There are many issues that popped up with the counted_by feature. The
patch #73730 has grown too large and approval is blocking Linux testing.
Includes reverts of:
commit 769bc11f684d ("[Clang] Implement the 'counted_by' attribute
(#68750)")
commit bc09ec696209 ("[CodeGen] Revamp counted_by calculations
(#70606)")
commit 1a09cfb2f35d ("[Clang] counted_by attr can apply only to C99
flexible array members (#72347)")
commit a76adfb992c6 ("[NFC][Clang] Refactor code to calculate flexible
array member size (#72790)")
commit d8447c78ab16 ("[Clang] Correct handling of negative and
out-of-bounds indices (#71877)")
Partial commit b31cd07de5b7 ("[Clang] Regenerate test checks (NFC)")
Closes#73168Closes#75173
The new attribute can be placed on statements in order to suppress
arbitrary warnings produced by static analysis tools at those statements.
Previously such suppressions were implemented as either informal comments
(eg. clang-tidy `// NOLINT:`) or with preprocessor macros (eg.
clang static analyzer's `#ifdef __clang_analyzer__`). The attribute
provides a universal, formal, flexible and neat-looking suppression mechanism.
Implement support for the new attribute in the clang static analyzer;
clang-tidy coming soon.
The attribute allows specifying which specific warnings to suppress,
in the form of free-form strings that are intended to be specific to
the tools, but currently none are actually supported; so this is also
going to be a future improvement.
Differential Revision: https://reviews.llvm.org/D93110
This patch replaces uses of StringRef::{starts,ends}with with
StringRef::{starts,ends}_with for consistency with
std::{string,string_view}::{starts,ends}_with in C++20.
I'm planning to deprecate and eventually remove
StringRef::{starts,ends}with.
This commit introduces support for the MSVC-specific C++11-style
attribute `[[msvc::constexpr]]`, which was introduced in MSVC 14.33.
The semantics of this attribute are enabled only under
MSVC compatibility (`-fms-compatibility-version`) 14.33 and higher.
Additionally, the default value of `_MSC_VER` has been raised to 1433.
The current implementation lacks support for:
- `[[msvc::constexpr]]` constructors (see #72149);
at the time of this implementation, such support would have required
an unreasonable number of changes in Clang.
- `[[msvc::constexpr]] return ::new` (constexpr placement new) from
non-std namespaces (see #74924).
Relevant to: #57696
This commit adds a new BPF specific structure attribte
`__attribute__((preserve_static_offset))` and a pass to deal with it.
This attribute may be attached to a struct or union declaration, where
it notifies the compiler that this structure is a "context" structure.
The following limitations apply to context structures:
- runtime environment might patch access to the fields of this type by
updating the field offset;
BPF verifier limits access patterns allowed for certain data
types. E.g. `struct __sk_buff` and `struct bpf_sock_ops`. For these
types only `LD/ST <reg> <static-offset>` memory loads and stores are
allowed.
This is so because offsets of the fields of these structures do not
match real offsets in the running kernel. During BPF program
load/verification loads and stores to the fields of these types are
rewritten so that offsets match real offsets. For this rewrite to
happen static offsets have to be encoded in the instructions.
See `kernel/bpf/verifier.c:convert_ctx_access` function in the Linux
kernel source tree for details.
- runtime environment might disallow access to the field of the type
through modified pointers.
During BPF program verification a tag `PTR_TO_CTX` is tracked for
register values. In case if register with such tag is modified BPF
programs are not allowed to read or write memory using register. See
kernel/bpf/verifier.c:check_mem_access function in the Linux kernel
source tree for details.
Access to the structure fields is translated to IR as a sequence:
- `(load (getelementptr %ptr %offset))` or
- `(store (getelementptr %ptr %offset))`
During instruction selection phase such sequences are translated as a
single load instruction with embedded offset, e.g. `LDW %ptr, %offset`,
which matches access pattern necessary for the restricted
set of types described above (when `%offset` is static).
