We are supporting quadword lock free atomics on AIX. For the situation that users on AIX are using a libatomic that is lock-based for quadword types, we can't enable quadword lock free atomics by default on AIX in case user's new code and existing code accessing the same shared atomic quadword variable, we can't guarentee atomicity. So we need an option to enable quadword lock free atomics on AIX, thus we can build a quadword lock-free libatomic(also for advanced users considering atomic performance critical) for users to make the transition smooth.
Reviewed By: shchenz
Differential Revision: https://reviews.llvm.org/D127189
This patch implements recently ratified extension Zmmul, a subextension
of M (Integer Multiplication and Division) consisting only
multiplication part of it.
Differential Revision: https://reviews.llvm.org/D103313
Reviewed By: craig.topper, jrtc27, asb
[clang] Emit SARIF Diagnostics: Create clang::SarifDocumentWriter interface
Create an interface for writing SARIF documents from within clang:
The primary intent of this change is to introduce the interface
clang::SarifDocumentWriter, which allows incrementally adding
diagnostic data to a JSON backed document. The proposed interface is
not yet connected to the compiler internals, which will be covered in
future work. As such this change will not change the input/output
interface of clang.
This change also introduces the clang::FullSourceRange type that is
modeled after clang::SourceRange + clang::FullSourceLoc, this is useful
for packaging a pair of clang::SourceLocation objects with their
corresponding SourceManagers.
Previous discussions:
RFC for this change: https://lists.llvm.org/pipermail/cfe-dev/2021-March/067907.htmlhttps://lists.llvm.org/pipermail/cfe-dev/2021-July/068480.html
SARIF Standard (2.1.0):
https://docs.oasis-open.org/sarif/sarif/v2.1.0/os/sarif-v2.1.0-os.html
Differential Revision: https://reviews.llvm.org/D109701
When an issue exists in the main file (caller) instead of an included file
(callee), using a `src` pattern applying to the included file may be
inappropriate if it's the caller's responsibility. Add `mainfile` prefix to check
the main filename.
For the example below, the issue may reside in a.c (foo should not be called
with a misaligned pointer or foo should switch to an unaligned load), but with
`src` we can only apply to the innocent callee a.h. With this patch we can use
the more appropriate `mainfile:a.c`.
```
//--- a.h
// internal linkage
static inline int load(int *x) { return *x; }
//--- a.c, -fsanitize=alignment
#include "a.h"
int foo(void *x) { return load(x); }
```
See the updated clang/docs/SanitizerSpecialCaseList.rst for a caveat due
to C++ vague linkage functions.
Reviewed By: #sanitizers, kstoimenov, vitalybuka
Differential Revision: https://reviews.llvm.org/D129832
Follow-up to 6626f6fec3, this fixes the handling of -MT
* If no targets are provided, we need to invent one since cc1 expects
the driver to have handled it. The default is to use -o, quoting as
necessary for a make target.
* Fix the splitting for empty string, which was incorrectly treated as
{""} instead of {}.
* Add a way to test this behaviour in clang-scan-deps.
Differential Revision: https://reviews.llvm.org/D129607
Create an interface for writing SARIF documents from within clang:
The primary intent of this change is to introduce the interface
clang::SarifDocumentWriter, which allows incrementally adding
diagnostic data to a JSON backed document. The proposed interface is
not yet connected to the compiler internals, which will be covered in
future work. As such this change will not change the input/output
interface of clang.
This change also introduces the clang::FullSourceRange type that is
modeled after clang::SourceRange + clang::FullSourceLoc, this is useful
for packaging a pair of clang::SourceLocation objects with their
corresponding SourceManagers.
Previous discussions:
RFC for this change: https://lists.llvm.org/pipermail/cfe-dev/2021-March/067907.htmlhttps://lists.llvm.org/pipermail/cfe-dev/2021-July/068480.html
SARIF Standard (2.1.0):
https://docs.oasis-open.org/sarif/sarif/v2.1.0/os/sarif-v2.1.0-os.html
Differential Revision: https://reviews.llvm.org/D109701
Add support for the RDPRU instruction on Zen2 processors.
