Check applied to unbounded (incomplete) arrays and pointers to spot
cases where the computed address is beyond the largest possible
addressable extent of the array, based on the address space in which the
array is delcared, or which the pointer refers to.
Check helps to avoid cases of nonsense pointer math and array indexing
which could lead to linker failures or runtime exceptions. Of
particular interest when building for embedded systems with small
address spaces.
This is version 2 of this patch -- version 1 had some testing issues
due to a sign error in existing code. That error is corrected and
lit test for this chagne is extended to verify the fix.
Originally reviewed/accepted by: aaron.ballman
Original revision: https://reviews.llvm.org/D86796
Reviewed By: aaron.ballman, ebevhan
Differential Revision: https://reviews.llvm.org/D88174
Check applied to unbounded (incomplete) arrays and pointers to spot
cases where the computed address is beyond the largest possible
addressable extent of the array, based on the address space in which the
array is delcared, or which the pointer refers to.
Check helps to avoid cases of nonsense pointer math and array indexing
which could lead to linker failures or runtime exceptions. Of
particular interest when building for embedded systems with small
address spaces.
This is version 2 of this patch -- version 1 had some testing issues
due to a sign error in existing code. That error is corrected and
lit test for this chagne is extended to verify the fix.
Originally reviewed/accepted by: aaron.ballman
Original revision: https://reviews.llvm.org/D86796
Reviewed By: aaron.ballman, ebevhan
Differential Revision: https://reviews.llvm.org/D88174
This patch solves an error such as:
incompatible operand types ('vbool4_t' (aka '__rvv_bool4_t') and '__rvv_bool4_t')
when one of the value is a TypedefType of the other value in ?:.
Reviewed By: rjmccall
Differential Revision: https://reviews.llvm.org/D103603
This patch adds supports for inline assembly operands and some simple
operand constraints, including register and constant operands.
Differential Revision: https://reviews.llvm.org/D102585
Add front end diagnostics to report error for unimplemented TLS models set by
- compiler option `-ftls-model`
- attributes like `__thread int __attribute__((tls_model("local-exec"))) var_name;`
Reviewed by: aaron.ballman, nemanjai, PowerPC
Differential Revision: https://reviews.llvm.org/D102070
Summary:
Test and produce warning for subtracting a pointer from null or subtracting
null from a pointer. Reuse existing warning that this is undefined
behaviour. Also add unit test for both warnings.
Reformat to satisfy clang-format.
Respond to review comments: add additional test.
Respond to review comments: Do not issue warning for nullptr - nullptr
in C++.
Fix indenting to satisfy clang-format.
Respond to review comments: Add C++ tests.
Author: Jamie Schmeiser <schmeise@ca.ibm.com>
Reviewed By: efriedma (Eli Friedman), nickdesaulniers (Nick Desaulniers)
Differential Revision: https://reviews.llvm.org/D98798
Warn when a declaration uses an identifier that doesn't obey the reserved
identifier rule from C and/or C++.
Differential Revision: https://reviews.llvm.org/D93095
These are intended to mimic warnings available in gcc.
-Wunused-but-set-variable is triggered in the case of a variable which
appears on the LHS of an assignment but not otherwise used.
For instance:
void f() {
int x;
x = 0;
}
-Wunused-but-set-parameter works similarly, but for function parameters
instead of variables.
In C++, they are triggered only for scalar types; otherwise, they are
triggered for all types. This is gcc's behavior.
-Wunused-but-set-parameter is controlled by -Wextra, while
-Wunused-but-set-variable is controlled by -Wunused. This is slightly
different from gcc's behavior, but seems most consistent with clang's
behavior for -Wunused-parameter and -Wunused-variable.
Reviewed By: aeubanks
Differential Revision: https://reviews.llvm.org/D100581
When an object is allocated in a non-default address space we do not
need to check for a constructor if it is not initialized and has a
trivial constructor (which we won't call then).
Reviewed By: JonChesterfield
Differential Revision: https://reviews.llvm.org/D100929
This is a Clang-only change and depends on the existing "musttail"
support already implemented in LLVM.
The [[clang::musttail]] attribute goes on a return statement, not
a function definition. There are several constraints that the user
must follow when using [[clang::musttail]], and these constraints
are verified by Sema.
Tail calls are supported on regular function calls, calls through a
function pointer, member function calls, and even pointer to member.