Multiple optimizer passes might separate these instructions, this
includes:
- SimplifyCFGPass (sinking)
- InstCombine (sinking)
- GVN (hoisting)
The `preserve_static_offset` attribute marks structures for which the
following transformations happen:
- at the early IR processing stage:
- `(load (getelementptr ...))` replaced by call to intrinsic
`llvm.bpf.getelementptr.and.load`;
- `(store (getelementptr ...))` replaced by call to intrinsic
`llvm.bpf.getelementptr.and.store`;
- at the late IR processing stage this modification is undone.
Such handling prevents various optimizer passes from generating
sequences of instructions that would be rejected by BPF verifier.
The __attribute__((preserve_static_offset)) has a priority over
__attribute__((preserve_access_index)). When preserve_access_index
attribute is present preserve access index transformations are not
applied.
This addresses the issue reported by the following thread:
https://lore.kernel.org/bpf/CAA-VZPmxh8o8EBcJ=m-DH4ytcxDFmo0JKsm1p1gf40kS0CE3NQ@mail.gmail.com/T/#m4b9ce2ce73b34f34172328f975235fc6f19841b6
This is a second attempt to commit this change, previous reverted
commit is: cb13e9286b6d4e384b5d4203e853d44e2eff0f0f.
The following items had been fixed:
- test case bpf-preserve-static-offset-bitfield.c now uses
`-triple bpfel` to avoid different codegen for little/big endian
targets.
- BPFPreserveStaticOffset.cpp:removePAICalls() modified to avoid
use after free for `WorkList` elements `V`.
Differential Revision: https://reviews.llvm.org/D133361
This commit adds a new BPF specific structure attribte
`__attribute__((preserve_static_offset))` and a pass to deal with it.
This attribute may be attached to a struct or union declaration, where
it notifies the compiler that this structure is a "context" structure.
The following limitations apply to context structures:
- runtime environment might patch access to the fields of this type by
updating the field offset;
BPF verifier limits access patterns allowed for certain data
types. E.g. `struct __sk_buff` and `struct bpf_sock_ops`. For these
types only `LD/ST <reg> <static-offset>` memory loads and stores are
allowed.
This is so because offsets of the fields of these structures do not
match real offsets in the running kernel. During BPF program
load/verification loads and stores to the fields of these types are
rewritten so that offsets match real offsets. For this rewrite to
happen static offsets have to be encoded in the instructions.
See `kernel/bpf/verifier.c:convert_ctx_access` function in the Linux
kernel source tree for details.
- runtime environment might disallow access to the field of the type
through modified pointers.
During BPF program verification a tag `PTR_TO_CTX` is tracked for
register values. In case if register with such tag is modified BPF
programs are not allowed to read or write memory using register. See
kernel/bpf/verifier.c:check_mem_access function in the Linux kernel
source tree for details.
Access to the structure fields is translated to IR as a sequence:
- `(load (getelementptr %ptr %offset))` or
- `(store (getelementptr %ptr %offset))`
During instruction selection phase such sequences are translated as a
single load instruction with embedded offset, e.g. `LDW %ptr, %offset`,
which matches access pattern necessary for the restricted
set of types described above (when `%offset` is static).
Multiple optimizer passes might separate these instructions, this
includes:
- SimplifyCFGPass (sinking)
- InstCombine (sinking)
- GVN (hoisting)
The `preserve_static_offset` attribute marks structures for which the
following transformations happen:
- at the early IR processing stage:
- `(load (getelementptr ...))` replaced by call to intrinsic
`llvm.bpf.getelementptr.and.load`;
- `(store (getelementptr ...))` replaced by call to intrinsic
`llvm.bpf.getelementptr.and.store`;
- at the late IR processing stage this modification is undone.
Such handling prevents various optimizer passes from generating
sequences of instructions that would be rejected by BPF verifier.