User-facing features:
- Clang option -m[no-]rdpru to enable/disable the feature
- Support is implicit for znver2/znver3 processors
- Preprocessor symbol __RDPRU__ to indicate support
- Header rdpruintrin.h to define intrinsics
- "rdpru" mnemonic supported for assembler code
Internal features:
- Clang builtin __builtin_ia32_rdpru
- IR intrinsic @llvm.x86.rdpru
Differential Revision: https://reviews.llvm.org/D128934
This is a recommit of b822efc740,
reverted in dc34d8df4c. The commit caused
fails because the test ast-print-fp-pragmas.c did not specify particular
target, and it failed on targets which do not support constrained
intrinsics. The original commit message is below.
AST does not have special nodes for pragmas. Instead a pragma modifies
some state variables of Sema, which in turn results in modified
attributes of AST nodes. This technique applies to floating point
operations as well. Every AST node that can depend on FP options keeps
current set of them.
This technique works well for options like exception behavior or fast
math options. They represent instructions to the compiler how to modify
code generation for the affected nodes. However treatment of FP control
modes has problems with this technique. Modifying FP control mode
(like rounding direction) usually requires operations on hardware, like
writing to control registers. It must be done prior to the first
operation that depends on the control mode. In particular, such
operations are required for implementation of `pragma STDC FENV_ROUND`,
compiler should set up necessary rounding direction at the beginning of
compound statement where the pragma occurs. As there is no representation
for pragmas in AST, the code generation becomes a complicated task in
this case.
To solve this issue FP options are kept inside CompoundStmt. Unlike to FP
options in expressions, these does not affect any operation on FP values,
but only inform the codegen about the FP options that act in the body of
the statement. As all pragmas that modify FP environment may occurs only
at the start of compound statement or at global level, such solution
works for all relevant pragmas. The options are kept as a difference
from the options in the enclosing compound statement or default options,
it helps codegen to set only changed control modes.
Differential Revision: https://reviews.llvm.org/D123952
This patch gives basic parsing and semantic support for
"parallel masked taskloop simd" construct introduced in
OpenMP 5.1 (section 2.16.10)
Differential Revision: https://reviews.llvm.org/D128946
AST does not have special nodes for pragmas. Instead a pragma modifies
some state variables of Sema, which in turn results in modified
attributes of AST nodes. This technique applies to floating point
operations as well. Every AST node that can depend on FP options keeps
current set of them.
This technique works well for options like exception behavior or fast
math options. They represent instructions to the compiler how to modify
code generation for the affected nodes. However treatment of FP control
modes has problems with this technique. Modifying FP control mode
(like rounding direction) usually requires operations on hardware, like
writing to control registers. It must be done prior to the first
operation that depends on the control mode. In particular, such
operations are required for implementation of `pragma STDC FENV_ROUND`,
compiler should set up necessary rounding direction at the beginning of
compound statement where the pragma occurs. As there is no representation
for pragmas in AST, the code generation becomes a complicated task in
this case.
To solve this issue FP options are kept inside CompoundStmt. Unlike to FP
options in expressions, these does not affect any operation on FP values,
but only inform the codegen about the FP options that act in the body of
the statement. As all pragmas that modify FP environment may occurs only
at the start of compound statement or at global level, such solution
works for all relevant pragmas. The options are kept as a difference
from the options in the enclosing compound statement or default options,
it helps codegen to set only changed control modes.
Differential Revision: https://reviews.llvm.org/D123952
This patch gives basic parsing and semantic support for
"parallel masked taskloop" construct introduced in
OpenMP 5.1 (section 2.16.9)
Differential Revision: https://reviews.llvm.org/D128834
Create an interface for writing SARIF documents from within clang:
The primary intent of this change is to introduce the interface
clang::SarifDocumentWriter, which allows incrementally adding
diagnostic data to a JSON backed document. The proposed interface is
not yet connected to the compiler internals, which will be covered in
future work. As such this change will not change the input/output
interface of clang.
This change also introduces the clang::FullSourceRange type that is
modeled after clang::SourceRange + clang::FullSourceLoc, this is useful
for packaging a pair of clang::SourceLocation objects with their
corresponding SourceManagers.
Previous discussions:
RFC for this change: https://lists.llvm.org/pipermail/cfe-dev/2021-March/067907.htmlhttps://lists.llvm.org/pipermail/cfe-dev/2021-July/068480.html
SARIF Standard (2.1.0):
https://docs.oasis-open.org/sarif/sarif/v2.1.0/os/sarif-v2.1.0-os.html
Differential Revision: https://reviews.llvm.org/D109701
Instead of dumping the string literal (which
quotes it and escape every non-ascii symbol),
we can use the content of the string when it is a
8 byte string.
