Commit Graph

260 Commits

Author SHA1 Message Date
Peter Klausler d6b7576f21 [flang] Fix INQUIRE(PAD=) and (POSITION=) for predefined units
The predefined units were not being initialized with FORM='FORMATTED',
so INQUIRE(PAD=) was failing if no I/O had already been done.

INQUIRE(POSITION=) was returning 'REWIND' on stdin/stdout (which
is somewhat defensible from the definition, and is what Intel Fortran
does), but most implementations return 'ASIS'.  Change the runtime
to return 'REWIND' only for positionable external files, but 'ASIS'
for terminals, sockets, &c.

Differential Revision: https://reviews.llvm.org/D114028
2021-11-17 16:27:35 -08:00
V Donaldson ea8cdf322f [flang] Fix a bug in INQUIRE(IOLENGTH=) output
The inquire by output list form of the INQUIRE statement calculates the
number of file storage units that would be required to store the data
of an output list in an unformatted file.  Currently, the result is
incorrectly multiplied by the number of bytes for a data type.  A query
for "INTEGER(KIND=4) A(10)" should be 40, not 160.

Update formatting.
2021-11-16 11:33:15 -08:00
Jean Perier 2e65c8e8db [flang] Allow write after non advancing read in IO runtime
1. To avoid overwriting the part of the record read in the non advancing read,
the furtherPositionInRecord field must be set to the max of the
furtherPositionInRecord and the positionInRecord at the beginning of the
IO write.

2. To allow any further read to succeed after the write, the unit
beganReadingRecord_ must be set to false when resetting the recordLength
during the write, otherwise, recordLength will not be computed in further
read and an assert is hit (at unit.cpp(398)).

The added unit test exercises both of these scenarios.

Differential Revision: https://reviews.llvm.org/D113740
2021-11-16 14:53:39 +01:00
Peter Klausler da25f968a9 [flang] Runtime performance improvements to real formatted input
Profiling a basic internal real input read benchmark shows some
hot spots in the code used to prepare input for decimal-to-binary
conversion, which is of course where the time should be spent.
The library that implements decimal to/from binary conversions has
been optimized, but not the code in the Fortran runtime that calls it,
and there are some obvious light changes worth making here.

Move some member functions from *.cpp files into the class definitions
of Descriptor and IoStatementState to enable inlining and specialization.

Make GetNextInputBytes() the new basic input API within the
runtime, replacing GetCurrentChar() -- which is rewritten in terms of
GetNextInputBytes -- so that input routines can have the
ability to acquire more than one input character at a time
and amortize overhead.

These changes speed up the time to read 1M random reals
using internal I/O from a character array from 1.29s to 0.54s
on my machine, which on par with Intel Fortran and much faster than
GNU Fortran.

Differential Revision: https://reviews.llvm.org/D113697
2021-11-12 11:40:02 -08:00
Peter Klausler d1b09adeeb [flang] Fix rounding edge case in F output editing
When an Fw.d output edit descriptor has a "d" value exactly
equal to the number of zeroes after the decimal point for a value
(e.g., 0.07 with F5.1), the Fw.d output editing code needs to
do the rounding itself to either 0.0 or 0.1 after performing
a conversion without rounding (to avoid 0.04999 rounding up twice).

Differential Revision: https://reviews.llvm.org/D113698
2021-11-12 11:16:25 -08:00
Peter Klausler 4a0af824ee [flang] Respect NO_STOP_MESSAGE=1 in runtime
When an environment variable NO_STOP_MESSAGE=1 is set,
assume that STOP statements with a successful code
have QUIET=.TRUE.

Differential Revision: https://reviews.llvm.org/D113701
2021-11-12 10:50:36 -08:00
Peter Klausler 85ec449352 [flang] Fix ORDER= argument to RESHAPE
The ORDER= argument to the transformational intrinsic function RESHAPE
was being misinterpreted in an inverted way that could be detected only
with 3-d or higher rank array.  Fix in both folding and the runtime, and
extend tests.

Differential Revision: https://reviews.llvm.org/D113699
2021-11-12 10:25:00 -08:00
Jean Perier 6544d9a4a0 [flang] Fix vector cshift runtime with non zero lower bounds
The source index should not be compared to zero after applying the
shift with the modulo, it must be compared to the lower bound.
Otherwise, the extent is not added in case it should and the computed
source index may be less than the lower bound, causing invalid results.

