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When an exception is handled, the stack will be scanned. Therefore
all Y registers must be initialized.
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beam_utils:is_killed/3 could incorrectly indicate that a
register was killed.
The previous fix is 5da6b91ecab6c.
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Rewrite a call of a literal external fun to a direct call
OTP-15044
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Rewrite calls such as:
(fun erlang:abs/1)(-42)
to:
erlang:abs(-42)
While we are at it, also add rewriting of apply/2 with a fixed
number of arguments to a direct call of the fun. For example:
apply(F, [A,B])
would be rewritten to:
F(A, B)
https://bugs.erlang.org/browse/ERL-614
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Help us find more compiler bugs.
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sys_core_fold would crash when attempting to optimize this code:
t() when (#{})#{}->
c.
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* 'map-get-bif' of git://github.com/michalmuskala/otp:
Introduce map_get guard-safe function
OTP-15037
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Rationale
Today all compound data types except for maps can be deconstructed in guards.
For tuples we have `element/2` and for lists `hd/1` and `tl/1`. Maps are
completely opaque to guards. This means matching on maps can't be
abstracted into macros, which is often done with repetitive guards. It
also means that maps have to be always selected whole from ETS tables,
even when only one field would be enough, which creates a potential
efficiency issue.
This PR introduces an `erlang:map_get/2` guard-safe function that allows
extracting a map field in guard. An alternative to this function would be
to introduce the syntax for extracting a value from a map that was planned
in the original EEP: `Map#{Key}`.
Even outside of guards, since this function is a guard-BIF it is more
efficient than using `maps:get/2` (since it does not need to set up the
stack), and more convenient from pattern matching on the map (compare:
`#{key := Value} = Map, Value` to `map_get(key, Map)`).
Performance considerations
A common concern against adding this function is the notion that "guards
have to be fast" and ideally execute in constant time. While there are
some counterexamples (`length/1`), what is more important is the fact
that adding those functions does not change in any way the time
complexity of pattern matching - it's already possible to match on map
fields today directly in patterns - adding this ability to guards will
niether slow down or speed up the execution, it will only make certain
programs more convenient to write.
This first version is very naive and does not perform any optimizations.
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Keys in map patterns are input variables, not pattern variables.
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1ee21858db7e strengenthed validatation of GC instructions, but
forgot the following instructions:
bs_start_match2/5
bs_get_binary2/7
bs_get_float2/7
bs_get_integer2/7
bs_get_utf8/5
bs_get_utf16/5
bs_get_utf32/5
bs_skip_utf8/4
bs_skip_utf16/4
bs_skip_utf32/4
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Waiting messages for a process may be stored in a queue
outside of any heap or heap fragment belonging to the process.
This is an optimization added in a recent major release to
avoid garbage collection messages again and again if there
is a long message queue.
Until such message has been matched and accepted by
the remove_message/0 instruction, the message must not be
included in the root set for a garbage collection, as that
would corrupt the message. The loop_rec/2 instruction explicitly
turns off garbage collection of the process as long messages
are being matched.
However, if the compiler were to put references to a message
outside of the heap in an Y register (on the stack) and there
happened to be a GC when the process had been scheduled out,
the message would be corrupted and the runtime system would
crash sooner or later.
To ensure that doesn't happen, teach beam_validator to check
for references on the stack to messages outside of the heap.
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Fix unsafe optimization of record test
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beam_record would make an unsafe optimization for the
not_used_p/4 function added to beam_utils_SUITE in this
commit. The bug is in beam_utils, which would falsely
report that {x,4} was unused when it in fact was used.
The bug was in the function not_used/1. The purpose of
not_used/1 is to return a 'not_used' result unless the
actual result is 'used'. Unfortunately it was not
implemented in that way. It would let a 'transparent'
result slip through, which the caller in this case would
convert to 'killed' (because the register was killed on
all other paths).