Wide, UTF-8/UTF-16/32 strings are still completely
escaped, until we clarify how these entities should
behave (cf https://wg21.link/p2361).
`FormatDiagnostic` is modified to escape
non printable characters and invalid UTF-8.
This ensures that unicode characters, spaces and new
lines are properly rendered in static messages.
This make clang more consistent with other implementation
and fixes this tweet
https://twitter.com/jfbastien/status/1298307325443231744 :)
Of note, `PaddingChecker` did print out new lines that were
later removed by the diagnostic printing code.
To be consistent with its tests, the new lines are removed
from the diagnostic.
Unicode tables updated to both use the Unicode definitions
and the Unicode 14.0 data.
U+00AD SOFT HYPHEN is still considered a print character
to match existing practices in terminals, in addition of
being considered a formatting character as per Unicode.
Reviewed By: aaron.ballman, #clang-language-wg
Differential Revision: https://reviews.llvm.org/D108469
This patch gives basic parsing and semantic support for
"masked taskloop simd" construct introduced in OpenMP 5.1 (section 2.16.8)
Differential Revision: https://reviews.llvm.org/D128693
Instead of dumping the string literal (which
quotes it and escape every non-ascii symbol),
we can use the content of the string when it is a
8 byte string.
Wide, UTF-8/UTF-16/32 strings are still completely
escaped, until we clarify how these entities should
behave (cf https://wg21.link/p2361).
`FormatDiagnostic` is modified to escape
non printable characters and invalid UTF-8.
This ensures that unicode characters, spaces and new
lines are properly rendered in static messages.
This make clang more consistent with other implementation
and fixes this tweet
https://twitter.com/jfbastien/status/1298307325443231744 :)
Of note, `PaddingChecker` did print out new lines that were
later removed by the diagnostic printing code.
To be consistent with its tests, the new lines are removed
from the diagnostic.
Unicode tables updated to both use the Unicode definitions
and the Unicode 14.0 data.
U+00AD SOFT HYPHEN is still considered a print character
to match existing practices in terminals, in addition of
being considered a formatting character as per Unicode.
Reviewed By: aaron.ballman, #clang-language-wg
Differential Revision: https://reviews.llvm.org/D108469
This patch gives basic parsing and semantic support for "masked taskloop"
construct introduced in OpenMP 5.1 (section 2.16.7)
Differential Revision: https://reviews.llvm.org/D128478
This patch implements soft reset and adds tests for soft reset success of the
diagnostics engine. This allows us to recover from errors in clang-repl without
resetting the pragma handlers' state.
Differential revision: https://reviews.llvm.org/D126183
Create an interface for writing SARIF documents from within clang:
The primary intent of this change is to introduce the interface
clang::SarifDocumentWriter, which allows incrementally adding
diagnostic data to a JSON backed document. The proposed interface is
not yet connected to the compiler internals, which will be covered in
future work. As such this change will not change the input/output
interface of clang.
This change also introduces the clang::FullSourceRange type that is
modeled after clang::SourceRange + clang::FullSourceLoc, this is useful
for packaging a pair of clang::SourceLocation objects with their
corresponding SourceManagers.
Previous discussions:
RFC for this change: https://lists.llvm.org/pipermail/cfe-dev/2021-March/067907.htmlhttps://lists.llvm.org/pipermail/cfe-dev/2021-July/068480.html
SARIF Standard (2.1.0):
https://docs.oasis-open.org/sarif/sarif/v2.1.0/os/sarif-v2.1.0-os.html
Differential Revision: https://reviews.llvm.org/D109701
HLSL supports half type.
When enable-16bit-types is not set, half will be treated as float.
When enable-16bit-types is set, half will be treated like real 16bit float type and map to llvm half type.
Also change CXXABI to Microsoft to match dxc behavior.
The mangle name for half is "$f16@" when half is treat as native half type and "$halff@" when treat as float.
In AST, half is still half.
The special thing is done at clang codeGen, when NativeHalfType is false, half will translated into float.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D124790
Adding half float to types that can be represented by __attribute__((mode(xx))).
