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When rewriting tuple matching of the first element of a tuple to an
is_tagged_tuple instruction, the get_tuple_element instruction that
fetches the tag will be left unless the register that is fetched is
subsequently killed.
We can do better than that. If the register is referenced in an
allocating instruction, but its value is never actually used, we
can do one of two things: if the value is known to be defined earlier
(using annotations added by beam_utils:anno_defs/1) the instruction
can be removed altogether; if not, it can be replaced with a
'move nil TagRegister' instruction.
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Use annotations added by beam_utils:anno_defs/1 to move more
allocations upwards in the instruction stream. That in turn
allows us to optimize away more 'move' instructions.
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To avoid having to call both is_killed/3 and is_not_used/3,
add usage/3 to answer both questions in one call.
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Add beam_utils:anno_defs/1 which will add an annotation to the
beginning of each block indicating which X registers that are
defined. Having that information can improve some optimizations.
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Add -MMD option to erlc
OTP-14830
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There are four uncovered lines in combine_heap_needs/2 and
combine_alloc_lists/2. There is no way to reach starting from
Erlang source code using the standard compiler. However, they
can be reached starting from BEAM assembly code, so we don't
want to remove them.
We could add a test case that covers the lines using assembly
code, but an easier solution is to rewrite the code in a more
generic way using sofs so that the code can be covered with
existing test cases.
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01835845579e9 fixed some problems, but introduced a bug where
is_not_used/3 would report that a register was not used when it
in fact was.
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758712d6294 changed the need_heap/2 function so that it stopped
using its second argument.
Remove the second argument from need_heap(), and update all callers
to similarly remove unused arguments.
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Add syntax in try/catch to retrieve the stacktrace directly
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It turns out that we don't need to keep track of locked
variables, because the locked variables are always the same
variables that will be alive after a #k_guard_break{}.
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Remove handling of #k_match{} in bsm_rename_ctx/4.
It can never be reached because bsm_rename_ctx/4 will never recurse
into a block that is not in the scope of a #k_protected{}, and
in a #k_protected{}, #k_match{} is not allowed.
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Put guard_cg_list/6 directly after guard_cg/5.
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The function guard_cg/5 handles constructs found within
the records #k_guard_clause{] and #k_protected{}.
Since #k_guard_clause{} can only contain a #k_protected{},
and #k_protected{} in turn cannot contain a #cg_block{},
the clause for handling #cg_block{} in guard_cg/5 is never
executed and can be removed.
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The variable being added will already be there (added by v3_kernel).
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When converting a comparison BIF (such as '=:=') to a test
instruction, run the other optimizations on the result.
When trying to combine is_eq_exact tests, handle the case
that is_eq_exact is followed by a jump instead of a label
to handle a test that has been newly converted from a BIF.
Taken together, those changes will coalesce more is_eq_exact
instructions into select_val instructions.
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A 'case' or 'if' that does not occur last in a function clause will
always force a stack frame. The reasoning behind this is that in most
uses of 'case' there will be a function call from within the
'case'. When there is a function call, the stack frame is needed both
to save the continuation pointer and to save any X registers that will
need to survive the call.
When there is no function call from a 'case', the resulting stack
frame is annoying. There will be register shuffling, and the existence
of the stack frame may thwart many optimizations (for example, in
beam_dead).
Therefore, add an extra pass to v3_codegen to avoid creating a
stack frame when not needed.
https://bugs.erlang.org/browse/ERL-514
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The compile option makedep_side_effect, erlc -MMD, instructs
the compiler to emit dependencies and continue to compile
as normal.
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v3_kernel could generate a #k_break{} with only one variable, even if
the preceding code and succeding code expected more than one value. It
happened to work anyway because the value returned from the break was
not actually used.
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We used to not care about the number of values returned from the
'after infinity' clause in a receive (because it could never be
executed). It is time to start caring because this will cause problem
when we will soon start to do some more aggressive optimizizations.
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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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X register 0 used to be mapped to a hardware register, and therefore
faster than the other registers. Because of that, the compiler
tried to use x(0) as much as possible as a temporary register.
That was changed a few releases ago. X register 0 is now placed
in the array of all X registers and has no special speed
advantage compared to the other registers.
Remove the code in the compiler that attempts to use x(0) as
much as possible. As a result, the following type of instruction
will be much less frequent:
{put_list,Src,{x,0},{x,0}}
Instead, the following type of instruction will be more frequent:
{put_list,Src,{x,X},{x,X}}
(Where X is an arbitrary X register.)
Update the runtime system to specialize that kind of put_list
instruction.
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The bs_context_to_binary instruction only allows a register operand.
v3_codegen has a test to ensure that the operand is a register.
That test is no longer necessary. There used to be a possibility
that optimizations in sys_core_fold and the inliner could change
the operand for bs_context_to_binary to a binary literal. Since
09112806c15a81b that can no longer happen, because no more
optimizations are run after the introduction of the
bs_context_to_binary instruction.
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This clause seems to have been introduced in cac51274eb9a.