Differential Revision: https://reviews.llvm.org/D113659
2021-11-12 09:26:08 +01:00
peter klausler 6d44387e21 [flang] Make subscript list argument a nullable pointer
Component::CreatePointerDescriptor unconditionally expects a
vector of subscripts to be passed as an argument, but is called
from NAMELIST input with a null pointer.  Make that argument
a nullable pointer, move it to the end of the argument list,
and give it a default value of nullptr.

Differential Revision: https://reviews.llvm.org/D113312
2021-11-08 11:53:13 -08:00
Peter Klausler e7823608bc [flang] Complete the fix for NAMELIST look-ahead case
When processing the devious NAMELIST input

  &group logarray = t t t
    = 666 /

for LOGICAL::logarray(3) and INTEGER::t, the runtime library
needs to do some look-ahead on the input stream to make sure
that the last "t" on the first line is a truth value rather than
an item name -- which in this case it is.  This look-ahead
was implemented in a previous patch but only worked for internal
input cases; this patch implements look-ahead capabilities for
input from an external file, too (and also adjusts repeated
list-directed input items to use this infrastructure, too).

Differential Revision: https://reviews.llvm.org/D113311
2021-11-08 10:01:16 -08:00
Jean Perier 4375430689 [flang] Set the addendum when establishing pointer section in descriptor
If the source has an addendum, the descriptor that is being established
to describe a section over the source needs to copy the addendum so that
derived type information is correctly set in the descriptor being
established.

This allows namelist IO with derived type to work correctly.

Differential Revision: https://reviews.llvm.org/D113258
2021-11-08 11:05:31 +01:00
Diana Picus 9df0ba599c [flang] Implement GET_ENVIRONMENT_VARIABLE(VALUE)
Implement the second entry point for GET_ENVIRONMENT_VARIABLE. Reuse
existing bits and pieces wherever possible.

This patch also increases CFI_* error codes in order to avoid conflicts.
GET_ENVIRONMENT_VARIABLE is required to return a status of 1 if an
environment variable does not exist and 2 if environment variables are
not supported. However, if we add status codes for that they will
conflict with CFI_ERROR_BASE_ADDR_NULL and CFI_ERROR_BASE_ADDR_NOT_NULL,
which are also 1 and 2 at the moment. We therefore move all CFI error
codes up (an arbitrary) 10 spots to make room. Hopefully this isn't
a problem, since we weren't matching the CFI error codes that gfortran
uses anyway. It may still be an issue if any other runtime functions
will need to return a status of 1 or 2, but we should probably deal with
that when/if it occurs.

Differential Revision: https://reviews.llvm.org/D112698
2021-11-01 09:19:20 +00:00
Peter Klausler 8b5b38eb24 [flang] Revert new unintended runtime behavior
A recent change caused some variable-length sequential formatted
output statements with record positioning at the end of a FORMAT
(e.g., FORMAT('hi',10X) to append blanks at the end of the completed
record when emitting it.

Differential Revision: https://reviews.llvm.org/D112742
2021-10-28 14:11:06 -07:00
Diana Picus 824bf90819 [flang] runtime: Read environment variables directly
Add support for reading environment variables directly, via std::getenv.
This needs to allocate a C-style string to pass into std::getenv. If the
memory allocation for that fails, we terminate.

This also changes the interface for EnvVariableLength to receive the
source file and line so we can crash gracefully.

Note that we are now completely ignoring the envp pointer passed into
ProgramStart, since that could go stale if the environment is modified
during execution.

Differential Revision: https://reviews.llvm.org/D111785
2021-10-28 07:49:30 +00:00
peter klausler b83242e20e [flang] Support legacy usage of 'A' edit descriptors for integer & real
The 'A' edit descriptor once served as a form of raw I/O of bytes
to/from variables that weren't of type CHARACTER (which itself
didn't exist until F'77).  This usage was especially common for
output of numeric variables that had been initialized with Hollerith.

Differential Revision: https://reviews.llvm.org/D112346
2021-10-22 16:02:33 -07:00
peter klausler 89a927c678 [flang] Fix NAMELIST input bug with multiple subscript triplets
NAMELIST input can contain array subscripts with triplet notation.
The calculation of the default effective stride for the constructed
array descriptor was simply incorrect after the first dimension.

Differential Revision: https://reviews.llvm.org/D112347
2021-10-22 15:59:28 -07:00
peter klausler f6aac0dd4d [flang] Fix DOT_PRODUCT for logical
A build-time check in a template class instantiation was applying
a test that's meaningful only for numeric types.