Original implementation authored by George Steed.
Differential Revision: https://reviews.llvm.org/D126479
For amdgpu target long double type is the same as double type.
The width and align of long double type was incorrectly
overridden when copying aux target properties, which
caused assertion in codegen when emitting global
variables with long double type.
This patch fix that by saving and restoring width
and align of long double type.
Reviewed by: Artem Belevich
Differential Revision: https://reviews.llvm.org/D127771
Fixes: SWDEV-335515
Building on D126796, this commit adds the infrastructure for being able
to print out descriptions of what each warning does.
Differential Revision: https://reviews.llvm.org/D126832
While it's not as robust as using the attribute on enums/classes (the
type information may be lost through a function pointer, a declaration
or use of the underlying type without using the typedef, etc) but I
think there's still value in being able to attribute a typedef and have
all return types written with that typedef pick up the
warn_unused_result behavior.
Specifically I'd like to be able to annotate LLVMErrorRef (a wrapper for
llvm::Error used in the C API - the underlying type is a raw pointer, so
it can't be attributed itself) to reduce the chance of unhandled errors.
Differential Revision: https://reviews.llvm.org/D102122
Vector types in hlsl is using clang ext_vector_type.
Declaration of vector types is in builtin header hlsl.h.
hlsl.h will be included by default for hlsl shader.
Reviewed By: Anastasia
Differential Revision: https://reviews.llvm.org/D125052
Vector types in hlsl is using clang ext_vector_type.
Declaration of vector types is in builtin header hlsl.h.
hlsl.h will be included by default for hlsl shader.
Reviewed By: Anastasia
Differential Revision: https://reviews.llvm.org/D125052
This is a support for " #pragma omp atomic compare fail ". It has Parser & AST support for now.
Reviewed By: tianshilei1992
Differential Revision: https://reviews.llvm.org/D123235
The arch or cpu has its default fpu features and versions such as fpuv2_sf/fpuv3_sf.
And there is also -mfpu option to specify and override fpu version and features.
For example, C860 has fpuv3_sf/fpuv3_df feature as default, when
-mfpu=fpv2 is given, fpuv3_sf/fpuv3_df is replaced with fpuv2_sf/fpuv2_df.
Allows emitting define amdgpu_kernel void @func() IR from C or C++.
This replaces the current workflow which is to write a stub in opencl that
calls an external C function implemented in C++ combined through llvm-link.
Calling the resulting function still requires a manual implementation of the
ABI from the host side. The primary application is for more rapid debugging
of the amdgpu backend by permuting a C or C++ test file instead of manually
updating an IR file.
Implementation closely follows D54425. Non-amd reviewers from there.
Reviewed By: yaxunl
Differential Revision: https://reviews.llvm.org/D125970
This patch implements the following floating point negative absolute value
builtins that required for compatibility with the XL compiler:
```
double __fnabs(double);
float __fnabss(float);
```
These builtins will emit :
- fnabs on PWR6 and below, or if VSX is disabled.
- xsnabsdp on PWR7 and above, if VSX is enabled.
Differential Revision: https://reviews.llvm.org/D125506
Emit predefined macros for GPU family. e.g.
for GPU gfx9xx emit __GFX9__, etc.
Reviewed by: Artem Belevich
Differential Revision: https://reviews.llvm.org/D125909
Fix __has_builtin to return 1 only if the requested target features
of a builtin are enabled by refactoring the code for checking
required target features of a builtin and use it in evaluation
of __has_builtin.
Reviewed by: Artem Belevich
Differential Revision: https://reviews.llvm.org/D125829
This makes CLANG_DEFAULT_STD_C(XX) always be defined, defaulting to
lang_unspecified, so you are forced to check its value instead of using
an #ifdef. This should help avoid accidentally omitting the include in
places where that's important, so that the default language version bug
isn't re-introduced.
Reviewed By: hokein, dexonsmith
Differential Revision: https://reviews.llvm.org/D124974
This is necessary in order to pick up the default C/C++ standard from
the CLANG_DEFAULT_STD_C(XX) defines. This fixes a bug that was
introduced when this default language standard code was moved from
Frontend to Basic, making compilers ignore the configured default
language version override.
Fixes a bug introduced by D121375.
