Code generation to create and populate the descriptor (element size and
type code) is based on the boxed result type. This does not work well with
unlimited polymorphic entities since the fir type does not represent what is
actually emboxed or reboxed.
In the case of emboxing, the input type will be used to populate
the descriptor element size and type code.
When reboxing an unlimited polymorphic to a unlimited polymorphic entities, the
element size and type code is retrieve from the input box.
Reviewed By: jeanPerier
Differential Revision: https://reviews.llvm.org/D138587
This patch adds the -fpass-plugin option to flang which dynamically loads LLVM
passes from the shared object passed as the argument to the flag. The behavior
of the option is designed to replicate that of the same option in clang and
thus has the same capabilities and limitations.
Features:
Multiple instances of -fpass-plugin=path-to-file can be specified and each
of the files will be loaded in that order.
The flag can be passed to both flang-new and flang-new -fc1.
The flag will be listed when the -help flag is passed to both flang-new and
flang-new -fc1. It will also be listed when the --help-hidden flag is passed.
Limitations:
Dynamically loaded plugins are not supported in clang on Windows and are not
supported in flang either.
Addenda:
Some minor stylistic changes are made in the files that were modified to
enable this functionality. Those changes make the naming of functions more
consistent, but do not change any functionality that is not directly
related to enabling -fpass-plugin.
Differential Revision: https://reviews.llvm.org/D129156
Plugged in propagation of nnan/nsz/arcp/afn/reassoc related options
to lowering/FirOpBuilder.
Reviewed By: jeanPerier, tblah, awarzynski
Differential Revision: https://reviews.llvm.org/D137580
For `-foo=bar`, getSpelling return `-foo=` which is exactly what we need from
the diagnostic. Drop `-` from the err_drv_unsupported_option_argument template.
This change makes `--` long option diagnostics more convenient.
Reviewed By: lenary
Differential Revision: https://reviews.llvm.org/D137659
Added MathOptionsBase to share fastmath config between different
components. Frontend driver translates LangOptions into MathOptionsBase.
FirConverter configures FirOpBuilder using MathOptionsBase
config passed to it via LoweringOptions.
Depends on D137390
Reviewed By: jeanPerier
Differential Revision: https://reviews.llvm.org/D137391
Only add the option processing and store the result. No attributes are
added to FIR yet.
Clang only forwards -mreassociate
if (AssociativeMath && !SignedZeros && !TrappingMath)
Flang doesn't have -f[no-]trapping-math, so this part of the condition
has been omitted. !TrappingMath is the default.
Differential Revision: https://reviews.llvm.org/D137329
Only add the option processing and store the result. No attributes are
added to FIR yet.
This patch follows Clang in forwarding -fno-honor-infinities as
-menable-no-infs.
Reviewed By: kiranchandramohan awarzynski vzakhari
Differential Revision: https://reviews.llvm.org/D137072
Only add the option processing and store the result. No attributes are
added to FIR yet.
Only the "off" and "fast" options are supported. "fast-honor-pragmas" is not applicable because we do not implement `#pragma clang fp contract()` in Fortran [1]. "on" is not supported because it is unclear how to fuse only within individual statements. gfortran also does not implement "on": treating it as an "off".
Currently the default value is "off" to preserve existing behavior. gfortran uses "fast" by default and that may be the right thing for flang-new after further discussion in the future, but that can be changed separately. gfortran's documentation is available [[ https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html | here ]].
[1] https://clang.llvm.org/docs/LanguageExtensions.html#extensions-to-specify-floating-point-flags
Reviewed By: vzakhari, awarzynski
Differential Revision: https://reviews.llvm.org/D136080
In order to be passed as passed-object in the dynamic dispatch, the
polymorphic pointer entity are emboxed. In this process, the dynamic
type must be preserve and pass to fir.embox as the tdesc operand. This
patch introduce a new ExtendedValue that allow to carry over the
dynamic type when the value is unboxed.
Depends on D136820
Reviewed By: PeteSteinfeld
Differential Revision: https://reviews.llvm.org/D136824
Several module files in .../llvm-project/flang/module check for the
existence of the macro "__x86_64__" to conditionally compile Fortran
code. Unfortunately, this macro was not being defined anywhere. This
patch fixes that for compilations targeting 64 bit x86 machines.
