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Literal tags are used by the VM as an alternative to reserving a large
virtual memory space in order to be able to quickly identify which terms
are literals. The use of literal tags harms performance, but is useful
to support systems where allocating a large amount of virtual memory is
not an option.
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HiPE has had metadata for gc safety on it's temporaries for a while, but
it has never been enforced or even checked, so naturally several
gc-safety violations has slipped through.
A new pass, hipe_rtl_verify_gcsafe verifies gcsafety on optimised RTL
and is used when running the testsuite, and can be manually enabled with
+{hipe,[verify_gcsafe]}.
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branch and alub overlap in their use cases, but the backends rely on
knowing that the result is unused in their lowering of branch. By
extending alub so that the destination is optional, it can fully replace
branch.
This simplifies rtl by reducing code duplication and the number of
instructions.
Also, in the x86 and arm backends, we can now use 'test' and
{'tst','mvn','teq'} to lower some alubs without destinations. This is
particularly good for x86, as sequences such as 'is_boxed' type tests
now get shorter (both from not needing a mov to copy the variable, but
also from the fact that 'testb' encodes shorter than 'andq').
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This fixes a HiPE bug reported on erlang-questions on 2/11/2016.
The BEAM to ICode tranaslation of the bs_match_string instruction,
written long ago for binaries (i.e., with byte-sized strings), tried
to do a `clever' translation of even bit-sized strings using a HiPE
primop that took a `Size' argument expressed in *bytes*.
ICode is not really the place to do such a thing, and moreover there
is really no reason for the HiPE primop not to take a Size argument
expressed in *bits* instead. This commit changes the `Size' argument
to be in bits, postpones the translation of the bs_match_string primop
Fixed in a pair-programming/debugging session with @margnus1.
until RTL and does a proper translation using bit-sized quantities there.
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* margnus1/bs_unit_fix:
hipe: Fix signed compares of unsigned sizes
beam: Fix overflow bug in i_bs_add_jId
hipe: Add tests for bad bit syntax float sizes
Add a case testing the handling of guards involving binaries
Add some more binary syntax construction tests
hipe: Guard against enormous numbers in ranges
hipe: Fix constructing huge binaries
hipe: Fix binary constructions failing with badarith
Add missing corner-case to bs_construct_SUITE
hipe: Allow unsigned args in hipe_rtl_arith
hipe: test unit size match in bs_put_binary_all
hipe: test unit size match in bs_append
Fix hipe_rtl_binary_construct:floorlog2/1
OTP-13272
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The code generated by the HiPE compiler for pattern matching with
UTF binaries was such that sometimes THE_NON_VALUE was stored in
the roots followed by the garbage collector. This was not an issue
for the vanilla native code compiler, but was problematic for the
ErLLVM back-end.
Fix the issue by not storing THE_NON_VALUE in the live roots. An
alternative fix would be to change the code of the garbage collector.
With this fix, there are no more (known) failing test cases for the
ErLLVM back-end (at least on x86_64 with LLVM 3.5, which is the
configuation regularly tested). Thanks to @margnus1 for the fix.
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Also, some of the branches were testing sizes in bits against a constant
?MAX_BINSIZE, which was in bytes. The signed comparisons masked this
mistake. These branches have been removed since all sizes in bits that
fit in a machine word are valid binary sizes.
Finally, a test that reproduces the issue was added to bs_construct,
along with a test for one of the cases (bs_init<0>(...)) when the test
against ?MAX_BINSIZE must be changed to unsigned rather than removed.
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Bugs were fixed in
hipe_rtl_binary_match:{first_part/3,make_size/3,set_high/1} in commit
5aea81c49, but it turns out these had been copy-pasted verbatim into
hipe_rtl_binary_construct, where they were causing further bugs. They
have now moved to hipe_rtl_binary, from where they are included by the
other two modules.
Furthermore, first_part/3 (reamed get_word_integer/3, since it loads
integers that fits into an unsigned word), and make_size/3 now accepts a
fourth argument to distinguish too large arguments (which should cause a
system_limit exception) from negative or non-integral arguments.
The use of first_part/3 (get_word_integer/3) from 5aea81c49 in
hipe_rtl_binary_construct now allows several binary construction
instructions to accept bignum sizes, as they were supposed to.
Additionally, calls to
hipe_rtl_binary_construct:check_and_untag_fixnum/3 were replaced with
get_word_integer/4 since all of them were also supposed to accept
sufficiently small bignums, but didn't, and check_and_untag_fixnum/3 was
essentially identical to first_part/3 anyway.
HiPE is now capable of passing bs_construct_SUITE completely unmodified.
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In certain cases of matching with very big binaries, the HiPE compiler
generated code that would fail the match, even in cases that the matching
was successful. The problem was more quite noticeable on 32-bit platforms
where certain integer quantities would be represented as bignums.
Brief summary of changes:
* gen_rtl({bs_skip_bits, ...}, ...) could not handle too large constants.
Previously the constants were truncated to word size.
* hipe_rtl_binary_match:make_size/3 erroneously assumed that the output
of first_part/3 would not overflow when multiplied by 8, which is no
longer true. To maintain full performance, the overflow test is only
performed when BitsVar was a bignum. Thus, the fast path is identical
to before.
* hipe_rtl_binary_match:set_high/2 was assuming that only bits below
bit 27 were ever set in arguments to bs_skip_bits, which is not only
false when the arguments are bignums, but also on 64-bit platforms.
The commit includes a test taken from the bs_match_bin_SUITE.
Most of the credit for finding these HiPE compiler errors and for
creating appropriate fixes for them should go to Magnus Lång.
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Only call emasculate_binary if ProcBin.flags is set,
which means it's a writable binary.
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Seen symptom: Hipe compiled code with <<C/utf8, ...>> = Bin does sometimes
not match even though Bin contains a valid utf8 character. There might be
other possible binary matching symptoms, as the problem is not utf8
specific.
Problem: A writable binary was not "emasculated" when the matching started
(as it should) by the hipe compiled code.
Fix: Add a new primop emasculate_binary(Bin) that is called when
a matchstate is created.
ToDo: There are probably room for optimization. For example only call
emasculate_binary if ProcBin.flags is set.
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Prior to R16B, the bs_match_string instruction worked only for cases
that had a destination variable. As shown by the example below, this
is not always the case and the Dst list can be empty.
test(<<42, _/bits>> = B) -> B.
This fixes a bug reported by Loïc Hoguin (02/12/2013); the original
post used a different code example to illustrate the problem.
While revising the code, a significant clean up was also performed.
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