Future work would be to throw a warning if a users tries to pass
a pointer or reference to a local variable through a musttail call.
Reviewed By: rsmith
Differential Revision: https://reviews.llvm.org/D99517
Similar to variables with an initializer, this is never valid in
standard C, so we can safely constant-fold as an extension. I ran into
this construct in a couple proprietary codebases.
While I'm here, drive-by fix for 090dd647: we should only fold variables
with VLA types, not arbitrary variably modified types.
Differential Revision: https://reviews.llvm.org/D98363
This change splits '-Wtautological-unsigned-zero-compare' by reporting
char-expressions-interpreted-as-unsigned under a separate diagnostic
'-Wtautological-unsigned-char-zero-compare'. This is beneficial for
projects that want to enable '-Wtautological-unsigned-zero-compare' but at
the same time want to keep code portable for platforms with char being
signed or unsigned, such as Chromium.
Differential Revision: https://reviews.llvm.org/D99808
These proposals make the same changes to both C++ and C and remove a
restriction on standard attributes appearing multiple times in the same
attribute list.
We could warn on the duplicate attributes, but do not. This is for
consistency as we do not warn on attributes duplicated within the
attribute specifier sequence. If we want to warn on duplicated
standard attributes, we should do so both for both situations:
[[foo, foo]] and [[foo]][[foo]].
Clang currently has a bug where it allows you to write [[foo bar]] and
both attributes are silently accepted. This patch corrects the comma
parsing rules for such attributes and handles the test case fallout, as
a few tests were accidentally doing this.
This implements C-style type conversions for matrix types, as specified
in clang/docs/MatrixTypes.rst.
Fixes PR47141.
Reviewed By: fhahn
Differential Revision: https://reviews.llvm.org/D99037
I have been trying to statically find and analyze all calls to heap
allocation functions to determine how many of them use sizes known at
compile time vs only at runtime. While doing so I saw that quite a few
projects use replaceable function pointers for heap allocation and noticed
that clang was not able to annotate functions pointers with alloc_size.
I have changed the Sema checks to allow alloc_size on all function pointers
and typedefs for function pointers now and added checks that these
attributes are propagated to the LLVM IR correctly.
With this patch we can also compute __builtin_object_size() for calls to
allocation function pointers with the alloc_size attribute.
Reviewed By: aaron.ballman, erik.pilkington
Differential Revision: https://reviews.llvm.org/D55212
Recently atomicrmw started to support fadd/fsub:
https://reviews.llvm.org/D53965
However clang atomic builtins fetch add/sub still does not support
emitting atomicrmw fadd/fsub.
This patch adds that.
Reviewed by: John McCall, Artem Belevich, Matt Arsenault, JF Bastien,
James Y Knight, Louis Dionne, Olivier Giroux
Differential Revision: https://reviews.llvm.org/D71726
Currently, when one or more attributes are mutually exclusive, the
developer adding the attribute has to manually emit diagnostics. In
practice, this is highly error prone, especially for declaration
attributes, because such checking is not trivial. Redeclarations
require you to write a "merge" function to diagnose mutually exclusive
attributes and most attributes get this wrong.
This patch introduces a table-generated way to specify that a group of
two or more attributes are mutually exclusive:
def : MutualExclusions<[Attr1, Attr2, Attr3]>;
This works for both statement and declaration attributes (but not type
attributes) and the checking is done either from the common attribute
diagnostic checking code or from within mergeDeclAttribute() when
merging redeclarations.
```
Warn when a function pointer is cast to an incompatible function
pointer. In a cast involving function types with a variable argument
list only the types of initial arguments that are provided are
considered. Any parameter of pointer-type matches any other
pointer-type. Any benign differences in integral types are ignored, like
int vs. long on ILP32 targets. Likewise type qualifiers are ignored. The
function type void (*) (void) is special and matches everything, which
can be used to suppress this warning. In a cast involving pointer to
member types this warning warns whenever the type cast is changing the
pointer to member type. This warning is enabled by -Wextra.
```
Reviewed By: rsmith
Differential Revision: https://reviews.llvm.org/D97831
Clang currently automates a fair amount of diagnostic checking for
declaration attributes based on the declarations in Attr.td. It checks
for things like subject appertainment, number of arguments, language
options, etc. This patch uses the same machinery to perform diagnostic
checking on statement attributes.