I made the following changes --
-- Removed the test for 32 bit X86 targets. The rest of the compiler and
runtime do not support X86 32 bits.
-- Added predefined macros to define "__x86_64__" and "__x86__64" to
be 1 when the target architecture is 64 bit x86 and the "-cpp" option
is on the command line.
-- Changed the cmake file for creating the Fortran module files to use the
"-cpp" option so that the macro "__x86_64__" will be defined when building
the module files.
-- Added a test.
Differential Revision: https://reviews.llvm.org/D135810
To accomplish this, this patch creates an optional list of environment
variable default values to be set by the runtime to allow directly using
the existing runtime implementation of FORT_CONVERT for I/O conversions.
This reverts commit 43fe6f7cc35ded691bbc2fa844086d321e705d46.
Reverting this as CI breaks.
To reproduce, run check-flang, and it will fail with an error saying
.../lib/Bye.so not found in pass-plugin.f90
Add the -fpass-plugin option to flang which dynamically loads LLVM passes from the
shared object passed as the argument to the flag. The behavior of the option is
designed to replicate that of the same option in clang and thus has the same
capabilities and limitations.
- Multiple instances of -fpass-plugin=path-to-file can be specified and each of the
files will be loaded in that order.
- The flag can be passed to both flang-new and flang-new -fc1.
Differential Revision: https://reviews.llvm.org/D129156
The real(10) is supported on x86_64. On aarch64, the value of
selected_real_kind(16) should be 16 rather than 10 since real(10)
is not supported on x86_64. Previously, the real type support check
is not target dependent. Support it now through the target triple
information.
Reviewed By: clementval
Differential Revision: https://reviews.llvm.org/D134021
The real(10) is supported on x86_64. On aarch64, the value of
selected_real_kind(16) should be 16 rather than 10 since real(10)
is not supported on x86_64. Previously, the real type support check
is not target dependent. Support it now through the target triple
information.
Reviewed By: clementval
Differential Revision: https://reviews.llvm.org/D134021
This patch does the following:
- Consumes the PIC flags (fPIC/fPIE/fropi/frwpi etc) in flang-new.
tools::ParsePICArgs() in ToolChains/CommonArgs.cpp is used for this.
- Adds FC1Option to "-mrelocation-model", "-pic-level", and "-pic-is-pie"
command line options.
- Adds the above options to flang/Frontend/CodeGenOptions' data structure.
- Sets the relocation model in the target machine, and
- Sets module flags for the respective PIC/PIE type in LLVM IR.
I have tried my best to replicate how clang does things.
Differential Revision: https://reviews.llvm.org/D131533
Change-Id: I68fe64910be28147dc5617826641cea71b92d94d
This commit addresses concerns raised in D129497.
Propagate lowering options from driver to expressions lowering
via AbstractConverter instance. A single use case so far is
using optimized TRANSPOSE lowering with O1/O2/O3.
bbc does not support optimization level switches, so it uses
default LoweringOptions (e.g. optimized TRANSPOSE lowering
is enabled by default, but an engineering -opt-transpose=false
option can still override this).
Differential Revision: https://reviews.llvm.org/D130204
The options -f{no-}color-diagnostics have been supported in driver. This
supports the behaviors in scanning, parsing, and semantics, and the
behaviors are exactly the same as the driver.
To illustrate the added behaviour, consider the following input file:
```! file.f90
program m
integer :: i = k
end
```
In the following invocations, "error: Must be a constant value" _will be_
formatted:
```
$ flang-new file.f90
error: Semantic errors in file.f90
./file.f90:2:18: error: Must be a constant value
integer :: i = k
```
Note that "error: Semantic errors in file.f90" is also formatted, which
is supported in https://reviews.llvm.org/D126164.
Also note that only "error", "warning" and "portability" are formatted.
Check the following input file:
```! file2.f90
program m
integer :: i =
end
```
```
$ flang-new test2.f90
error: Could not parse test2.f90
./test2.f90:2:11: error: expected '('
integer :: i =
^
./test2.f90:2:3: in the context: statement function definition
integer :: i =
^
...
```
The "error: Could not parse test2.f90" and "error: expected '('" are
formatted. Others such as "in the context" are not formatted yet, which
may or may not be supported.
Reviewed By: awarzynski
Differential Revision: https://reviews.llvm.org/D126166
This update makes sure that `flang-new -O2 -O0` will run at `-O0` rather
than `-O2`.