The __attribute__((preserve_static_offset)) has a priority over
__attribute__((preserve_access_index)). When preserve_access_index
attribute is present preserve access index transformations are not
applied.
This addresses the issue reported by the following thread:
https://lore.kernel.org/bpf/CAA-VZPmxh8o8EBcJ=m-DH4ytcxDFmo0JKsm1p1gf40kS0CE3NQ@mail.gmail.com/T/#m4b9ce2ce73b34f34172328f975235fc6f19841b6
Differential Revision: https://reviews.llvm.org/D133361
This change implements parsing for HLSL's parameter modifier keywords
`in`, `out` and `inout`. Because HLSL doesn't support references or
pointers, these keywords are used to allow parameters to be passed in
and out of functions.
This change only implements the parsing and AST support. In the HLSL
ASTs we represent `out` and `inout` parameters as references, and we
implement the semantics of by-value passing during IR generation.
In HLSL parameters marked `out` and `inout` are ambiguous in function
declarations, and `in`, `out` and `inout` may be ambiguous at call
sites.
This means a function may be defined as `fn(in T)` and `fn(inout T)` or
`fn(out T)`, but not `fn(inout T)` and `fn(out T)`. If a funciton `fn`
is declared with `in` and `inout` or `out` arguments, the call will be
ambiguous the same as a C++ call would be ambiguous given declarations
`fn(T)` and `fn(T&)`.
Fixes#59849
Ensure that we're dealing only with C99 flexible array members. I.e.
ones with incomplete types:
struct s {
int count;
char array[]; /* note: no size specified */
};
Authored-by: Bill Wendling <isanbard@gmail.com>
This attribute allows user to specify type of the bitfield that will be
emitted to debug info without affecting semantics of the program. Since
it doesn't affect semantics, this attribute can be safely ignored by
other compilers.
This is useful when user is forced to use the same type for all
bitfields in a class to get better
[layout](https://godbolt.org/z/ovWqzqv9x) and
[codegen](https://godbolt.org/z/bdoqvz9e6) from MSVC, because it allows
debuggers to interpret the value of bitfield in the most human-friendly
way (e.g. when value actually comes from an enum). This is driven by my
work on LLDB formatters for Clang. I have two use cases for this:
```cpp
namespace Clang {
class Type {
enum TypeClass { ... };
struct TypeBitfields {
[[clang::preferred_type(clang::Type::TypeClass)]] unsigned TC: 8;
[[clang::preferred_type(bool)]] mutable unsigned FromAST : 1;
};
};
}
```
This patch adds `CC_M68kRTD`, which will be used on function if either
`__attribute__((m68k_rtd))` is presented or `-mrtd` flag is given.
Differential Revision: https://reviews.llvm.org/D149867
The 'counted_by' attribute is used on flexible array members. The
argument for the attribute is the name of the field member in the same
structure holding the count of elements in the flexible array. This
information can be used to improve the results of the array bound
sanitizer and the '__builtin_dynamic_object_size' builtin.
This example specifies the that the flexible array member 'array' has
the number of elements allocated for it in 'count':
struct bar;
struct foo {
size_t count;
/* ... */
struct bar *array[] __attribute__((counted_by(count)));
};
This establishes a relationship between 'array' and 'count',
specifically that 'p->array' must have *at least* 'p->count' number of
elements available. It's the user's responsibility to ensure that this
relationship is maintained through changes to the structure.
