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Since '=:=' is cheaper than '==', the compiler tries to replace
'==' with '=:=' if the result of comparison will be the same.
As an example:
V == {a,b}
can be rewritten to:
V =:= {a,b}
since the literal on the right side contains no numeric values
that '==' would compare differently to '=:='.
With the introduction of maps, we will need to take them into
account. Since the comparison of maps is planned to change in 18.0,
we will be very conservative and only do the optimization if
both keys and values are non-numeric.
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We must not convert map patterns to map expressions.
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In code such as:
case {a,Map} of
{a,#{}}=T ->
T
end
we must NOT rewrite a map pattern to a map expression like this:
case Map of
#{} ->
{a,#{}}
end
because the pattern '#{}' will match any map, but the expression
'#{}' will construct an empty map.
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core_lib:is_var_used/2 would not consider a variable used in the
value of a map pattern such as:
case Map of
#{key := <<42:N>>} -> ok
end
Here the variable 'N' would not be considered used.
It was assumed that there was no need to check map patterns at
all, since maps currently don't support variables in keys.
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* bjorn/compiler/map-in-record-bug/OTP-12402:
sys_core_fold: Correct optimization of 'case'
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When optimizing boolean expressions, it is not always possible
to find a number of live registers for a GC BIF that both preserves
all source registers that will be tested and at the same time
does not include registers that are not initialized.
As currently implemented, we have incomplete information about
the register calculated from the free variables. Some registers
are marked as "reserved". Reserved registers means that we don't
know anything about them; they may or may not be initialized.
As a conservative correction (suitable for a maintenance release), we
will abort the optimization if we find any reserved registers when
calculating the number of live registers. We will not attempt to
improve the information about the registers in this commit.
By examining the coverage when running the existing compiler test
suite we find that the optimization is aborted 15 times (before
adding any new test cases). To put that in perspective, the
optimization is successfully applied 4927 times, and aborted for
other reasons 547 times.
Reported-by: Ulf Norell
Reported-by: Anthony Ramine
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Old versions of the Erlang mode for Emacs used to indent try...catch
strangely - the first clause following the 'catch' would be indented
with one space less than the following clauses.
If we are to use the new Erlang mode when we add more clauses, they
would be indented with one space less than the preceding clauses.
That would look silly.
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The optimization of a 'case' statement could lead to incorrect
code that would cause an exception at run-time.
Here is an example to show how the optimization went wrong. Start
with the following code:
f({r,#{key:=Val},X}=S) ->
case S of
{r,_,_} ->
setelement(3, Val, S)
end.
(The record operations have already been translated to the
corresponding tuple operations.) The first step in case_opt/3 is
to substitute S to obtain:
f({r,#{key:=Val},X}=S) ->
case {r,#{key:=Val},X} of
{r,_,_} ->
setelement(3, Val, S)
end.
After that substitution the 'case' can be simplified to:
f({r,#{key:=Val},_}=S) ->
case #{key:=Val} of
NewVar ->
setelement(3, Val, S)
end.
That is the result from case_opt/3. Now eval_case/2 notices
that since there is only one clause left in the 'case', the
'case' can eliminated:
f({r,#{key:=Val},_}=S) ->
NewVar = #{key:=Val},
setelement(3, Val, S).
Since the map construction may have a side effect, it was not
eliminated, but assigned to a variable that is never used.
The problem is that '#{key:=Val}' is fine as a pattern, but in a
construction of a new map, the '=>' operator must be used. So the
map construction will fail, generating an exception.
As a conservative correction for a maintenance release, we will
abort the 'case' optimization if the substitution into the 'case'
expression is anything but data items (tuples, conses, or
literals) or variables.
Reported-by: Dmitry Aleksandrov
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This fixes a regression introduced in commit 805f9c89fc01220bc1bb0f27e1b68fd4eca688ba
The problem occured with map keys compiled with dialyzer option turned on.
In OTP 17, map keys needs to be literals.
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A module containing two named funs bearing the same name and arity could be
miscompiled.
Reported-by: Sam Chapin
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The scope is supposed to contain all variables that are currently
live. We need this information for certain optimizations to
avoid capturing a name (a name that is in the scope must be renamed;
for an example, see move_let_into_expr/2 or any function that calls
sub_subst_scope/1). We also use the scope to optimize sub_del_var/2
and sub_is_val/2.
When optimizing case expressions, the scope could be reset to an
empty list (because sub_new/0 was called instead of sub_new/1).
That could cause name capture if inlining was turned on.
