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v3_codegen currently wraps a stack frame around each clause in
a function (unless the clause is simple without any 'case' or
other complex constructions).
Consider this function:
f({a,X}) ->
A = abs(X),
case A of
0 ->
{result,"0"};
_ ->
{result,integer_to_list(A)}
end;
f(_) ->
error.
The first clause needs a stack frame because there is a function
call to integer_to_list/1 not in the tail position. v3_codegen
currently wraps the entire first clause in stack frame.
We can delay the creation of the stack frame, and create a
stack frame in each arm of the 'case' (if needed):
f({a,X}) ->
A = abs(X),
case A of
0 ->
%% Don't create a stack frame here.
{result,"0"};
_ ->
%% Create a stack frame here.
{result,integer_to_list(A)}
end;
f(_) ->
error.
There are pros and cons of this approach.
The cons are that the code size may increase if there are many
'case' clauses and each needs its own stack frame. The allocation
instructions may also interfere with other optimizations, but
the new optimizations introduced in previous commits will mitigate
most of those issues.
The pros are the following:
* For some clauses in a 'case', there is no need to create any
stack frame at all.
* Often when moving an allocation instruction into a 'case' clause,
the slightly cheaper 'allocate' instruction can be used instead
of 'allocate_zero'. There is also the possibility that the
allocate instruction can be be combined with a 'test_heap'
instruction.
* Each stack frame for each arm of the 'case' will have exactly as
many slots as needed.
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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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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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* maint:
ssh: Update runtime dependencies of ssh
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Add syntax in try/catch to retrieve the stacktrace directly
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* bjorn/compiler/cover-v3_codegen:
v3_codegen: Simplify #k_guard_break{}
v3_codegen: Remove uncovered clause in bs_rename_ctx/4
Cover handling of #k_call{} in v3_codegen:bsm_rename_ctx/4
v3_codegen: Move guard_cg_list/6 to a more logical place
v3_codegen: Remove unnecessary clause for handling #cg_block{}
v3_codegen: Remove unnecessary adding of variable to set
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* hasse/stdlib/base64/OTP-14624:
stdlib: Add base64 benchmarks
stdlib: Do not check base64 input more than needed
stdlib: Minor optimization of base64
stdlib: Use binary_to_list in base64 when it is faster
stdlib: Optimize base64 functions
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* anders/diameter/typo/OTP-14805:
vsn -> 2.1.3
Update appup for 20.2
Fix doc typo
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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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bjorng/bjorn/compiler/fix-excessive-allocations/ERL-514
Avoid excessive stack frame allocation
OTP-14808
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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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Conflicts:
lib/ssl/src/ssl_cipher.erl
lib/ssl/src/ssl_handshake.erl
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* ingela/ssl/cipher-suites/OTP-14749:
ssl: Use maps for cipher suites internally
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This is a preparation for improvements to come in option handling and
support for TLS-1.3
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* peppe/common_test/auto_cleanup/OTP-13832:
Add tests and doc for the new remaining_test_procs function
Implement function that finds disposable test processes
Tag Common Test system processes using process dictionary
Add app name tag in process dictionary
OTP-13832
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* origin/raimo/ssl-dist-bench/OTP-14657:
Write SSL distribution benchmarks
Polish SSL distribution
Handle whitebox test message
Correct distribution doc
Use SNI when connecting
Use -ssl_dist_optfile options
Read in -ssl_dist_optfile to ETS
Facilitate test certs with common root
Stop checking DNS name for SNI
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* raimo/ssl-dist-optfile-backport/OTP-14657:
Use SNI when connecting
Use -ssl_dist_optfile options
Read in -ssl_dist_optfile to ETS
Facilitate test certs with common root
Stop checking DNS name for SNI
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* peppe/common_test/index_last_test/OTP-14281:
Show links to latest test run by using an html redirection file
OTP-14281
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