In the following, the allocated array erroneously has fewer elements
than what's specified by 'p->count'. This would result in an
out-of-bounds access not not being detected:
struct foo *p;
void foo_alloc(size_t count) {
p = malloc(MAX(sizeof(struct foo),
offsetof(struct foo, array[0]) + count *
sizeof(struct bar *)));
p->count = count + 42;
}
The next example updates 'p->count', breaking the relationship
requirement that 'p->array' must have at least 'p->count' number of
elements available:
struct foo *p;
void foo_alloc(size_t count) {
p = malloc(MAX(sizeof(struct foo),
offsetof(struct foo, array[0]) + count *
sizeof(struct bar *)));
p->count = count + 42;
}
void use_foo(int index) {
p->count += 42;
p->array[index] = 0; /* The sanitizer cannot properly check this access */
}
Reviewed By: nickdesaulniers, aaron.ballman
Differential Revision: https://reviews.llvm.org/D148381
Functions with these attributes will be automatically called before
main() or after main() exits gracefully. In glibc environments, the
constructor function is passed the same arguments as main(), so that
signature is allowed. In all other environments, we require the function
to accept no arguments and either return `void` or `int`. The functions
must use the C calling convention. In C++ language modes, the functions
cannot be a nonstatic member function, or a consteval function.
Additionally, these reuse the same priority logic as the init_priority
attribute which explicitly reserved priorty values <= 100 or > 65535. So
we now diagnose use of reserved priorities the same as we do for the
init_priority attribute, but we downgrade the error to be a warning
which defaults to an error to ease use for implementers like compiler-rt
or libc.
This relands a633a3761fcbd0799426cbf5fbd7794961080e43 with fixes.
Functions with these attributes will be automatically called before
main() or after main() exits gracefully. In glibc environments, the
constructor function is passed the same arguments as main(), so that
signature is allowed. In all other environments, we require the function
to accept no arguments and either return `void` or `int`. The functions
must use the C calling convention. In C++ language modes, the functions
cannot be a nonstatic member function, or a consteval function.
Additionally, these reuse the same priority logic as the init_priority
attribute which explicitly reserved priorty values <= 100 or > 65535. So
we now diagnose use of reserved priorities the same as we do for the
init_priority attribute, but we downgrade the error to be a warning
which defaults to an error to ease use for implementers like compiler-rt
or libc.
This relands b4435104ca3904529723b0673cc0f624cf8c54e6 with fixes.
This reverts commit 9a954c693573281407f6ee3f4eb1b16cc545033d, which
causes clang crashes when compiling with `-fsanitize=bounds`. See
9a954c6935 (commitcomment-129529574)
for details.
The 'counted_by' attribute is used on flexible array members. The
argument for the attribute is the name of the field member in the same
structure holding the count of elements in the flexible array. This
information can be used to improve the results of the array bound sanitizer
and the '__builtin_dynamic_object_size' builtin.
This example specifies the that the flexible array member 'array' has the
number of elements allocated for it in 'count':
struct bar;
struct foo {
size_t count;
/* ... */
struct bar *array[] __attribute__((counted_by(count)));
};
This establishes a relationship between 'array' and 'count', specifically
that 'p->array' must have *at least* 'p->count' number of elements available.
It's the user's responsibility to ensure that this relationship is maintained
through changes to the structure.
In the following, the allocated array erroneously has fewer elements than
what's specified by 'p->count'. This would result in an out-of-bounds access not
not being detected:
struct foo *p;
void foo_alloc(size_t count) {
p = malloc(MAX(sizeof(struct foo),
offsetof(struct foo, array[0]) + count *
sizeof(struct bar *)));
p->count = count + 42;
}
The next example updates 'p->count', breaking the relationship requirement that
'p->array' must have at least 'p->count' number of elements available:
struct foo *p;
void foo_alloc(size_t count) {
p = malloc(MAX(sizeof(struct foo),
offsetof(struct foo, array[0]) + count *
sizeof(struct bar *)));
p->count = count + 42;
}
void use_foo(int index) {
p->count += 42;
p->array[index] = 0; /* The sanitizer cannot properly check this access */
}
Reviewed By: nickdesaulniers, aaron.ballman
Differential Revision: https://reviews.llvm.org/D148381
This implements the [[msvc::no_unique_address]] attribute.
There is not ABI compatibility in this patch because the attribute is
relatively new and there's still some uncertainty in the MSVC version.