This bug was identified and originally fixed by Vyacheslav Zakharin in
https://reviews.llvm.org/D130035. I've extracted the fix into a separate
patch.
co-authored by: Vyacheslav Zakharin <vyacheslav.p.zakharin@intel.com>
Differential Revision: https://reviews.llvm.org/D130104
This patch adds support for most common optimisation compiler flags:
`-O{0|1|2|3}`. This is implemented in both the compiler and frontend
drivers. At this point, these options are only used to configure the
LLVM optimisation pipelines (aka middle-end). LLVM backend or MLIR/FIR
optimisations are not supported yet.
Previously, the middle-end pass manager was only required when
generating LLVM bitcode (i.e. for `flang-new -c -emit-llvm <file>` or
`flang-new -fc1 -emit-llvm-bc <file>`). With this change, it becomes
required for all frontend actions that are represented as
`CodeGenAction` and `CodeGenAction::executeAction` is refactored
accordingly (in the spirit of better code re-use).
Additionally, the `-fdebug-pass-manager` option is enabled to facilitate
testing. This flag can be used to configure the pass manager to print
the middle-end passes that are being run. Similar option exists in Clang
and the semantics in Flang are identical. This option translates to
extra configuration when setting up the pass manager. This is
implemented in `CodeGenAction::runOptimizationPipeline`.
This patch also adds some bolier plate code to manage code-gen options
("code-gen" refers to generating machine code in LLVM in this context).
This was extracted from Clang. In Clang, it simplifies defining code-gen
options and enables option marshalling. In Flang, option marshalling is
not yet supported (we might do at some point), but being able to
auto-generate some code with macros is beneficial. This will become
particularly apparent when we start adding more options (at least in
Clang, the list of code-gen options is rather long).
Differential Revision: https://reviews.llvm.org/D128043
This patch refines //when// driver diagnostics are formatted so that
`flang-new` and `flang-new -fc1` behave consistently with `clang` and
`clang -cc1`, respectively. This change only applies to driver diagnostics.
Scanning, parsing and semantic diagnostics are separate and not covered here.
**NEW BEHAVIOUR**
To illustrate the new behaviour, consider the following input file:
```! file.f90
program m
integer :: i = k
end
```
In the following invocations, "error: Semantic errors in file.f90" _will be_
formatted:
```
$ flang-new file.f90
error: Semantic errors in file.f90
./file.f90:2:18: error: Must be a constant value
integer :: i = k
$ flang-new -fc1 -fcolor-diagnostics file.f90
error: Semantic errors in file.f90
./file.f90:2:18: error: Must be a constant value
integer :: i = k
```
However, in the following invocations, "error: Semantic errors in file.f90"
_will not be_ formatted:
```
$ flang-new -fno-color-diagnostics file.f90
error: Semantic errors in file.f90
./file.f90:2:18: error: Must be a constant value
integer :: i = k
$ flang-new -fc1 file.f90
error: Semantic errors in file.f90
./file.f90:2:18: error: Must be a constant value
integer :: i = k
```
Before this change, none of the above would be formatted. Note also that the
default behaviour in `flang-new` is different to `flang-new -fc1` (this is
consistent with Clang).
**NOTES ON IMPLEMENTATION**
Note that the diagnostic options are parsed in `createAndPopulateDiagOpt`s in
driver.cpp. That's where the driver's `DiagnosticEngine` options are set. Like
most command-line compiler driver options, these flags are "claimed" in
Flang.cpp (i.e. when creating a frontend driver invocation) by calling
`getLastArg` rather than in driver.cpp.
In Clang's Options.td, `defm color_diagnostics` is replaced with two separate
definitions: `def fcolor_diagnostics` and def fno_color_diagnostics`. That's
because originally `color_diagnostics` derived from `OptInCC1FFlag`, which is a
multiclass for opt-in options in CC1. In order to preserve the current
behaviour in `clang -cc1` (i.e. to keep `-fno-color-diagnostics` unavailable in
`clang -cc1`) and to implement similar behaviour in `flang-new -fc1`, we can't
re-use `OptInCC1FFlag`.
Formatting is only available in consoles that support it and will normally mean that
the message is printed in bold + color.