Reviewed By: hokein, dexonsmith
Differential Revision: https://reviews.llvm.org/D124974
Currently we define the `__CUDA_ARCH__` macro only in CUDA mode. This
patch allows us to use this macro in OpenMP-offloading mode when
targeting NVPTX.
Reviewed By: tra, tianshilei1992
Differential Revision: https://reviews.llvm.org/D125256
When Clang generates the path prefix (i.e. the path of the directory
where the file is) when generating FILE, __builtin_FILE(), and
std::source_location, Clang uses the platform-specific path separator
character of the build environment where Clang _itself_ is built. This
leads to inconsistencies in Chrome builds where Clang running on
non-Windows environments uses the forward slash (/) path separator
while Clang running on Windows builds uses the backslash (\) path
separator. To fix this, we add a flag -ffile-reproducible (and its
inverse, -fno-file-reproducible) to have Clang use the target's
platform-specific file separator character.
Additionally, the existing flags -fmacro-prefix-map and
-ffile-prefix-map now both imply -ffile-reproducible. This can be
overriden by setting -fno-file-reproducible.
[0]: https://crbug.com/1310767
Differential revision: https://reviews.llvm.org/D122766
Update KEYALL to cover KEYCUDA. Introduce KEYMAX and
a generic way to update KEYALL.
Reviewed by: Dan Liew
Differential Revision: https://reviews.llvm.org/D125396
CUDA/HIP programs use __noinline__ like a keyword e.g.
__noinline__ void foo() {} since __noinline__ is defined
as a macro __attribute__((noinline)) in CUDA/HIP runtime
header files.
However, gcc and clang supports __attribute__((__noinline__))
the same as __attribute__((noinline)). Some C++ libraries
use __attribute__((__noinline__)) in their header files.
When CUDA/HIP programs include such header files,
clang will emit error about invalid attributes.
This patch fixes this issue by supporting __noinline__ as
a keyword, so that CUDA/HIP runtime could remove
the macro definition.
Reviewed by: Aaron Ballman, Artem Belevich
Differential Revision: https://reviews.llvm.org/D124866
C89 allowed a type specifier to be elided with the resulting type being
int, aka implicit int behavior. This feature was subsequently removed
in C99 without a deprecation period, so implementations continued to
support the feature. Now, as with implicit function declarations, is a
good time to reevaluate the need for this support.
This patch allows -Wimplicit-int to issue warnings in C89 mode (off by
default), defaults the warning to an error in C99 through C17, and
disables support for the feature entirely in C2x. It also removes a
warning about missing declaration specifiers that really was just an
implicit int warning in disguise and other minor related cleanups.
This patch turns on support for CR bit accesses for Power8 and above. The reason
why CR bits are turned on as the default for Power8 and above is that because
later architectures make use of builtins and instructions that require CR bit
accesses (such as the use of setbc in the vector string isolate predicate
and bcd builtins on Power10).
This patch also adds the clang portion to allow for turning on CR bits in the
front end if the user so desires to.
Differential Revision: https://reviews.llvm.org/D124060
clang emit wrong code sequence for `int16`(`short`) to `__fp16` conversion,
and that should fix the code gen directly is the right way I think,
but I found there is a FIXME comment in clang/Basic/TargetInfo.h say
that's should be removed in future so I think just let swich to using
generic LLVM IR rather than llvm.convert.to.fp16 intrinsics code gen
path is enough.
```
/// Check whether llvm intrinsics such as llvm.convert.to.fp16 should be used
/// to convert to and from __fp16.
/// FIXME: This function should be removed once all targets stop using the
/// conversion intrinsics.
virtual bool useFP16ConversionIntrinsics() const {
return true;
}
```
Reviewed By: craig.topper
Differential Revision: https://reviews.llvm.org/D124509
clang-tidy's behavior is to add the -W flags, and then map all clang diagnostics
to "clang-diagnostic-foo" pseudo-check-names, then use Checks to filter those.
Previous to this patch, we were handling -W flags but not filtering the
diagnostics, assuming both sets of information encoded the same thing.
However this intersection is nontrivial when diagnostic group hierarchy is
involved. e.g. -Wunused + clang-diagnostic-unused-function should not enable
unused label warnings.
This patch more closely emulates clang-tidy's behavior, while not going to
the extreme of generating tidy check names for all clang diagnostics and
filtering them with regexes.