The recommit changes the attribute definitions so that instead of making
two separate attributes for no_unique_address
and msvc::no_unique_address, it modifies the attributes tablegen emitter
to allow spellings to be target-specific.
This reverts commit 71f9e7695b87298f9855d8890f0e6a3b89381eb5.
This reverts commit b4435104ca3904529723b0673cc0f624cf8c54e6.
This caused too many disruptions in compiler-rt where reserved
priorities were being used. Reverting to investigate appropriate
solutions.
Functions with these attributes will be automatically called before
`main()` or after `main()` exits gracefully, which means the functions
should not accept arguments or have a returned value (nothing can
provide an argument to the call in these cases, and nothing can use the
returned value), nor should they be allowed on a non-static member
function or consteval function in C++. We allow 'int' as a return type for
the function due to finding a significant amount of historical code using
`int(void)` as a signature.
Additionally, these reuse the same priority logic as the init_priority
attribute which explicitly reserved priorty values <= 100 or > 65535. So
we now diagnose use of reserved priorities the same as we do for the
init_priority attribute.
This reverts commit 4a55d426967b9c70f5dea7b3a389e11393a4f4c4.
Reverting because this breaks sphinx documentation, and even with it
fixed the format of the attribute makes the no_unique_address
documentation show up twice.
https://reviews.llvm.org/D158247 caused regressions for HIP on Windows
and was reverted.
A reduced test case is:
```
typedef void (__stdcall* funcTy)();
void invoke(funcTy f);
static void __stdcall callee() noexcept {
}
void foo() {
invoke(callee);
}
```
It is due to clang missing handling host/device attributes for calling
convention at a few places
This patch fixes that.
The goal of this change is to clean up some of the code surrounding
HLSL using CXXThisExpr as a non-pointer l-value. This change cleans up
a bunch of assumptions and inconsistencies around how the type of
`this` is handled through the AST and code generation.
This change is be mostly NFC for HLSL, and completely NFC for other
language modes.
This change introduces a new member to query for the this object's type
and seeks to clarify the normal usages of the this type.
With the introudction of HLSL to clang, CXXThisExpr may now be an
l-value and behave like a reference type rather than C++'s normal
method of it being an r-value of pointer type.
With this change there are now three ways in which a caller might need
to query the type of `this`:
* The type of the `CXXThisExpr`
* The type of the object `this` referrs to
* The type of the implicit (or explicit) `this` argument
This change codifies those three ways you may need to query
respectively as:
* CXXMethodDecl::getThisType()
* CXXMethodDecl::getThisObjectType()
* CXXMethodDecl::getThisArgType()
This change then revisits all uses of `getThisType()`, and in cases
where the only use was to resolve the pointee type, it replaces the
call with `getThisObjectType()`. In other cases it evaluates whether
the desired returned type is the type of the `this` expr, or the type
of the `this` function argument. The `this` expr type is used for
creating additional expr AST nodes and for member lookup, while the
argument type is used mostly for code generation.
Additionally some cases that used `getThisType` in simple queries could
be substituted for `getThisObjectType`. Since `getThisType` is
implemented in terms of `getThisObjectType` calling the later should be
more efficient if the former isn't needed.
Reviewed By: aaron.ballman, bogner
Differential Revision: https://reviews.llvm.org/D159247
This reverts commit de0df639724b10001ea9a74539381ea494296be9.