Co-authored-by: Andrzej Warzynski <andrzej.warzynski@arm.com>
Reviewed By: rovka
Differential Revision: https://reviews.llvm.org/D126164
This relatively small change will allow Flang's frontend driver,
`flang-new -fc1`, to consume and parse MLIR files. Semantically (i.e.
from user's perspective) this is identical to reading LLVM IR files.
Two file extensions are associated with MLIR files: .fir and .mlir. Note
that reading MLIR files makes only sense when running one of the
code-generation actions, i.e. when using one of the following action
flags: -S, -emit-obj, -emit-llvm, -emit-llvm-bc.
The majority of tests that required `tco` to run are updated to also run
with `flang-new -fc1`. A few tests are updated to use `fir-opt` instead
of `tco` (that's the preferred choice when testing a particular MLIR
pass). basic-program.fir is not updated as that test is intended to
verify the behaviour of `tco` specifically.
Differential Revision: https://reviews.llvm.org/D126890
Until now, `-x` wasn't really taken into account in Flang's compiler and
frontend drivers. `flang-new` and `flang-new -fc1` only recently gained
powers to consume inputs other than Fortran files and that's probably
why this hasn't been noticed yet.
This patch makes sure that `-x` is supported correctly and consistently
with Clang. To this end, verification is added when reading LLVM IR
files (i.e. IR modules are verified with `llvm::verifyModule`). This
way, LLVM IR parsing errors are correctly reported to Flang users. This
also aids testing.
With the new functionality, we can verify that `-x ir` breaks
compilation for e.g. Fortran files and vice-versa. Tests are updated
accordingly.
Differential Revision: https://reviews.llvm.org/D127207
This patch re-factors the driver code in LLVM Flang (frontend +
compiler) to use the MLIR style. For more context, please see:
https://discourse.llvm.org/t/rfc-coding-style-in-the-driver/
Most changes here are rather self-explanatory. Accessors are renamed to
be more consistent with the rest of LLVM (e.g. allSource -->
getAllSources). Additionally, MLIR clang-tidy files are added in the
affected directories.
clang-tidy and clang-format files were copied from MLIR. Small
additional changes are made to silence clang-tidy/clang-format
warnings.
[1] https://mlir.llvm.org/getting_started/DeveloperGuide/
Differential Revision: https://reviews.llvm.org/D125007
*SUMMARY*
Currently, the frontend driver assumes that a target triple is either:
* provided by the frontend itself (e.g. when lowering and generating
code),
* specified through the `-triple/-target` command line flags.
If `-triple/-target` is not used, the frontend will simply use the host
triple.
This is going to be insufficient when e.g. consuming an LLVM IR file
that has no triple specified (reading LLVM files is WIP, see D124667).
We shouldn't require the triple to be specified via the command line in
such situation. Instead, the frontend driver should contain a good
default, e.g. the host triple.
This patch updates Flang's `CompilerInvocation` to do just that, i.e.
defines its default target triple. Similarly to Clang:
* the default `CompilerInvocation` triple is set as the host triple,
* the value specified with `-triple` takes precedence over the frontend
driver default and the current module triple,
* the frontend driver default takes precedence over the module triple.
*TESTS*
This change requires 2 unit tests to be updated. That's because relevant
frontend actions are updated to assume that there's always a valid
triple available in the current `CompilerInvocation`. This update is
required because the unit tests bypass the regular `CompilerInvocation`
set-up (in particular, they don't call
`CompilerInvocation::CreateFromArgs`). I've also taken the liberty to
disable the pre-precossor formatting in the affected unit tests as well
(it is not required).
No new tests are added. As `flang-new -fc1` does not support consuming
LLVM IR files just yet, it is not possible to compile an LLVM IR file
without a triple. More specifically, atm all LLVM IR files are generated
and stored internally and the driver makes sure that these contain a
valid target triple. This is about to change in D124667 (which adds
support for reading LLVM IR/BC files) and that's where tests for
exercising the default frontend driver triple will be added.
*WHAT DOES CLANG DO?*
For reference, the default target triple for Clang's
`CompilerInvocation` is set through option marshalling infra [1] in
Options.td. Please check the definition of the `-triple` flag:
```
def triple : Separate<["-"], "triple">,
HelpText<"Specify target triple (e.g. i686-apple-darwin9)">,
MarshallingInfoString<TargetOpts<"Triple">, "llvm::Triple::normalize(llvm::sys::getDefaultTargetTriple())">,
AlwaysEmit, Normalizer<"normalizeTriple">;
```
Ideally, we should re-use the marshalling infra in Flang.