This would assert if we hit the evaluation step limit between starting
to delay the call and finishing. In any case, delaying the call was
largely pointless as it doesn't really matter when we mark the
evaluation as having had side effects.
This was motivated by the fact that constructor type homing (debug info
optimization that we want to turn on by default) drops some libc++ types,
so an attribute would allow us to override constructor homing and emit
them anyway. I'm currently looking into the particular libc++ issue, but
even if we do fix that, this issue might come up elsewhere and it might be
nice to have this.
As I've implemented it now, the attribute isn't specific to the
constructor homing optimization and overrides all of the debug info
optimizations.
Open to discussion about naming, specifics on what the attribute should do, etc.
Differential Revision: https://reviews.llvm.org/D97411
WG14 adopted N2626 at the meetings this week. This commit adds support
for using ' as a digit separator in a numeric literal which is
compatible with the C++ feature.
This patch extends the matrix spec to allow matrix-by-scalar division.
Originally support for `/` was left out to avoid ambiguity for the
matrix-matrix version of `/`, which could either be elementwise or
specified as matrix multiplication M1 * (1/M2).
For the matrix-scalar version, no ambiguity exists; `*` is also
an elementwise operation in that case. Matrix-by-scalar division
is commonly supported by systems including Matlab, Mathematica
or NumPy.
Reviewed By: rjmccall
Differential Revision: https://reviews.llvm.org/D97857
See https://bugs.llvm.org/show_bug.cgi?id=42154.
GCC's __attribute__((align)) can reduce the alignment of a type when applied to
a typedef. However, functions which take a pointer or reference to the
original type are compiled assuming the original alignment. Therefore when any
such function is passed an object of the new, less-aligned type, an alignment
fault can occur. In particular, this applies to the constructor, which is
defined for the original type and called for the less-aligned object.
This change adds a warning whenever an pointer or reference to an object is
passed to a function that was defined for a more-aligned type.
The calls to ASTContext::getTypeAlignInChars seem change the order in which
record layouts are evaluated, which caused changes to the output of
-fdump-record-layouts. As such some tests needed to be updated:
* Use CHECK-LABEL rather than counting the number of "Dumping AST Record
Layout" headers.
* Check for end of line in labels, so that struct B1 doesn't match struct B
etc.
* Add --strict-whitespace, since the whitespace shows meaningful structure.
* The order in which record layouts are printed has changed in some cases.
* clang-format for regions changed
Differential Revision: https://reviews.llvm.org/D97187
Our diagnostics relating to static assertions were a bit confused. For
instance, when in MS compatibility mode in C (where we accept
static_assert even without including <assert.h>), we would fail
to warn the user that they were using the wrong spelling (even in
pedantic mode), we were missing a compatibility warning about using
_Static_assert in earlier standards modes, diagnostics for the optional
message were not reflected in C as they were in C++, etc.
For ELF targets, GCC 11 will set SHF_GNU_RETAIN on the section of a
`__attribute__((retain))` function/variable to prevent linker garbage
collection. (See AttrDocs.td for the linker support).
This patch adds `retain` functions/variables to the `llvm.used` list, which has
the desired linker GC semantics. Note: `retain` does not imply `used`,
so an unused function/variable can be dropped by Sema.
Before 'retain' was introduced, previous ELF solutions require inline asm or
linker tricks, e.g. `asm volatile(".reloc 0, R_X86_64_NONE, target");`
(architecture dependent) or define a non-local symbol in the section and use
`ld -u`. There was no elegant source-level solution.
With D97448, `__attribute__((retain))` will set `SHF_GNU_RETAIN` on ELF targets.
Differential Revision: https://reviews.llvm.org/D97447
Currently TypePrinter lumps anonymous classes and unnamed classes in one group "anonymous" this is not correct and can be confusing in some contexts.
Differential Revision: https://reviews.llvm.org/D96807
When compiling UEFI applications, the main function is named
efi_main() instead of main(). Let's exclude efi_main() from
-Wmissing-prototypes as well to avoid warnings when working
on UEFI applications.
Differential Revision: https://reviews.llvm.org/D95746
mode.
We use that mode when evaluating ICEs in C, and those shortcuts could
result in ICE evaluation producing the wrong answer, specifically if we
evaluate a statement-expression as part of evaluating the ICE.