It was reverted due to regression in HIP unit test on Windows:
In file included from C:\hip-tests\catch\unit\graph\hipGraphClone.cc:37:
In file included from C:\hip-tests\catch\.\include\hip_test_common.hh:24:
In file included from C:\hip-tests\catch\.\include/hip_test_context.hh:24:
In file included from C:/install/native/Release/x64/hip/include\hip/hip_runtime.h:54:
C:/dk/win\vc\14.31.31107\include\thread:76:70: error: cannot initialize a parameter of type '_beginthreadex_proc_type' (aka 'unsigned int (*)(void *) __attribute__((stdcall))') with an lvalue of type 'const unsigned int (*)(void *) noexcept __attribute__((stdcall))': different exception specifications
76 | reinterpret_cast<void*>(_CSTD _beginthreadex(nullptr, 0, _Invoker_proc, _Decay_copied.get(), 0, &_Thr._Id));
| ^~~~~~~~~~~~~
C:\hip-tests\catch\unit\graph\hipGraphClone.cc:290:21) &>' requested here
90 | _Start(_STD forward<_Fn>(_Fx), _STD forward<_Args>(_Ax)...);
| ^
C:\hip-tests\catch\unit\graph\hipGraphClone.cc:290:21) &, 0>' requested here
311 | std::thread t(lambdaFunc);
| ^
C:/dk/win\ms_wdk\e22621\Include\10.0.22621.0\ucrt\process.h:99:40: note: passing argument to parameter '_StartAddress' here
99 | _In_ _beginthreadex_proc_type _StartAddress,
| ^
1 error generated when compiling for gfx1030.
This moves the sema checking of the entrypoint sensitive HLSL
attributes all into one place. This ended up being kind of large for a
couple of reasons:
- I had to move the call to CheckHLSLEntryPoint later in
ActOnFunctionDeclarator so that we do this after redeclarations and
have access to all of the attributes.
- We need to transfer the target shader stage onto the specified entry
point before doing the checking.
- I removed "library" from the HLSLShader attribute value enum and
just go through a string to convert from the triple - the other way
was confusing and brittle.
Differential Revision: https://reviews.llvm.org/D158803
Currently, clang does not resolve certain overloaded functions correctly in the initializer
of global variables, e.g.
template<typename T1, typename U>
T1 mypow(T1, U);
__attribute__((device)) double mypow(double, int);
double t_extent = mypow(1.0, 2);
In the above example, mypow is supposed to resolve to the host version
but clang resolves it to the device version instead, and emits an error
(https://godbolt.org/z/17xxzaa67).
However, if the variable is assigned in a host function, there is no error.
The discrepancy in overloading resolution inside and outside of
a function is due to clang not accounting for the host/device target
when resolving functions called in the initializer of a global variable.
This patch introduces a global host/device target context for CUDA/HIP
for functions called outside of functions. For global variable initialization,
it is determined by the host/device attribute of the variable. For other
situations, a default value of host_device is sufficient.
Reviewed by: Artem Belevich
Differential Revision: https://reviews.llvm.org/D158247
Fixes: SWDEV-416731
The attributes changes were left out of Clang 17.
Attributes that used to take a string literal now accept an unevaluated
string literal instead, which means they reject numeric escape sequences
and strings literal with an encoding prefix - but the later was already
ill-formed in most cases.
We need to know that we are going to parse an unevaluated string literal
before we do - so we can reject numeric escape sequence,
so we derive from Attrs.td which attributes parameters are expected
to be string literals.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D156237
This does the rename for most internal uses of C2x, but does not rename
or reword diagnostics (those will be done in a follow-up).
I also updated standards references and citations to the final wording
in the standard.
This patch adds all the language-level function keywords defined in:
https://github.com/ARM-software/acle/pull/188 (merged)
https://github.com/ARM-software/acle/pull/261 (update after D148700 landed)
The keywords are used to control PSTATE.ZA and PSTATE.SM, which are
respectively used for enabling the use of the ZA matrix array and Streaming
mode. This information needs to be available on call sites, since the use
of ZA or streaming mode may have to be enabled or disabled around the
call-site (depending on the IR attributes set on the caller and the
callee). For calls to functions from a function pointer, there is no IR
declaration available, so the IR attributes must be added explicitly to the
call-site.
With the exception of '__arm_locally_streaming' and '__arm_new_za' the
information is part of the function's interface, not just the function
definition, and thus needs to be propagated through the
FunctionProtoType::ExtProtoInfo.