Differential Revision: https://reviews.llvm.org/D112345
2021-10-22 15:56:20 -07:00
peter klausler fbb020fb48 [flang] Extension: allow tabs in output format strings
A CHARACTER variable used as an output format may contain
unquoted tab characters, which are treated as if they had
been quoted.  This is an extension supported by all other
Fortran compilers to which I have access.

Differential Revision: https://reviews.llvm.org/D112350
2021-10-22 15:53:29 -07:00
peter klausler ce71f8e017 [flang] Fix crash on empty formatted external READs
ExternalFileUnit::BeginReadingRecord() must be called at least once
during an external formatted READ statement before FinishReadingRecord().
In the case of a formatted external READ with no data items, the call
to finish processing of the format (which might have lingering control
items that need doing) was taking place before the call to BeginReadingRecord
from ExternalIoStatementState::EndIoStatement.  Add a call to
BeginReadingRecord on this path.

Differential Revision: https://reviews.llvm.org/D112351
2021-10-22 15:48:45 -07:00
Peter Klausler a5a493e192 [flang] Speed common runtime cases of DOT_PRODUCT & MATMUL
Look for contiguous numeric argument arrays at runtime and
use specialized code for them.

Differential Revision: https://reviews.llvm.org/D112239
2021-10-22 14:36:13 -07:00
peter klausler b8452dba28 [flang] Support NAMELIST input of short arrays
NAMELIST array input does not need to fully define an array.
If another input item begins after at least one element,
it ends input into the array and the remaining items are
not modified.

The tricky part of supporting this feature is that it's not
always easy to determine whether the next non-blank thing in
the input is a value or the next item's name, esp. in the case
of logical data where T and F can be names.  E.g.,

  &group logicalArray = t f f t
      = 1 /

should read three elements into "logicalArray" and then read
an integer or real variable named "t".

So the I/O runtime has to do some look-ahead to determine whether
the next thing in the input is a name followed by '=', '(', or '%'.
Since the '=' may be on a later record, possibly with intervening
NAMELIST comments, the runtime has to support a general form of
saving and restoring its current position.  The infrastructure
in the I/O runtime already has to support repositioning for
list-directed repetition, even on non-positionable input sources
like terminals and sockets; this patch adds an internal RAII API
to make it easier to save a position and then do arbitrary
look-ahead.

Differential Revision: https://reviews.llvm.org/D112245
2021-10-22 13:38:11 -07:00
peter klausler b03628d986 [flang] Emit unformatted headers & footers even with RECL=
The runtime library was emitting unformatted record headers and
footers when an external unit had no fixed RECL=.  This is wrong
for sequential files, which should have headers & footers even
with RECL.  Change to omit headers & footers from unformatted
I/O only for direct access files.

Differential Revision: https://reviews.llvm.org/D112243
2021-10-22 11:07:01 -07:00
Diana Picus fc2ba5e53d [flang] Implement GET_ENVIRONMENT_VARIABLE(LENGTH)
Search for the environment variable in the envp string passed to
ProgramStart. This doesn't work if the main program isn't Fortran.

Differential Revision: https://reviews.llvm.org/D111394
2021-10-13 08:42:03 +00:00
peter klausler c5a5517be4 [flang] Fixing Windows build (take 3)
Add explicit casts to replace implicit conversions and
recently deleted assignment operators from uint128.h
used in runtime/edit-output.cpp.
2021-10-12 18:59:33 -07:00
peter klausler f65f830e5f [flang] runtime: fix output B/O/Z editing of "negative" values
B/O/Z integer output editing must not reflect any sign extension
of scalar output values.  Add more size-dependent OutputInteger
I/O APIs and kind instantiations of EditIntegerOutput.

Differential Revision: https://reviews.llvm.org/D111678
2021-10-12 16:02:07 -07:00
peter klausler f05c95f10f [flang] More work on SYSTEM_CLOCK runtime API and implementation
To get proper wrap-around behavior for the various kind parameter
values of the optional COUNT= and COUNT_MAX= dummy arguments to
the intrinsic subroutine SYSTEM_CLOCK, add an extra argument to
the APIs for lowering to pass the integer kind of the actual argument.
Avoid confusion by requiring that both actual arguments have the same
kind when both are present.  The results of the runtime functions
remain std::int64_t and lowering should still convert them before
storing to the actual argument variables.