Currently TypePrinter lumps anonymous classes and unnamed classes in one group "anonymous" this is not correct and can be confusing in some contexts.
Differential Revision: https://reviews.llvm.org/D96807
Add the types for the RISC-V V extension builtins.
These types will be used by the RISC-V V intrinsics which require
types of the form <vscale x 1 x i64>(LMUL=1 element size=64) or
<vscale x 4 x i32>(LMUL=2 element size=32), etc. The vector_size
attribute does not work for us as it doesn't create a scalable
vector type. We want these types to be opaque and have no operators
defined for them. We want them to be sizeless. This makes them
similar to the ARM SVE builtin types. But we will have quite a bit
more types. This patch adds around 60. Later patches will add
another 230 or so types representing tuples of these types similar
to the x2/x3/x4 types in ARM SVE. But with extra complexity that
these types are combined with the LMUL concept that is unique to
RISCV.
For more background see this RFC
http://lists.llvm.org/pipermail/llvm-dev/2020-October/145850.html
Authored-by: Roger Ferrer Ibanez <roger.ferrer@bsc.es>
Co-Authored-by: Hsiangkai Wang <kai.wang@sifive.com>
Differential Revision: https://reviews.llvm.org/D92715
if E is merely instantiation-dependent."
This change leaves us unable to distinguish between different function
templates that differ in only instantiation-dependent ways, for example
template<typename T> decltype(int(T())) f();
template<typename T> decltype(int(T(0))) f();
We'll need substantially better support for types that are
instantiation-dependent but not dependent before we can go ahead with
this change.
This reverts commit e3065ce238.
if E is merely instantiation-dependent.
Previously reverted in 34e72a146111dd986889a0f0ec8767b2ca6b2913;
re-committed with a fix to an issue that caused name mangling to assert.
The `-Wpointer-sign` warning text is inappropriate for describing the
incompatible pointer conversion between plain `char` and explicitly
`signed`/`unsigned` `char` (whichever plain `char` has the same range
as) and vice versa.
Specifically, in part, it reads "converts between pointers to integer
types with different sign". This patch changes that portion to read
instead as "converts between pointers to integer types where one is of
the unique plain 'char' type and the other is not" when one of the types
is plain `char`.
C17 subclause 6.5.16.1 indicates that the conversions resulting in
`-Wpointer-sign` warnings in assignment-like contexts are constraint
violations. This means that strict conformance requires a diagnostic for
the case where the message text is wrong before this patch. The lack of
an even more specialized warning group is consistent with GCC.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D93999
Introduce a function attribute 'enforce_tcb' that prevents the function
from calling other functions without the same attribute. This allows
isolating code that's considered to be somehow privileged so that it could not
use its privileges to exhibit arbitrary behavior.
Introduce an on-by-default warning '-Wtcb-enforcement' that warns
about violations of the above rule.
Introduce a function attribute 'enforce_tcb_leaf' that suppresses
the new warning within the function it is attached to. Such leaf functions
may implement common functionality between the trusted and the untrusted code
but they require extra careful audit with respect to their capabilities.
Fixes after a revert in 419ef38a50293c58078f830517f5e305068dbee6:
Fix a test.
Add workaround for GCC bug (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67274).
Attribute the patch appropriately!
Differential Revision: https://reviews.llvm.org/D91898
Introduce a function attribute 'enforce_tcb' that prevents the function
from calling other functions without the same attribute. This allows
isolating code that's considered to be somehow privileged so that it could not
use its privileges to exhibit arbitrary behavior.
Introduce an on-by-default warning '-Wtcb-enforcement' that warns
about violations of the above rule.
Introduce a function attribute 'enforce_tcb_leaf' that suppresses
the new warning within the function it is attached to. Such leaf functions
may implement common functionality between the trusted and the untrusted code
but they require extra careful audit with respect to their capabilities.
Differential Revision: https://reviews.llvm.org/D91898
This patch renames PackStack and related variable names to also contain align across Clang.
As it is right now, Clang already uses one stack to record the information from both #pragma
align and #pragma pack. Leaving it as PackStack is confusing, and could cause people to
ignore #pragma align when developing code that interacts with PackStack.
Differential Revision: https://reviews.llvm.org/D93901
We supports SjLj exception handling in the backend, so changing
clang to allow lowering using SjLj exceptions. Update a regression
test also.
