This fixes some minor grammatical issues I noticed when reading the docs, and changes the recommended feature testing approach to use __has_attribute instead of __has_extension.
llvm-svn: 369687
Summary:
Previously __has_builtin(__builtin_*) would return false for
__builtin_*s that we modeled as keywords rather than as functions
(because they take type arguments). With this patch, all builtins
that are called with function-call-like syntax return true from
__has_builtin (covering __builtin_* and also the __is_* and __has_* type
traits and the handful of similar builtins without such a prefix).
Update the documentation on __has_builtin and on type traits to match.
While doing this I noticed the type trait documentation was out of date
and incomplete; that's fixed here too.
Reviewers: aaron.ballman
Subscribers: jfb, kristina, cfe-commits
Tags: #clang
Differential Revision: https://reviews.llvm.org/D66100
llvm-svn: 368785
Rename lang mode flag to -cl-std=clc++/-cl-std=CLC++
or -std=clc++/-std=CLC++.
This aligns with OpenCL C conversion and removes ambiguity
with OpenCL C++.
Differential Revision: https://reviews.llvm.org/D65102
llvm-svn: 367008
This adds a new vectorize predication loop hint:
#pragma clang loop vectorize_predicate(enable)
that can be used to indicate to the vectoriser that all (load/store)
instructions should be predicated (masked). This allows, for example, folding
of the remainder loop into the main loop.
This patch will be followed up with D64916 and D65197. The former is a
refactoring in the loopvectorizer and the groundwork to make tail loop folding
a more general concept, and in the latter the actual tail loop folding
transformation will be implemented.
Differential Revision: https://reviews.llvm.org/D64744
llvm-svn: 366989
Added documentation of C++ for OpenCL mode into Clang
User Manual and Language Extensions document.
Differential Revision: https://reviews.llvm.org/D64418
llvm-svn: 366351
Some targets such as Python 2.7.16 still use VERSION in
their builds. Without VERSION defined, the source code
has syntax errors.
Reverting as it will probably break many other things.
Noticed by Sterling Augustine
llvm-svn: 365992
Summary:
It has been introduced in 2011 for gcc compat:
ad1a4c6e89
it is probably time to remove it
Reviewers: rnk, dexonsmith
Reviewed By: rnk
Subscribers: dschuff, aheejin, fedor.sergeev, arphaman, cfe-commits
Tags: #clang
Differential Revision: https://reviews.llvm.org/D64062
llvm-svn: 365962
For background of BPF CO-RE project, please refer to
http://vger.kernel.org/bpfconf2019.html
In summary, BPF CO-RE intends to compile bpf programs
adjustable on struct/union layout change so the same
program can run on multiple kernels with adjustment
before loading based on native kernel structures.
In order to do this, we need keep track of GEP(getelementptr)
instruction base and result debuginfo types, so we
can adjust on the host based on kernel BTF info.
Capturing such information as an IR optimization is hard
as various optimization may have tweaked GEP and also
union is replaced by structure it is impossible to track
fieldindex for union member accesses.
Three intrinsic functions, preserve_{array,union,struct}_access_index,
are introducted.
addr = preserve_array_access_index(base, index, dimension)
addr = preserve_union_access_index(base, di_index)
addr = preserve_struct_access_index(base, gep_index, di_index)
here,
base: the base pointer for the array/union/struct access.
index: the last access index for array, the same for IR/DebugInfo layout.
dimension: the array dimension.
gep_index: the access index based on IR layout.
di_index: the access index based on user/debuginfo types.
If using these intrinsics blindly, i.e., transforming all GEPs
to these intrinsics and later on reducing them to GEPs, we have
seen up to 7% more instructions generated. To avoid such an overhead,
a clang builtin is proposed:
base = __builtin_preserve_access_index(base)
such that user wraps to-be-relocated GEPs in this builtin
and preserve_*_access_index intrinsics only apply to
those GEPs. Such a buyin will prevent performance degradation
if people do not use CO-RE, even for programs which use
bpf_probe_read().