Rework the implementation a bit to accomodate the dynamic
specification of the kind parameter, and to clean up some coding
issues with preprocessing and templates.

Use the kind of the COUNT=/COUNT_MAX= actual arguments to determine
the clock's resolution, where possible, in conformance with other
Fortran implementations.

Differential Revision: https://reviews.llvm.org/D111281
2021-10-12 09:24:24 -07:00
peter klausler ef44cad53d [flang][NFC] Document behavior for nonspecified/ambiguous cases
Add explicit documentation for a couple of cases where the Fortran
standard has been observed to be ambiguous or nonspecific and we've
had to choose the behavior of the implementation from some possible
alternatives (and may be distinct from other implementations).

Differential Revision: https://reviews.llvm.org/D111446
2021-10-11 11:06:07 -07:00
peter klausler f63dafebf4 [flang] runtime: fix formatted real input regression w/ spaces
Blank input fields must be interpreted as zero, including the case of
virutal space characters generated from record padding at the end of
an input record.  This stopped working sometime in the past few months
for real input (not sure when); here's a fix.

This bug was breaking FCVS test fm111.

Differential Revision: https://reviews.llvm.org/D110765
2021-10-04 16:46:42 -07:00
Jean Perier 7a6ab39e71 [flang] Revert 3 commits pushed by mistake along b7c07ce15f
Revert "[flang][NFC] Add debug dump method to evaluate::Expr and semantics::Symbol"
This reverts commit b0e35fde21.

Revert "[flang] Add a wrapper for Fortran main program"
This reverts commit 2c1ce0755e.

Revert "[flang][NFC] Fix header comments in some runtime headers"
This reverts commit a63f57674d.
2021-10-01 09:01:31 +02:00
Jean Perier 2c1ce0755e [flang] Add a wrapper for Fortran main program
Add a C wrapper that calls the Fortran runtime initialization and
finalization routines as well as the compiled Fortran main program
_QQmain.

Place it in its own library to satisfy shared library builds since it
contains a C main function.

- cc7ac498f9 (diff-fa35a5efa62731fd2845e5e982eca9a2e36439783e11a4e4a463753c2160ec10R53)
- was created in flang/test/Examples/main.c in Eric's branch
2021-10-01 08:45:20 +02:00
peter klausler faa1842875 [flang] Front-end and runtime support for CALL EXIT and ABORT
Support the extension intrinsic subroutines EXIT([status]) and ABORT()
in the intrinsic table and runtime support library.  Lowering remains
to be done.

Differential Revision: https://reviews.llvm.org/D110741
2021-09-30 11:01:22 -07:00
Diana Picus 37089bae29 Reland "[flang] GET_COMMAND_ARGUMENT runtime implementation"
Recommit https://reviews.llvm.org/D109813 and
https://reviews.llvm.org/D109814.

This implements the second and final entry point for GET_COMMAND_ARGUMENT,
handling the VALUE, STATUS and ERRMSG parameters.

It has a small fix in that we're now using memcpy instead of strncpy
(which was a bad idea to begin with, since we're not actually interested
in a string copy).
2021-09-28 12:34:07 +00:00
Diana Picus 6359a4cdbf Revert "[flang] GET_COMMAND_ARGUMENT(VALUE) runtime implementation"
This reverts commit 0446f1299f and
df6302311f.

There's a warning on flang-aarch64-latest-gcc related to strncpy using
the result of strlen as a bound. I'll recommit with a fix.
2021-09-28 12:07:27 +00:00
Diana Picus 0446f1299f [flang] GET_COMMAND_ARGUMENT(ERRMSG) runtime implementation
Implement the final part of GET_COMMAND_ARGUMENT, i.e. the handling of
ERRMSG. This uses some of the infrastructure in stat.h and gets rid of
the magic numbers that we were using for return codes.

Differential Revision: https://reviews.llvm.org/D109814
2021-09-28 08:32:19 +00:00
Diana Picus df6302311f [flang] GET_COMMAND_ARGUMENT(VALUE) runtime implementation
Partial implementation for the second entry point for
GET_COMMAND_ARGUMENT. It handles the VALUE and STATUS arguments, and
doesn't touch ERRMSG.

Differential Revision: https://reviews.llvm.org/D109813
2021-09-28 08:32:19 +00:00
Diana Picus af63d1791b [flang] GET_COMMAND_ARGUMENT(LENGTH) runtime implementation
Implement the ArgumentLength entry point of GET_COMMAND_ARGUMENT. Also
introduce a fixture for the tests.