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The clause that converted an iolist to a binary was never
executed.
Note that chunk/2 is called for all chunks in the
{extra_chunks,Chunks} option. This change will enforce that the
contents of each chunk must be a binary (as documented).
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beam_utils:bif_to_test/3 is supposed to never put a literal
operand as the first operand in is_eq_exact or is_ne_exact,
but 'nil' was not recognized as a literal.
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Place move S x0 instructions at the end of blocks
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The loader has a lot of fused instructions that include move S x0.
Placing them at the end of blocks makes it possible to take advantage
of this optimization more frequently.
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d8d07a7593d811 that added the to_dis option to the compiler no longer
works when merged to master. That is because of 79f28cfd8df1b7
that removed some unused code in erts_debug.
Fix this by adding a new function erts_debug:dis_to_file/2 and
use it from compile module where we have access to the filename
(in beam_listing we only have an opened file).
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Conflicts:
lib/compiler/src/beam_listing.erl
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* lukas/compiler/add_to_dis/OTP-14784:
compiler: Add +to_dis option that dumps loaded asm
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* maint:
Recognize 'deterministic' when given in a -compile() attribute
Conflicts:
lib/compiler/src/beam_asm.erl
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The compiler option 'deterministic' was only recognized when given
as an option to the compiler, not when it was specified in a
-compile() attribute in the source file.
https://bugs.erlang.org/browse/ERL-498
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Add some internal documentation about cerl_clauses
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The v3_life pass does not do enough to be worth being its own
pass. Essentially it does two things:
* Calculates life-time information starting from the annotations
that v3_kernel provides. That part can be moved into v3_codegen.
* Rewrites the Kernel Erlang records to similar plain tuples
(for example, #k_cons{hd=Hd,tl=Tl} is rewritten to {cons,Hd,Tl}).
That rewriting is not needed and can be eliminated.
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I recently tried to add some additional optimizations for
matching of maps, but found out that the inliner will need
some updates to be able to handle those optimizations.
Add lib/compiler/internal_doc/cerl-notes.md to document what
I've learned.
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If a type only has one clause and if the pattern is literal,
the matching can be done more efficiently by directly comparing
with the literal.
Example:
find(String, "") -> String;
find(String, <<>>) -> String;
find(String, SearchPattern) ->
.
.
.
Without this optimization, the relevant part of the code would look
this:
{test,bs_start_match2,{f,3},2,[{x,1},0],{x,2}}.
{test,bs_test_tail2,{f,4},[{x,2},0]}.
return.
{label,3}.
{test,is_nil,{f,4},[{x,1}]}.
return.
{label,4}.
.
.
.
That is, if {x,1} is a binary, a match context will be built to
test whether {x,1} is an empty binary.
With the optimization, the code will look this:
{test,is_eq_exact,{f,3},[{x,1},{literal,<<>>}]}.
return.
{label,3}.
{test,is_nil,{f,4},[{x,1}]}.
return.
{label,4}.
.
.
.
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Rewrite a catch expression like this:
catch side_effect(),
...
to:
try
side_effect()
catch
_:_ ->
ok
end,
...
A try/catch is more efficient since no stack trace will be built
when an exception occurs.
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Improve the receive optimization to be able to handle code
such as this:
Ref = make_ref(),
try
side_effect()
catch _:_ ->
ok
end,
receive
%% Clauses that all match Ref.
.
.
.
end
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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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Optimise size calculation for binary construction
OTP-14654
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* maint:
Fix incorrect internal consistency failure for binary matching code
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4c31fd0b9665 made the merging of match contexts stricter;
in fact, a little bit too strict.
Two match contexts with different number of slots would
be downgraded to the 'term' type. The correct way is to
keep the match context but set the number of slots to the
lowest number of slots of the two match contexts.
https://bugs.erlang.org/browse/ERL-490
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* siri/string-new-api: (28 commits)
hipe (test): Do not use deprecated functions in string(3)
dialyzer (test): Do not use deprecated functions in string(3)
eunit (test): Do not use deprecated functions in string(3)
system (test): Do not use deprecated functions in string(3)
system (test): Do not use deprecated functions in string(3)
mnesia (test): Do not use deprecated functions in string(3)
Deprecate old string functions
observer: Do not use deprecated functions in string(3)
common_test: Do not use deprecated functions in string(3)
eldap: Do not use deprecated functions in string(3)
et: Do not use deprecated functions in string(3)
os_mon: Do not use deprecated functions in string(3)
debugger: Do not use deprecated functions in string(3)
runtime_tools: Do not use deprecated functions in string(3)
asn1: Do not use deprecated functions in string(3)
compiler: Do not use deprecated functions in string(3)
sasl: Do not use deprecated functions in string(3)
reltool: Do not use deprecated functions in string(3)
kernel: Do not use deprecated functions in string(3)
hipe: Do not use deprecated functions in string(3)
...
Conflicts:
lib/eunit/src/eunit_lib.erl
lib/observer/src/crashdump_viewer.erl
lib/reltool/src/reltool_target.erl
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