[1] https://clang.llvm.org/docs/InternalsManual.html#option-marshalling-infrastructure
Differential Revision: https://reviews.llvm.org/D124664
This patch basically implements [1] in ExecuteCompilerInvocation.cpp. It
also:
* replaces `CreateFrontendBaseAction` with `CreateFrontendAction`
(only one method is needed ATM, this change removes the extra
indirection)
* removes `InvalidAction` from the `ActionKind` enum (I don't think it
adds much and keeping it would mean adding a new void case in
`CreateFrontendAction`)
* sets the default frontend action in FrontendOptions.h to
`ParseSyntaxOnly` (note that this is still overridden independently
in `ParseFrontendArg` in CompilerInvocation.cpp)
No new functionality is added, hence no tests.
[1] https://llvm.org/docs/CodingStandards.html#don-t-use-default-labels-in-fully-covered-switches-over-enumerations
Differential Revision: https://reviews.llvm.org/D124245
The semantics of `-mmlir` are identical to `-mllvm`. The only notable
difference is that `-mmlir` options should be forwarded to MLIR rather
than LLVM.
Note that MLIR llvm::cl options are lazily constructed on demand (see
the definition of options in PassManagerOptions.cpp). This means that:
* MLIR global options are only visible when explicitly initialised and
displayed only when using `-mmlir --help`,
* Flang and LLVM global options are always visible and displayed when
using either `-mllvm -help` or `-mmlir --help`.
In other words, `-mmlir --help` is a superset of `-mllvm --help`. This is not
ideal, but we'd need to refactor all option definitions in Flang and
LLVM to improve this. I suggesting leaving this for later.
Differential Revision: https://reviews.llvm.org/D123297
Support for generating LLVM BC files is added in Flang's compiler and
frontend drivers. This requires the `BitcodeWriterPass` pass to be run
on the input LLVM IR module and is implemented as a dedicated frontend
aciton. The new functionality as seen by the user (compiler driver):
```
flang-new -c -emit-llvm file.90
```
or (frontend driver):
```
flang-new -fc1 -emit-llvm-bc file.f90
```
The new behaviour is consistent with `clang` and `clang -cc1`.
Differential Revision: https://reviews.llvm.org/D123211
Any header or module file in the Flang source directory is of no use to
the compiler unless it is copied into the build directory. Indeed, all
compiler search paths are relative to the compiler executable (flang-new
in our case). Hence, "omp_lib.h" should be copied into the build
directory alongside other compiler-provided files that can be "included"
(header files) or "used" (module files).
For now, "omp_lib.h" is copied into "<build-dir>/include/flang/OpenMP".
We may decide to change this in future. For example, Clang copies a
bunch of runtime headers into “<build-dir>/lib/clang/<version-number>”.
We could also consider using a similar header from a different
sub-project.
Flang's driver search path is updated accordingly. A rule for
"installing" the "omp_lib.h" header is _yet to be added_ (we will also
need to determine the suitable location for this).
Differential Revision: https://reviews.llvm.org/D122015
This option is added in both `flang-new` (the compiler driver) and
`flang-new -fc1` (the frontend driver). The semantics are consistent
with `clang` and `clang -cc1`.
As Flang does not run any LLVM passes when invoked with `-emit-llvm`
(i.e. `flang-new -S -emit-llvm <file>`), the tests use
`-S`/`-c`/`-emit-obj` instead. These options require an LLVM backend to
be run by the driver to generate the output (this makese `-mllvm`
relevant here).
Differential Revision: https://reviews.llvm.org/D121374
This patch adds support for:
* `-S` in Flang's compiler and frontend drivers,
and implements:
* `-emit-obj` in Flang's frontend driver and `-c` in Flang's compiler
driver (this is consistent with Clang).
(these options were already available before, but only as placeholders).
The semantics of these options in Clang and Flang are identical.
The `EmitObjAction` frontend action is renamed as `BackendAction`. This
new name more accurately reflects the fact that this action will
primarily run the code-gen/backend pipeline in LLVM. It also makes more
sense as an action implementing both `-emit-obj` and `-S` (originally,
it was just `-emit-obj`).