Reviewed By: simoll
Differential Revision: https://reviews.llvm.org/D94076
We currently reject this valid C construct by claiming it declares a
non-local variable: for (struct { int i; } s={0}; s.i != 0; s.i--) ;
We expected all declaration in the clause-1 declaration statement to be
a local VarDecl, but there can be other declarations involved such as a
tag declaration. This fixes PR35757.
On PPC, the vector pair instructions are independent from MMA.
This patch renames the vector pair LLVM intrinsics and Clang builtins to replace the _mma_ prefix by _vsx_ in their names.
We also move the vector pair type/intrinsic/builtin tests to their own files.
Differential Revision: https://reviews.llvm.org/D91974
If two variables are declared with __attribute__((section(name))) and
the implicit section types (e.g. read only vs writeable) conflict, an
error is raised. Extend this mechanism so that an error is raised if the
section type implied by a function's __attribute__((section)) conflicts
with that of another variable.
The `assume` attribute is a way to provide additional, arbitrary
information to the optimizer. For now, assumptions are restricted to
strings which will be accumulated for a function and emitted as comma
separated string function attribute. The key of the LLVM-IR function
attribute is `llvm.assume`. Similar to `llvm.assume` and
`__builtin_assume`, the `assume` attribute provides a user defined
assumption to the compiler.
A follow up patch will introduce an LLVM-core API to query the
assumptions attached to a function. We also expect to add more options,
e.g., expression arguments, to the `assume` attribute later on.
The `omp [begin] asssumes` pragma will leverage this attribute and
expose the functionality in the absence of OpenMP.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D91979
... and give more guidance to users.
If specifying -msve-vector-bits on a non-SVE target, clang would say:
error: '-msve-vector-bits' is not supported without SVE enabled
1. The driver lacks logic for "implied features".
This would result in this error being raised for -march=...+sve2,
even though +sve2 implies +sve.
2. Feature implication is well modelled in LLVM, so push the error down
the stack.
3. Hint to the user what flag they need to consider setting.
Now clang fails later, when the feature is used, saying:
aarch64-sve-vector-bits.c:42:41: error: 'arm_sve_vector_bits' attribute is not supported on targets missing 'sve'; specify an appropriate -march= or -mcpu=
typedef svint32_t noflag __attribute__((arm_sve_vector_bits(256)));
Move clang/test/Sema/{neon => arm}-vector-types-support.c and put tests for
this warning together in one place.
Reviewed By: sdesmalen
Differential Revision: https://reviews.llvm.org/D92487
552c6c2 removed support for promoting VLAs to constant arrays when the bounds
isn't an ICE, since this can result in miscompiling a conforming program that
assumes that the array is a VLA. Promoting VLAs for fields is still supported,
since clang doesn't support VLAs in fields, so no conforming program could have
a field VLA.
This change is really disruptive, so this commit carves out two more cases
where we promote VLAs which can't miscompile a conforming program:
- When the VLA appears in an ivar -- this seems like a corollary to the field thing
- When the VLA has an initializer -- VLAs can't have an initializer
Differential revision: https://reviews.llvm.org/D90871
Similar to Windows Itanium, PS4 is also an Itanium C++ ABI variant
which shares the goal of semantic compatibility with Microsoft C++
code that uses dllimport/export.
This change introduces a new function to determine from the triple
if an environment aims for compatibility with MS C++ code w.r.t to
these attributes and guards the relevant code paths using that
function.
Differential Revision: https://reviews.llvm.org/D90299
This patch adds tests for things that happened to be fixed by previous
patches, but that should continue working if we do decide to treat
sizeless types as incomplete types.
Differential Revision: https://reviews.llvm.org/D79584
Previously, lax conversions were only allowed between SVE vector-length
agnostic types and vector-length specific types. This meant that code
such as the following:
#include <arm_sve.h>
#define N __ARM_FEATURE_SVE_BITS
#define FIXED_ATTR __attribute__ ((vector_size (N/8)))
typedef float fixed_float32_t FIXED_ATTR;
void foo() {
fixed_float32_t fs32;
svfloat64_t s64;
fs32 = s64;
}
was not allowed.
This patch makes a minor change to areLaxCompatibleSveTypes to allow for
lax conversions to be performed between SVE vector-length agnostic types
and GNU vectors.