Reported-by: Richard Carlsson
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Compile external fun expressions to literals
OTP-15003
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bjorng/bjorn/compiler/fix-atom-leak/ERL-563/OTP-14968
Stop the compiler from overflowing the atom table
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The expressions fun M:F/A, when all elements are literals are also
treated as a literal. Since they have consistent representation and
don't depend on the code currently loaded in the VM, this is safe.
This can provide significant performance improvements in code using such
functions extensively - a full function call to erlang:make_fun/3 is
replaced by a single move instruction and no register shuffling or
saving registers to stack is necessary. Additionally, compound data
types that contain such external functions as elements can be treated as
literals too.
The commit also changes the representation of external funs to be a
valid Erlang syntax and adds support for literal external funs to core
Erlang.
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Use integer variable names instead of atoms in v3_core, sys_core_fold,
and v3_kernel to avoid overflowing the atom table.
It is a deliberate design decision to calculate the first free integer
variable name (in sys_core_fold and v3_kernel) instead of somehow
passing it from one pass to another. I don't want that kind of
dependency between compiler passes. Also note that the next free
variable name is not easily available after running the inliner.
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The way variables created by make_template() are used, it is necessary
that the names are unique in the entire function. This has not
happened to cause any problems in the past because all other compiler
passes created atom variable names, not integer variable names. If
other passes start to create integer variable names, this bug is
exposed.
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During compilation, the bs_save2 and bs_restore2 instructions contain a match
context reference. That reference is the variable name that holds the match context.
beam_clean assumes that the reference always is an atom, which is not a safe assumption
since integers are legal variable names in Core Erlang.
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When a generator in a list comprehension was given some
other term than a list, the wrong line could be pointed
out in the exception. Here is an example:
bad_generator() ->
[I || %%This line would be pointed out.
I <- not_a_list].
https://bugs.erlang.org/browse/ERL-572
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A literal negative size in binary construction would cause a crash.
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The missing support for renumbering labels in recv_mark
and recv_set did not seem to cause any problems, probably because
the insructions are introduced late and their labels would keep
their numbers. But it there will definitely be a problem if the
recv_mark and recv_set instructions would be introduced much earlier.
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For unclear reasons, v3_kernel attempts to guarantee that #k_try{}
always has at least one return value, even if it will never be
used. I said "attempts", because the handler block that is executed
when an exception is caught does not have the same guarantee. That
means that if an exception is thrown, the return value will not
actually be set.
In practice, however, this is not a problem for the existing code
generator (v3_codegen). The generated code will still be safe.
If we are to rewrite the code generator to generate an SSA-based
intermediate format, this inconsistency *will* cause problems
when creating phi nodes.
While at it, also remove an unecessary creation of new variables
in generation of #k_try_enter{}.
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* hasse/dialyzer/extra-range/OTP-14970:
ssl: Correct some specs
os_mon: Correct a spec
Fix broken spec in beam_asm
Dialyzer should not throw away spec information because of overspec
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Refactor and fix minor bugs in beam_type
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Fix beam_utils bugs that could cause problems in the future
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Make sure to kill all dependencies when a register is killed. For example,
in the following code, when the type information for {x,0} is killed in
the last instruction, there will still be type information for {x,1} referring
to {x,0}:
{get_tuple_element,{x,0},0,{x,1}}.
{test,is_eq_exact,{f,5},[{x,1},{atom,tag}]}.
{get_tuple_element,{x,0},1,{x,2}}.
{get_tuple_element,{x,0},2,{x,0}}.
This does not seems to have caused any problems in the past, but it may
cause problems in the future with a register allocator that reuses register
more aggressively.
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The function tdb_update/2 is problematic. It does not distinguish
between assigning a register with a new value and updating information
about a register that is used a as source in a test instruction.
That was not a problem in practice when there were very few types,
but bugs started to be noticed as more types were added. (For example,
when a register was overwritten with a new value, the type for the
old value stored in the same register could linger in some cases.)
Introduce separate functions tdb_store/3 and tdb_meet/3 for assigning
a new value to a register and for updating type information for a
register referenced as as source, respectively. Also stricten
verification of the types that gets stored into the type database.