Note that this also changes the interface for ArgumentLength from
returning a 4-byte integer to returning an 8-byte integer.

Differential Revision: https://reviews.llvm.org/D109227
2021-09-28 08:32:19 +00:00
peter klausler 4393e3776b [flang] Implement READ(SIZE=) and INQUIRE(IOLENGTH=) in runtime
Count input characters corresponding to formatted edit descriptors
for READ(SIZE=); count output bytes for INQUIRE(IOLENGTH=).

The I/O APIs GetSize() and GetLength() were adjusted to return
std::size_t as function results.

Basic unit tests were added (and others fixed).

Differential Revision: https://reviews.llvm.org/D110291
2021-09-23 10:27:56 -07:00
Diana Picus abbb0f901a [flang] Change complex type define in runtime for clang-cl
When compiling the runtime with a version of clang-cl newer than 12, we
define CMPLXF as __builtin_complex, which returns a float _Complex type.
This errors out in contexts where the result of CMPLXF is expected to be
a float_Complex_t. This is defined as _Fcomplex whenever _MSC_VER is
defined (and as float _Complex otherwise).

This patch defines float_Complex_t & friends as _Fcomplex only when
we're using "true" MSVC, and not just clang-pretending-to-be-MSVC. This
should only affect clang-cl >= 12.

Differential Revision: https://reviews.llvm.org/D110139
2021-09-22 06:54:33 +00:00
Jean Perier 05b4e49a17 [flang] Signal EOR in non advancing IO and move to next record
When an end of record is met in non advancing IO:
- Set IOSTAT if present according to 12.11.4 (5).
- Position the file to the next record (12.11.4 (4)).

The previous code was only signaling EOR for fixed record length IO.
Reading at 12.11.4, I do not find the rational for this condition, so I
removed it.
It also does not seem the presence of padding should prevent
the EOR signaling.

The positionning to the next record was block when EOR is signaling
in FinishReadingRecord because ErrorHandler.isError() is true in this
case.
EOR in input is not an error, but I am not confident to modify
ErrorHandler.isError() to cover that. However, In FinishReadingRecord,
the code should not bail if the error is simply an end of record.

I did not check the SIZE requirements here because GetSize runtime is
not yet implemented.

Differential Revision: https://reviews.llvm.org/D109505
2021-09-10 13:08:02 +02:00
Michael Kruse 84e1258feb [flang] Use CMake to determine endianness.
The preprocessor definitions __BYTE_ORDER__, __ORDER_BIG_ENDIAN__, and
__ORDER_LITTLE_ENDIAN__ are gcc extensions (also supported by clang),
but msvc (and others) do not define them. As a result __BYTE_ORDER__
and __ORDER_BIG_ENDIAN__ both evaluate to 0 by the prepreprocessor,
and __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__, the first `#if` condition
to 1, hence assuming the wrong byte order for x86(_64).

This patch instead uses CMake's TestBigEndian module to determine
target architecture's endianness at configure-time.

Note this also uses the same mechanism for the runtime. If compiling
flang as a cross-compiler, the runtime for the compile-target must be
built separately (Flang does not support the LLVM_ENABLE_RUNTIMES
mechanism yet).

Fixes llvm.org/PR51597

Reviewed By: ijan1, Leporacanthicus

Differential Revision: https://reviews.llvm.org/D109108
2021-09-03 15:44:51 -05:00
Peter Klausler 830c0b9023 [flang] Move runtime API headers to flang/include/flang/Runtime
Move the closure of the subset of flang/runtime/*.h header files that
are referenced by source files outside flang/runtime (apart from unit tests)
into a new directory (flang/include/flang/Runtime) so that relative
include paths into ../runtime need not be used.

flang/runtime/pgmath.h.inc is moved to flang/include/flang/Evaluate;
it's not used by the runtime.

Differential Revision: https://reviews.llvm.org/D109107
2021-09-03 11:08:34 -07:00
Diana Picus 0c375296cc [flang] COMMAND_ARGUMENT_COUNT runtime implementation
Grab whatever ProgramStart has stored in executionEnvironment.argc and
subtract 1 (based on the assumption that ProgramStart is called with
a C-style argc that counts the command name as an argument).

Spoiler alert: The tests will evolve into fixtures when we implement
GET_COMMAND_ARGUMENT etc.