Differential Revision: https://reviews.llvm.org/D91696
The dependency mechanism for C has been implemented, and we have rolled out
this to all internal users, didn't see crashy issues, we consider it is stable
enough.
Differential Revision: https://reviews.llvm.org/D89046
This patch allows C-style casting between fixed-size and scalable
vectors. This kind of cast was previously blocked by the compiler, but
it should be allowed.
Differential Revision: https://reviews.llvm.org/D91262
Lax vector conversions was behaving incorrectly for implicit casts
between scalable and fixed-length vector types. For example, this:
#include <arm_sve.h>
#define N __ARM_FEATURE_SVE_BITS
#define FIXED_ATTR __attribute__((arm_sve_vector_bits(N)))
typedef svfloat32_t fixed_float32_t FIXED_ATTR;
void allowed_depending() {
fixed_float32_t fs32;
svfloat64_t s64;
fs32 = s64;
}
... would fail because the vectors have differing lane sizes. This patch
implements the correct behaviour for
-flax-vector-conversions={none,all,integer}. Specifically:
- -flax-vector-conversions=none prevents all lax vector conversions
between scalable and fixed-sized vectors.
- -flax-vector-conversions=integer allows lax vector conversions between
scalable and fixed-size vectors whose element types are integers.
- -flax-vector-conversions=all allows all lax vector conversions between
scalable and fixed-size vectors (including those with floating point
element types).
The implicit conversions are implemented as bitcasts.
Reviewed By: fpetrogalli
Differential Revision: https://reviews.llvm.org/D91067
Adapt the declarations of `svpattern` and `svprfop` to the most recent
one defined in section "5. Enum declarations" of the SVE ACLE
specifications [1].
The signature of the intrinsics using these enums have been changed
accordingly.
A test has been added to make sure that `svpattern` and `svprfop` are
not typedefs.
[1] https://developer.arm.com/documentation/100987/latest, version
00bet6
Reviewed By: joechrisellis
Differential Revision: https://reviews.llvm.org/D91333
As Richard Smith pointed out in the review of D90123, both the C and C++
standard call it lvalue and rvalue, so let's stick to the same spelling
in Clang.
The use of the new types introduced for PowerPC MMA instructions needs to be restricted.
We add a PowerPC function checking that the given type is valid in a context in which we don't allow MMA types.
This function is called from various places in Sema where we want to prevent the use of these types.
Differential Revision: https://reviews.llvm.org/D82035
This patch adds tests and support for operations on SVE vectors created
by the 'arm_sve_vector_bits' attribute, described by the Arm C Language
Extensions (ACLE, version 00bet6, section 3.7.3.3) for SVE [1].
This covers the following:
* VLSTs support the same forms of element-wise initialization as GNU
vectors.
* VLSTs support the same built-in C and C++ operators as GNU vectors.
* Conditional and binary expressions containing GNU and SVE vectors
(fixed or sizeless) are invalid since the ambiguity around the result
type affects the ABI.
No functional changes were required to support vector initialization and
operators. The functional changes are to address unsupported conditional and
binary expressions.
[1] https://developer.arm.com/documentation/100987/latest
Reviewed By: fpetrogalli
Differential Revision: https://reviews.llvm.org/D88233
Checks to make sure that stdlib's (std::)free is being appropriately
used. Presently checks for the following misuses:
- free(&stack_object)
- free(stack_array)
Differential Revision: https://reviews.llvm.org/D89988
This allows using annotation in a much more contexts than it currently has.
especially when annotation with template or constexpr.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D88645
for which it matters.
This is a step towards separating checking for a constant initializer
(in which std::is_constant_evaluated returns true) and any other
evaluation of a variable initializer (in which it returns false).
Old GCC used to aggressively fold VLAs to constant-bound arrays at block
scope in GNU mode. That's non-conforming, and more modern versions of
GCC only do this at file scope. Update Clang to do the same.
Also promote the warning for this from off-by-default to on-by-default
in all cases; more recent versions of GCC likewise warn on this by
default.
This is still slightly more permissive than GCC, as pointed out in
PR44406, as we still fold VLAs to constant arrays in structs, but that
seems justifiable given that we don't support VLA-in-struct (and don't
intend to ever support it), but GCC does.
Differential Revision: https://reviews.llvm.org/D89523
Michael Benfield