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The following Core Erlang code could not be loaded:
'f'/1 = fun (_1) ->
case <_1> of
<~{'foo':='foo'}~> when 'true' ->
_1
end
Loading would fail with the following message:
beam/beam_load.c(2314): Error loading function example:f/1: op i_get_map_element_hash p x a u x:
no specific operation found
https://bugs.erlang.org/browse/ERL-955
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A repeated test could be optimized away. Example:
bar(A) ->
if is_bitstring(A) ->
if is_binary(A) ->
binary;
true ->
bitstring
end;
true ->
other
end.
In the example, the `is_binary/1` test would be optimized away,
basically turning the example into:
bar(A) ->
if is_bitstring(A) ->
bitstring;
true ->
other
end.
Thanks user Marcus Kruse in the Elixir forum for noticing this bug.
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The type optimizer pass (`beam_ssa_type`) could make unsafe
negative inferences. That is, incorrectly infer that a variable
could *not* have a particular type.
This bug was found when adding another optimization. It is not
clear how write a failing test case without that added optimization.
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Simplify sys_core_fold by removing optimizations by removing the
optimizations that have been obsoleted by the preceding commits.
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Remove is_function/1,2 tests if that are known to never fail.
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`=:=` is faster than `==`, so when they would return the same result,
we want to replace `==` with `=:=`. There is currently such an optimization
in sys_core_fold, but the optimimization will be more effective if
done in beam_ssa_type because beam_ssa_type has better type information.
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* maint:
Eliminate compiler crash when compiling complex receive statements
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* bjorn/compiler/fix-receive-patch/ERL-950/OTP-15832:
Eliminate compiler crash when compiling complex receive statements
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* maint:
Fix non-terminating compilation
Fix compiler crash when funs were matched
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* bjorn/compiler/fix-freeze/ERL-948/OTP-15828:
Fix non-terminating compilation
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Improve optimization of redundant tests
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Make the swap instruction known to the compiler
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BEAM has had a `swap` instruction for several releases, but it was not
known to the compiler. The loader would translate a sequence of three
`move` instructions to the `swap` instructions, but only when it was
possible to determine that it would be safe.
By making `swap` known to the compiler, it can be applied in more
situations since it is easier for the compiler than for the loader
to ensure that the usage is safe, and the loader shenanigans can be
eliminated.
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Certain complex receive statements would result in an internal
compiler failure. That would happen when the compiler would fail
to find the common exit block following a receive. See the added
test case for an example.
https://bugs.erlang.org/browse/ERL-950
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The `beam_ssa_dead` pass is supposed to eliminate tests that are
determined to be redundant based on the outcome of a previous test.
For example, in the following example that repeats a guard test,
the second clause can never be executed:
foo(A) when A >= 42 -> one;
foo(A) when A >= 42 -> two;
foo(_) -> three.
`beam_ssa_dead` should have eliminated the second clause, but
didn't:
{test,is_ge,{f,5},[{x,0},{integer,42}]}.
{move,{atom,one},{x,0}}.
return.
{label,5}.
{test,is_ge,{f,6},[{x,0},{integer,42}]}.
{move,{atom,two},{x,0}}.
return.
{label,6}.
{move,{atom,three},{x,0}}.
return.
Correct the optimization of four different combinations of relational
operations that were too conservate. To ensure the correctness of the
optimization, also add an exahaustive test of all combinations of
relational operations with one variable and one literal. (Also remove
the weak and now redundant coverage tests in `beam_ssa_SUITE`.) With
this correction, the following code will be generated for the example:
{test,is_ge,{f,5},[{x,0},{integer,42}]}.
{move,{atom,one},{x,0}}.
return.
{label,5}.
{move,{atom,three},{x,0}}.
return.
Thanks to Dániel Szoboszlay (@dszoboszlay), whose talk at Code BEAM
STO 2019 made me aware of this missed opportunity for optimization.
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The compiler would not terminate while compiling the following code:
foo(<<N:32>>, Tuple, NewValue) ->
_ = element(N, Tuple),
setelement(N, Tuple, NewValue).
The type analysis pass would attempt to construct a huge list when
attempting analyse the type of `Tuple` after the call to
`setelement/3`.
https://bugs.erlang.org/browse/ERL-948
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The beam_except pass rewrites certain calls `erlang:error/{1,2}` to
use specialized instructions for common exceptions such as
`{badmatch,Term}`.
Move this optimization to `beam_ssa_pre_codegen` and `beam_ssa_codegen`.
The main reason for this change is that optimization passes operating
on SSA code are easier to maintain than optimization passes working
on BEAM code.
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Code such as the following would crash the compiler in OTP 22:
[some_atom = fun some_function/1]
The reason is that the fun would be copied (used both in the match
operation and as a value in the list), and the copy of the fun would
create two wrapper functions with the same name for calling
some_function/1. In OTP 21, the duplicate functions happened not to
cause any harm (one of the wrappers functions would be unused and
ultimately be removed by beam_clean). In OTP 22, the new beam_ssa_type
pass would be confused by the multiple definitions of the wrapper
function.