This patch adds the defintions of these keywords, as well as codegen and
semantic analysis to ensure conversions between function pointers are valid
and that no conflicting keywords are set. For example, '__arm_streaming'
and '__arm_streaming_compatible' are mutually exclusive.
Differential Revision: https://reviews.llvm.org/D127762
The patch in D155211 added basic support for the `.alias` keyword in
PTX. This means we should be able to permit use of this in clang.
Reviewed By: tra
Differential Revision: https://reviews.llvm.org/D156014
This reverts commit 0d12683046ca75fb08e285f4622f2af5c82609dc and
reapplies ef9ec4bbcca2fa4f64df47bc426f1d1c59ea47e2 with an extension to
fix the Flang build.
Differential Revision: https://reviews.llvm.org/D156184
CUDA and HIP have kernel attributes to tune the code generation (in the
backend). To reuse this functionality for OpenMP target regions we
introduce the `ompx_attribute` clause that takes these kernel
attributes and emits code as if they had been attached to the kernel
fuction (which is implicitly generated).
To limit the impact, we only support three kernel attributes:
`amdgpu_waves_per_eu`, for AMDGPU
`amdgpu_flat_work_group_size`, for AMDGPU
`launch_bounds`, for NVPTX
The existing implementations of those attributes are used for error
checking and code generation. `ompx_attribute` can be attached to any
executable target region and it can hold more than one kernel attribute.
Differential Revision: https://reviews.llvm.org/D156184
Allow specifying 'nomerge' attribute for function pointers,
e.g. like in the following C code:
extern void (*foo)(void) __attribute__((nomerge));
void bar(long i) {
if (i)
foo();
else
foo();
}
With the goal to attach 'nomerge' to both calls done through 'foo':
@foo = external local_unnamed_addr global ptr, align 8
define dso_local void @bar(i64 noundef %i) local_unnamed_addr #0 {
; ...
%0 = load ptr, ptr @foo, align 8, !tbaa !5
; ...
if.then:
tail call void %0() #1
br label %if.end
if.else:
tail call void %0() #1
br label %if.end
if.end:
ret void
}
; ...
attributes #1 = { nomerge ... }
Report a warning in case if 'nomerge' is specified for a variable that
is not a function pointer, e.g.:
t.c:2:22: warning: 'nomerge' attribute is ignored because 'j' is not a function pointer [-Wignored-attributes]
2 | int j __attribute__((nomerge));
| ^
The intended use-case is for BPF backend.
BPF provides a sort of "standard library" functions that are called
helpers. BPF also verifies usage of these helpers before program
execution. Because of limitations of verification / runtime model it
is important to keep calls to some of such helpers from merging.
An example could be found by the link [1], there input C code:
if (data_end - data > 1024) {
bpf_for_each_map_elem(&map1, cb, &cb_data, 0);
} else {
bpf_for_each_map_elem(&map2, cb, &cb_data, 0);
}
Is converted to bytecode equivalent to:
if (data_end - data > 1024)
tmp = &map1;
else
tmp = &map2;
bpf_for_each_map_elem(tmp, cb, &cb_data, 0);
However, BPF verification/runtime requires to use the same map address
for each particular `bpf_for_each_map_elem()` call.
The 'nomerge' attribute is a perfect match for this situation, but
unfortunately BPF helpers are declared as pointers to functions:
static long (*bpf_for_each_map_elem)(void *map, ...) = (void *) 164;
Hence, this commit, allowing to use 'nomerge' for function pointers.
[1] https://lore.kernel.org/bpf/03bdf90f-f374-1e67-69d6-76dd9c8318a4@meta.com/
Differential Revision: https://reviews.llvm.org/D152986
This patch relaxes the front end AIX diagnostics added in D102070 to accept the
local-exec TLS model, as we plan to support this model in a series of future patches.
The diagnostics are relaxed when local-exec is used as a compiler option to
`-ftls-model=*` and in the `__attribute__((tls_model("local-exec")))` attribute.
Differential Revision: https://reviews.llvm.org/D149596