`tripleName` from FirContext.cpp is deleted and, when a target triple is
required, `mlir::LLVM::LLVMDialect::getTargetTripleAttrName()` is used
instead. In practice, this means that `fir.triple` is replaced with
`llvm.target_triple`. The former was effectively ignored. The latter is
used when lowering from the LLVM dialect in MLIR to LLVM IR (i.e. it's
embedded in the generated LLVM IR module). The driver can then re-use
it when configuring the backend. With this change, the LLVM IR files
generated by e.g. `tco` will from now on contain the correct target
triple.
The code-gen.f90 test is replaced with code-gen-x86.f90 and
code-gen-aarch64.f90. With 2 seperate files we can verify that
`--target` is correctly taken into account. LIT configuration is updated
to enable e.g.:
```
! REQUIRES: aarch64-registered-target
```
Differential Revision: https://reviews.llvm.org/D120568
This patch adds support for dumping the pre-FIR tree in `flang-new
-fc1`, i.e. Flang's frontend driver. This flag is functionally identical
to `-pft-test` in `bbc` and semantically similar to
`-fdebug-dump-parse-tree` from `flang-new -fc1`.
Differential Revision: https://reviews.llvm.org/D121198
This patch adds support for:
* `--target` in the compiler driver (`flang-new`)
* `--triple` in the frontend driver (`flang-new -fc1`)
The semantics of these flags are inherited from `clangDriver`, i.e.
consistent with `clang --target` and `clang -cc1 --triple`,
respectively.
A new structure is defined, `TargetOptions`, that will hold various
Frontend options related to the target. Currently, this is mostly a
placeholder that contains the target triple. In the future, it will be
used for storing e.g. the CPU to tune for or the target features to
enable.
Additionally, the following target/triple related options are enabled
[*]: `-print-effective-triple`, `-print-target-triple`. Definitions in
Options.td are updated accordingly and, to facilated testing,
`-emit-llvm` is added to the list of options available in `flang-new`
(previously it was only enabled in `flang-new -fc1`).
[*] These options were actually available before (like all other options
defined in `clangDriver`), but not included in `flang-new --help`.
Before this change, `flang-new` would just use `native` for defining the
target, so these options were of little value.
Differential Revision: https://reviews.llvm.org/D120246
This patch adds support for the `-emit-llvm` option in the frontend
driver (i.e. `flang-new -fc1`). Similarly to Clang, `flang-new -fc1
-emit-llvm file.f` will generate a textual LLVM IR file.
Depends on D118985
Differential Revision: https://reviews.llvm.org/D119012
This patch adds support for generating MLIR files in Flang's frontend
driver (i.e. `flang-new -fc1`). `-emit-fir` is added as an alias for
`-emit-mlir`. We may want to decide to split the two in the future.
A new parent class for code-gen frontend actions is introduced:
`CodeGenAction`. We will be using this class to encapsulate logic shared
between all code-generation actions, but not required otherwise. For
now, it will:
* run prescanning, parsing and semantic checks,
* lower the input to MLIR.
`EmitObjAction` is updated to inherit from this class. This means that
the behaviour of `flang-new -fc1 -emit-obj` is also updated (previously,
it would just exit immediately). This change required
`flang/test/Driver/syntax-only.f90` to be updated.
For `-emit-fir`, a specialisation of `CodeGenAction` is introduced:
`EmitMLIRAction`. The key logic for this class is implemented in
`EmitMLIRAction::ExecuteAction`.
Differential Revision: https://reviews.llvm.org/D118985
For "USE, INTRINSIC", search only for intrinsic modules;
for "USE, NON_INTRINSIC", do not recognize intrinsic modules.
Allow modules of both kinds with the same name to be used in
the same source file (but not in the same scoping unit, a
constraint of the standard that is now enforced).
The symbol table's scope tree now has a single instance of
a scope with a new kind, IntrinsicModules, whose children are
the USE'd intrinsic modules (explicit or not). This separate
"top-level" scope is a child of the single global scope and
it allows both intrinsic and non-intrinsic modules of the same
name to exist in the symbol table. Intrinsic modules' scopes'
symbols now have the INTRINSIC attribute set.
The search path directories need to make a distinction between
regular directories and the one(s) that point(s) to intrinsic
modules. I allow for multiple intrinsic module directories in
the second search path, although only one is needed today.
Differential Revision: https://reviews.llvm.org/D118631