As simple way to force this bug is to uncomment the
"-define(DEBUG, 1)." near the beginning of the file. Without this
correction, most files in the test suite fail to compile.
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* egil/fix-doc-links:
doc: Fix broken links in Installation Guide
doc: Fix broken links
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This ticket is about records in Erlang code, and when to check the
fields against the (optional) types given when defining records.
Dialyzer operates on the Erlang Core format, where there are no trace
of records. The fix implemented is a Real Hack:
Given the new option 'dialyzer' erl_expand_records marks the line
number of records in a way that is undone by v3_core, which in turn
inserts annotations that can be recognized by Dialyzer.
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The fallback to latin-1 encoding would not work if the invalid
UTF-8 characters occurred in a skipped branch in an -ifdef/-ifndef.
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* egil/fix-maps-pretty-layout/OTP-11947:
dialyzer: Add Maps type mismatch test
hipe,compiler: Fix Map literals pretty printing
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* egil/maps-compiler-coverage:
compiler: Do not evaluate map expressions with bad keys
compiler: Throw 'nomatch' on matching with bad binary keys
compiler: Variable keys are not allowed in Maps
compiler: Strengthen Maps warnings tests
compiler: map_pair cannot be a type clause in v3_life
compiler: Remove redudant code in v3_codegen
compiler: Test deep map structure
compiler: Remove redundant clause in v3_codegen
compiler: Cover #{ [] => Var } in testcase
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Map keys with large (non literal) binary keys must fail.
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Even if a binary key is written as a literal the compiler may
choose to make an expression. Emit a warning in those cases
and saying the case will not match.
This is a limitation in current implementation.
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No need to check for variables in Map keys.
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Increases coverage.
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Map pairs are encapsulated in a map.
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The pass sys_core_fold did not correctly handle non-matching patterns in code
such as:
0 = case <<>> of
<<>> -> 0;
a -> 1
end.
Function case_opt_lit/3 is rewritten in two passes to first remove any
non-matching clause and only then potentially remove the related patterns
in each clause.
Reported-by: Ulf Norell
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Multiple 'nil' cannot happen on instruction level.
Map keys are always unique with literals.
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Coverage removed by literals.
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Most dependencies introduced are exactly the dependencies to other
applications found by xref. That is, there might be real dependencies
missing. There might also be pure debug dependencies listed that
probably should be removed. Each application has to be manually
inspected in order to ensure that all real dependencies are listed.
All dependencies introduced are to application versions used in
OTP 17.0. This since the previously used version scheme wasn't
designed for this, and in order to minimize the work of introducing
the dependencies.
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Ensure all are "normal" versions according to the new version scheme
introduced in OTP 17.0
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* ks/cerl-type-fixes:
Restore the alphabetical order of Core Erlang records
Clean up the types of cerl
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* nox/maps-v3_core-lit_vars:
Properly collect variables in map expressions in v3_core
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* bjorn/compiler/utf8-warning/OTP-11791:
Don't fail compilation for modules that contain invalid UTF-8
epp: Make it possible to specify a default encoding
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The introduction of c_map{} and c_map_pair{} unnecessarily broke the
alphabetical order of Core Erlang records. They were probably placed
at the end of the file so as to use other records as types. There is
really no need for this since 'cerl' contains appropriate definitions
of types that can be used for this purpose.
While at it, a type declaration to the c_binary{} definition was added.
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The introduction of c_map and c_map_pair was not done properly. In
particular, the definition of ctype() and an important Edoc comment
were not up-to-date.
While at it,
- some more types were cleaned up and exported so as to be used
in core_parse.hrl and
- some obviously dead code was removed (the type/1 function does
not return 'nil', which in turn simplified a clause in the code
of meta_1/2).
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The default encoding for Erlang modules is now UTF-8, and the
compilation would fail if a module contained byte sequences that
are not valid UTF-8 sequences.
In a large project with say many hundreds of Erlang modules
with names of developers such as "Björn" or "Håkan" encoded in
latin-1, that could mean that many hundreds of files would need
to be modified just to get started testing OTP 17.
As a temporary measure to ease the transition, automatically
fall back to the latin-1 encoding with a warning for any module
that contains invalid byte sequences and for which no encoding
has been specified.
The intention is to remove this workaround in OTP 18 or 19.
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Reported-by: José Valim
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Core should not understand M#{}
Instead transform M#{} to
case _cor0 of
<_cor1>
when call 'erlang':'is_map'
(_cor0) ->
_cor1
( <_cor2> when 'true' ->
primop 'match_fail'
('badarg')
-| ['compiler_generated'] )
end
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