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The comment is outdated; trying to update the type of a dead value
will result in a type conflict, making this code unreachable.
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* john/compiler/fix-missing-match-reposition/ERL-923:
compiler: Propagate match context position on fail path
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`beam_asm` would encode `{literal,[]}`, `{literal,erlang}`, and
`{literal,42}` in a less efficient way than the equivalent values
`nil`, `{atom,erlang}`, and `{integer,42}`. That would increase the
size of BEAM files and could increase the loaded code size. It would
probably not harm performance, because `literal` was only used this
way in code that generates `badmatch` and `case_clause` exceptions.
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The core_parse.hrl can be used in applications with the
+warn_untyped_record compiler flag.
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* bjorn/compiler/cuddle-with-tests:
Verify the highest opcode for the r21 test suites
Add test_lib:highest_opcode/1
sys_core_fold: Simplify case_expand_var/2
beam_validator: Remove uncovered lines in lists_mod_return_type/3
Cover return type determination of lists functions
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Validation could fail when a function that never returned was used
in a try block (see attached test case). It's possible to solve
this without disabling the optimization as the generated code is
sound, but I'm not comfortable making such a large change this
close to the OTP 22 release.
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5239eb0c62a9 stopped storing patterns that a variable has matched.
The only tuples that are stored in the type database are tuples
that have been previously constructed.
Therefore, the code in sys_core_fold:case_expand_var/2 and friends
that converts a tuple pattern to a tuple construction can be simplified
to used the stored tuple directly.
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Don't bother infering the return types for lists function that
beam_ssa_type does not handle.
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* bjorn/hipe-compilation/OTP-15596:
HiPE: Don't fail the compilation for unimplemented instructions
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For reasons better explained in the source code, ssa_opt_float
skips optimizing inside guards but it failed to do so
consistently; while the pass never processed guard blocks, it was
still possible to erroneously defer error checking to a guard
block, crashing the compiler once it realized its state was
invalid.
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This ensures that unreachable branches are properly ignored on
repeated checks (although tuple type subtraction isn't complete
yet).
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Type subtraction never resulted in the 'none' type, even when it
was obvious that it should. Once that was fixed it became apparent
that inequality checks also fell into the same subtraction trap
that the type pass warned about in a comment.
This then led to another funny problem with select_val, consider
the following code:
{bif,'>=',{f,0},[{x,0},{integer,1}],{x,0}}.
{select_val,{x,0},{f,70},{list,[{atom,false},{f,69},
{atom,true},{f,68}]}}.
The validator knows that '>=' can only return a boolean, so once it
has subtracted 'false' and 'true' it killed the state because all
all valid branches had been taken, so validation would crash once
it tried to branch off the fail label.
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The current type conflict resolution works well for the example
case in the comment, but doesn't handle branched code properly,
consider the following:
{label,2}.
{test,is_tagged_tuple,{f,ignored},[{x,0},3,{atom,r}]}.
{allocate_zero,2,1}.
{move,{x,0},{y,0}}.
%% {y,0} is known to be {r, _, _} now.
{get_tuple_element,{x,0},2,{x,0}}.
{'try',{y,1},{f,3}}.
%% ... snip ...
{jump,{f,5}}.
{label,3}.
{try_case,{y,1}}.
%% {x,0} is the error class (an atom), {x,1} is the error term.
{test,is_eq_exact,{f,ignored},[{x,0},{y,0}]}.
%% ... since tuples and atoms can't meet, the type of {y,0} is
%% now {atom,[]} because the current code assumes the type
%% we're updating with.
{move,{x,1},{x,0}}.
{jump,{f,5}}.
{label,5}.
%% ... joining tuple (block 2) and atom (block 3) means 'term',
%% so the get_tuple_element instruction fails to validate
%% despite this being unrechable from block 3.
{test_heap,3,1}.
{get_tuple_element,{y,0},1,{x,1}}.
{put_tuple2,{x,0},{list,[{x,1},{x,0}]}}.
{deallocate,2}.
return.
This commit kills the state on type conflicts, making unreachable
instructions truly unreachable.
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While complex_test made certain branching instructions a lot easier
to read, we're still using `branch_state` for many others which is
hard to read and makes it impossible to "abort" branches on type
conflicts.
This commit replaces nearly all uses of `branch_state` with a
general branching mechanism, improving readability and paving the
way for proper type conflict resolution.
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The element type can not be extracted before the tuple type has
been updated.
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Move size=all binary clause pruning to v3_kernel
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Tune BEAM instructions for the new compiler (part 1)
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Optimize the beam_ssa_dead sub pass
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The advantage of moving it up is that it reduces the
size of the code emitted by v3_kernel, speeding
v3_kernel itself and beam_kernel_to_ssa pass.
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