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In the following code:
{get_tuple_element,{x,0},0,{x,1}}.
{put_tuple,2,{x,1}}.
{put,{atom,badmap}}.
{put,{x,0}}.
{move,{x,1},{x,0}}.
beam_block would move the get_tuple_element/3 instruction and eliminate the
move/2 instruction:
{put_tuple,2,{x,1}}.
{put,{atom,badmap}}.
{put,{x,0}}.
{get_tuple_element,{x,0},0,{x,0}}.
That is not correct, since the result of the tuple building in {x,1} is
now ignored.
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live_opt_block/4 could overestimate the number of live
registers for a GC BIF and trigger an assertion. This does not
seem to be a problem when generating code using v3_codegen,
but only when using a new experimental code generator, therefore
there is no need include this correction in maint.
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is_killed/3 and is_killed_at/3 could return 'true' even if the
register was referenced by an allocation instruction. Somehow, that
does not seem to have caused any problems yet.
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Every catch or try/catch must use a lower Y register number than any
enclosing catch or try/catch. That will ensure that when the stack
is scanned when an exception occurs, the innermost try/catch tag is
found first.
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1a029efd1ad47f started to run the beam_block pass a second time,
but it did not attempt to combine adjacent blocks.
Combining adjacent blocks leads to many more opportunities for
optimizations.
After doing some diffing in generated code, it turns out that
there is no benefit for beam_split to split out line instructions
from blocks. It seems that the only reason it was done was to
slightly simplify the implementation of the no_line_info option
in beam_clean.
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As a preparation for combining blocks before running beam_block
for the second time, disable CSE for floating point operations
because it will generate invalid code.
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* maint:
Check that the stack is initialized when an exception may occur
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The more aggressive optimizations of 'allocate_zero' introduced
in cb6fc15c35c7e could produce unsafe code such as the following:
{allocate,0,1}.
{bif,element,{f,0},[{integer,1},{x,0}],{x,0}}.
The code is not safe because if element/2 fails, the runtime
system may scan the stack and find garbage that looks like a
catch tag, and would most probably crash.
Fix the problem by making beam_utils:is_killed/3 be more conservative
when asked whether a Y register will be killed.
Also fix an unsafe move upwards of an allocation instruction
in beam_block.
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Strengthen beam_validator to check that the stack is initialized
when an instruction with an {f,0} operand is executed.
For example, the following code sequence:
{allocate,0,1}.
{bif,element,{f,0},[{integer,1},{x,0}],{x,0}}.
should not be accepted because the stack may be scanned if
element/2 fails. That could cause a crash or other undefined
behavior if garbage on the stack looks like a catch tag.
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Eliminate get_list/3 internally in the compiler
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Fix incorrect handling of floating point instructions
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* maint:
Fix incorrect type interference of integer ranges
Conflicts:
lib/compiler/src/beam_type.erl
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1a029efd1ad47f started to run the beam_block pass a second time.
Since it is run after introduction of the optimized floating point
instructions, it must handle those instructions correctly.
In particular, it must be careful when hoisting allocation
instructions. For example, the following code:
{test_heap,{alloc,[{words,0},{floats,1}]},5}.
.
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.
{fmove,{fr,2},{x,0}}.
{allocate_zero,1,4}.
must not be rewritten to:
{test_heap,{alloc,[{words,0},{floats,1}]},5}.
.
.
.
{allocate_zero,1,4}.
{fmove,{fr,2},{x,0}}.
because beam_validator will not consider it safe. (The code may
actually be safe depending on what the code between the two allocation
instructions do.)
https://bugs.erlang.org/browse/ERL-555
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Instructions that produce more than one result complicate
optimizations. get_list/3 is one of two instructions that
produce multiple results (get_map_elements/3 is the other).
Introduce the get_hd/2 and get_tl/2 instructions
that return the head and tail of a cons cell, respectively,
and use it internally in all optimization passes.
For efficiency, we still want to use get_list/3 if both
head and tail are used, so we will translate matching pairs
of get_hd and get_tl back to get_list instructions.
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