Differential Revision: https://reviews.llvm.org/D109048
2021-09-03 07:29:39 +00:00
Diana Picus 651f58bf63 [flang] Remove *- C++ -* incantation from runtime .cpp files. NFC
We should only need to spell the language out in .h files.

Differential Revision: https://reviews.llvm.org/D109138
2021-09-03 07:17:45 +00:00
Jean Perier c5729f2e63 [flang] Set default form if unspecified at end of OPEN statement
The standard specifies that the form must be set to a default at the
end of an open statement (C.7.4 point 2) where it was not specified.
Only in the case of a pre-connected unit can the form be deferred
until the first data transfer statement.

Set back the default form setting in OpenStatementState::EndIoStatement
that had been removed when deferring the pre-connected unit from setting
in 199a623ebf.

Also return "UNDEFINED" instead of "UNKNOWN" to the FORM inquiry when the
form was not yet specified as defined in 12.10.2.12.

Related test: syntax 215a216.

Differential Revision: https://reviews.llvm.org/D108990
2021-09-01 08:40:43 +02:00
Diana Picus 4fae60c4b0 [flang] Add runtime interface for GET_COMMAND_ARGUMENT
GET_COMMAND_ARGUMENT takes a lot of optional arguments: VALUE, LENGTH,
STATUS and ERRMSG. This patch breaks up the interface into 2 different
functions:

* One for getting the LENGTH of an argument.

* One for getting the VALUE and the ERRMSG of an argument. This returns
the STATUS, which can be easily ignored by lowering if it is missing in
the invocation.

Differential Revision: https://reviews.llvm.org/D108688
2021-08-30 07:31:13 +00:00
Diana Picus cc4d28691b [flang] Add runtime interface for COMMAND_ARGUMENT_COUNT
Differential Revision: https://reviews.llvm.org/D108687
2021-08-30 07:31:13 +00:00
Jean Perier b3e392c081 [flang] Implement Posix version of DATE_AND_TIME runtime
Use gettimeofday and localtime_r to implement DATE_AND_TIME intrinsic.
The Windows version fallbacks to the "no date and time information
available" defined by the standard (strings set to blanks and values to
-HUGE).

The implementation uses an ifdef between windows and the rest because
from my tests, the SFINAE approach leads to undeclared name bogus errors
with clang 8 that seems to ignore failure to instantiate is not an error
for the function names (i.e., it understands it should not instantiate
the version using gettimeofday if it is not there, but still yields an
error that it is not declared on the spot where it is called in the
uninstantiated version).

Differential Revision: https://reviews.llvm.org/D108622
2021-08-25 11:16:52 +02:00
peter klausler b232a88c6f [flang] runtime: fix WRITE after BACKSPACE on variable-length file
BACKSPACE leaves "recordLength" set, which is fine for a later READ,
but it causes a later WRITE to fail due to a misinterpretation of the
knowledge of the record length as indication of a fixed-length record
file (RECL=).  Fix.

Differential Revision: https://reviews.llvm.org/D108594
2021-08-24 09:34:52 -07:00
Diana Picus 3330b2532f [flang] Add POSIX implementation for SYSTEM_CLOCK
This is very similar to CPU_TIME, except that we return nanoseconds
rather than seconds. This means we're potentially dealing with rather
large numbers, so we'll have to wrap around to avoid overflows.

Differential Revision: https://reviews.llvm.org/D105970
2021-08-19 07:39:37 +00:00
Diana Picus 0104cc85b1 [flang] Add default implementation for SYSTEM_CLOCK
Add an implementation for the runtime functions related to SYSTEM_CLOCK.
As with CPU_TIME, this is based on std::clock(), which should be
available everywhere, but it is highly recommended to add
platform-specific implementations for systems where std::clock() behaves
poorly (e.g. POSIX).

The documentation for std::clock() doesn't specify a maximum value and
in fact wrap around behaviour is non-conforming.  Therefore, this
implementation of SYSTEM_CLOCK is not guaranteed to wrap around either,
and after std::clock reaches its maximum value we will likely just
return failure rather than wrap around. If this happens often on your
system, please add a new platform-specific implementation.

We define COUNT_MAX as either the maximum value that can be stored in
a std::clock_t or in a 64-bit integer (whichever is smaller), and
COUNT_RATE as CLOCKS_PER_SEC. For POSIX systems, the value of
CLOCKS_PER_SEC is hardcoded to 10^6 and irrelevant for the values
returned by std::clock.

Differential Revision: https://reviews.llvm.org/D105969
2021-08-18 07:39:13 +00:00