Differential Revision: https://reviews.llvm.org/D124679
Prevents confusion over which `S` is referenced in the final `else`
branch if such use is added.
Reviewed By: hubert.reinterpretcast
Differential Revision: https://reviews.llvm.org/D124556
Tests that need ASTs have to deal with the awkward control flow of
FrontendAction in some way. There are a few idioms used:
- don't bother with unit tests, use clang -dump-ast
- create an ASTConsumer by hand, which is bulky
- use ASTMatchFinder - works pretty well if matchers are actually
needed, very strange if they are not
- use ASTUnit - this yields nice straight-line code, but ASTUnit is a
terrifically complicated library not designed for this purpose
TestAST provides a very simple way to write straight-line tests: specify
the code/flags and it provides an AST that is kept alive until the
object is destroyed.
It's loosely modeled after TestTU in clangd, which we've successfully
used for a variety of tests.
I've updated a couple of clang tests to use this helper, IMO they're clearer.
Differential Revision: https://reviews.llvm.org/D123668
The recently announced IBM z16 processor implements the architecture
already supported as "arch14" in LLVM. This patch adds support for
"z16" as an alternate architecture name for arch14.
This is extended to all `std::` functions that take a reference to a
value and return a reference (or pointer) to that same value: `move`,
`forward`, `move_if_noexcept`, `as_const`, `addressof`, and the
libstdc++-specific function `__addressof`.
We still require these functions to be declared before they can be used,
but don't instantiate their definitions unless their addresses are
taken. Instead, code generation, constant evaluation, and static
analysis are given direct knowledge of their effect.
This change aims to reduce various costs associated with these functions
-- per-instantiation memory costs, compile time and memory costs due to
creating out-of-line copies and inlining them, code size at -O0, and so
on -- so that they are not substantially more expensive than a cast.
Most of these improvements are very small, but I measured a 3% decrease
in -O0 object file size for a simple C++ source file using the standard
library after this change.
We now automatically infer the `const` and `nothrow` attributes on these
now-builtin functions, in particular meaning that we get a warning for
an unused call to one of these functions.
In C++20 onwards, we disallow taking the addresses of these functions,
per the C++20 "addressable function" rule. In earlier language modes, a
compatibility warning is produced but the address can still be taken.
The same infrastructure is extended to the existing MSVC builtin
`__GetExceptionInfo`, which is now only recognized in namespace `std`
like it always should have been.
This is a re-commit of
fc30901096,
a571f82a50,
64c045e25b, and
de6ddaeef3,
and reverts aa643f455a.
This change also includes a workaround for users using libc++ 3.1 and
earlier (!!), as apparently happens on AIX, where std::move sometimes
returns by value.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D123345
Revert "Fixup D123950 to address revert of D123345"
This reverts commit aa643f455a.
This is extended to all `std::` functions that take a reference to a
value and return a reference (or pointer) to that same value: `move`,
`forward`, `move_if_noexcept`, `as_const`, `addressof`, and the
libstdc++-specific function `__addressof`.
We still require these functions to be declared before they can be used,
but don't instantiate their definitions unless their addresses are
taken. Instead, code generation, constant evaluation, and static
analysis are given direct knowledge of their effect.
This change aims to reduce various costs associated with these functions
-- per-instantiation memory costs, compile time and memory costs due to
creating out-of-line copies and inlining them, code size at -O0, and so
on -- so that they are not substantially more expensive than a cast.
Most of these improvements are very small, but I measured a 3% decrease
in -O0 object file size for a simple C++ source file using the standard
library after this change.
We now automatically infer the `const` and `nothrow` attributes on these
now-builtin functions, in particular meaning that we get a warning for
an unused call to one of these functions.
In C++20 onwards, we disallow taking the addresses of these functions,
per the C++20 "addressable function" rule. In earlier language modes, a
compatibility warning is produced but the address can still be taken.
The same infrastructure is extended to the existing MSVC builtin
`__GetExceptionInfo`, which is now only recognized in namespace `std`
like it always should have been.
This is a re-commit of
fc30901096,
a571f82a50, and
64c045e25b
which were reverted in
e75d8b7037
due to a crasher bug where CodeGen would emit a builtin glvalue as an
rvalue if it constant-folds.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D123345
Kai Luo