the beam_ssa_dead
pass can be sped up to compile idna_mapping.erl about 10 times faster.
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It is never possible to merge a block ending in a switch with the
next block, so it is not necessary to call `beam_ssa:successors/1` in
that case. Avoiding the call slightly improves compilation speeds
for switches with many branches.
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To improve compilation times, beam_ssa_type keeps track of variables
that are only used once and don't keep types for those variables. As
currently implemented, it turns to be unsafe. Change it to only keep
track of variables that are only used in the terminator of the block
they are defined in.
https://bugs.erlang.org/browse/ERL-840
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If compilation failed, the name of the current function *and*
all previously compiled functions would be printed because
phase/4 was not tail-recursive.
https://bugs.erlang.org/browse/ERL-840
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* maint:
ssh: Internal refactor and ct:log -> ct:pal
ssh: Change unit in measurements
ssh: Invert ssh_bench
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* hans/ssh/cuddle_bench:
ssh: Internal refactor and ct:log -> ct:pal
ssh: Change unit in measurements
ssh: Invert ssh_bench
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* maint:
crypto: Reorg
crypto: Misc fixes: double time, calibrate once
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* hans/crypto/bench/OTP-15447:
crypto: Reorg
crypto: Misc fixes: double time, calibrate once
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* maint:
Updated OTP version
Prepare release
Include erlang-logo128.png in release
Enable setting custom application icon for Mac OS X through environment variable
Update to icon with better resolution
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* maint-21:
Updated OTP version
Prepare release
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Mnesia should always use the local context if available
OTP-15550
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Enable a way to change the application icon for Mac OS X in wx
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* siri/cover/searchable-uncovered/OTP-15542:
[cover] Make uncovered lines searchable in html output
[cover] Right-align number of hits in html output
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* john/compiler/trim-ignore-annos:
beam_trim: Ignore type annotations
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* john/compiler/misc-validator-fixes/ERL-832:
Make the beam_validator smarter again, again
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Reduce redundant moves and register shuffling
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Introduce optimizations of tail building
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* maint:
Pluggable distribution socket implementation for EI
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* rickard/ei-ext-maint/OTP-15442:
Pluggable distribution socket implementation for EI
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as it has been made more relevant with the introduction of
write_concurrency for ordered_set.
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The fix in f9ea85611faca82c7494449ddb8bcb1ef1d194cb didn't consider
that the tested register could be aliased.
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The type annotations inserted by beam_ssa_type and beam_ssa_bsm
would inadvertently disable stack trimming, as unknown instructions
are considered unsafe.
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Clarify ETS docs about table iterations
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Try to eliminate short blocks that starts with a phi node
and end in a return. For example:
Result = phi { Res1, 4 }, { literal true, 5 }
Ret = put_tuple literal ok, Result
ret Ret
The code in this block can be inserted at the end blocks 4 and
5. Thus, the following code can be inserted into block 4:
Ret:1 = put_tuple literal ok, Res1
ret Ret:1
And the following code into block 5:
Ret:2 = put_tuple literal ok, literal true
ret Ret:2
Which can be further simplified to:
ret literal {ok, true}
This transformation may lead to more code improvements, for example:
* Stack trimming
* Fewer test_heap instructions
* Smaller stack frames
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* ingela/inets/httpc-ipv6-brackets/OTP-15544:
inets: httpc - Do not use bracked addresses to gen_tcp or ssl calls
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* lukas/erts/scheduler-pollset-fixes/OTP-15538:
erts: Fix getting of poll events on linux >= 4.15.0
erts: Use reduction based polling for starved poll-set
erts: Fix pollset test cases
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* lukas/erts/fix_spawn_driver_early_close/OTP-15537:
erts: Fix too early close of spawn driver fd
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* lukas/erts/fix_inet_multitimer_cleanup/OTP-15536:
erts: Fix cleanup of the inet MultiTimer
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Apply type optimizations across local function calls
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This commit lets the type optimization pass work across functions,
tracking return and argument types to eliminate redundant tests.
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This serves as a base for the upcoming module-level type
optimization, but may come in handy for other passes like
beam_ssa_funs and beam_ssa_bsm that have their own ad-hoc
implementations.
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Consider this function and its corresponding BEAM code:
foo(Map, Key) ->
Val = case Map of
#{Key:=Val0} -> Val0;
_ -> default
end,
bar(1, 2, Val).
{label,2}.
{test,is_map,{f,3},[{x,0}]}.
{get_map_elements,{f,3},{x,0},{list,[{x,1},{x,0}]}}.
^^^^^
{jump,{f,4}}.
{label,3}.
{move,{atom,default},{x,0}}.
^^^^^
{label,4}.
{move,{integer,2},{x,1}}.
{move,{x,0},{x,2}}.
^^^^^
{move,{integer,1},{x,0}}.
{call_only,3,{f,6}}.
Note that the value of the variable `Val` will first be
placed in `{x,0}` and then moved to `{x,2}` where it needs
to be when calling the `bar/3` function.
The reason for the extra `move` instruction is that the
register allocator picks the lowest numbered available register
when choosing a register to put a variable in. In this case,
`{x,0}` will be chosen.
If we only could give a hint to the register allocator that
it would be better to put `Val` in `{x,2}`, the extra `move`
would disappear:
{label,2}.
{test,is_map,{f,3},[{x,0}]}.
{get_map_elements,{f,3},{x,0},{list,[{x,1},{x,2}]}}.
{jump,{f,4}}.
{label,3}.
{move,{atom,default},{x,2}}.
{label,4}.
{move,{integer,2},{x,1}}.
{move,{integer,1},{x,0}}.
{call_only,3,{f,6}}.
There already is an existing sub pass (`reserve_regs`) in
`beam_ssa_pre_codegen` that among things tries to give the register
allocator hints that some variables should be placed in specific
registers, if possible. However, the existing hinting mechanism is
limited, essentially only working within a single SSA block.
This commit extends the hinting mechanism, allowing hints to be passed
across SSA blocks, eliminating `move` instructions and register
shuffling in many places. (494 modules out of a sample of 1236 modules
were changed by this commit.)
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