For example, for the following example,
$ cat test.c
struct sk_buff {
int i;
int b1:1;
int b2:2;
union {
struct {
int o1;
int o2;
} o;
struct {
char flags;
char dev_id;
} dev;
int netid;
} u[10];
};
static int (*bpf_probe_read)(void *dst, int size, const void *unsafe_ptr)
= (void *) 4;
#define _(x) (__builtin_preserve_access_index(x))
int bpf_prog(struct sk_buff *ctx) {
char dev_id;
bpf_probe_read(&dev_id, sizeof(char), _(&ctx->u[5].dev.dev_id));
return dev_id;
}
$ clang -target bpf -O2 -g -emit-llvm -S -mllvm -print-before-all \
test.c >& log
The generated IR looks like below:
...
define dso_local i32 @bpf_prog(%struct.sk_buff*) #0 !dbg !15 {
%2 = alloca %struct.sk_buff*, align 8
%3 = alloca i8, align 1
store %struct.sk_buff* %0, %struct.sk_buff** %2, align 8, !tbaa !45
call void @llvm.dbg.declare(metadata %struct.sk_buff** %2, metadata !43, metadata !DIExpression()), !dbg !49
call void @llvm.lifetime.start.p0i8(i64 1, i8* %3) #4, !dbg !50
call void @llvm.dbg.declare(metadata i8* %3, metadata !44, metadata !DIExpression()), !dbg !51
%4 = load i32 (i8*, i32, i8*)*, i32 (i8*, i32, i8*)** @bpf_probe_read, align 8, !dbg !52, !tbaa !45
%5 = load %struct.sk_buff*, %struct.sk_buff** %2, align 8, !dbg !53, !tbaa !45
%6 = call [10 x %union.anon]* @llvm.preserve.struct.access.index.p0a10s_union.anons.p0s_struct.sk_buffs(
%struct.sk_buff* %5, i32 2, i32 3), !dbg !53, !llvm.preserve.access.index !19
%7 = call %union.anon* @llvm.preserve.array.access.index.p0s_union.anons.p0a10s_union.anons(
[10 x %union.anon]* %6, i32 1, i32 5), !dbg !53
%8 = call %union.anon* @llvm.preserve.union.access.index.p0s_union.anons.p0s_union.anons(
%union.anon* %7, i32 1), !dbg !53, !llvm.preserve.access.index !26
%9 = bitcast %union.anon* %8 to %struct.anon.0*, !dbg !53
%10 = call i8* @llvm.preserve.struct.access.index.p0i8.p0s_struct.anon.0s(
%struct.anon.0* %9, i32 1, i32 1), !dbg !53, !llvm.preserve.access.index !34
%11 = call i32 %4(i8* %3, i32 1, i8* %10), !dbg !52
%12 = load i8, i8* %3, align 1, !dbg !54, !tbaa !55
%13 = sext i8 %12 to i32, !dbg !54
call void @llvm.lifetime.end.p0i8(i64 1, i8* %3) #4, !dbg !56
ret i32 %13, !dbg !57
}
!19 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "sk_buff", file: !3, line: 1, size: 704, elements: !20)
!26 = distinct !DICompositeType(tag: DW_TAG_union_type, scope: !19, file: !3, line: 5, size: 64, elements: !27)
!34 = distinct !DICompositeType(tag: DW_TAG_structure_type, scope: !26, file: !3, line: 10, size: 16, elements: !35)
Note that @llvm.preserve.{struct,union}.access.index calls have metadata llvm.preserve.access.index
attached to instructions to provide struct/union debuginfo type information.
For &ctx->u[5].dev.dev_id,
. The "%6 = ..." represents struct member "u" with index 2 for IR layout and index 3 for DI layout.
. The "%7 = ..." represents array subscript "5".
. The "%8 = ..." represents union member "dev" with index 1 for DI layout.
. The "%10 = ..." represents struct member "dev_id" with index 1 for both IR and DI layout.
Basically, traversing the use-def chain recursively for the 3rd argument of bpf_probe_read() and
examining all preserve_*_access_index calls, the debuginfo struct/union/array access index
can be achieved.
The intrinsics also contain enough information to regenerate codes for IR layout.
For array and structure intrinsics, the proper GEP can be constructed.
For union intrinsics, replacing all uses of "addr" with "base" should be enough.
Signed-off-by: Yonghong Song <yhs@fb.com>
Differential Revision: https://reviews.llvm.org/D61809
llvm-svn: 365438
For background of BPF CO-RE project, please refer to
http://vger.kernel.org/bpfconf2019.html
In summary, BPF CO-RE intends to compile bpf programs
adjustable on struct/union layout change so the same
program can run on multiple kernels with adjustment
before loading based on native kernel structures.
In order to do this, we need keep track of GEP(getelementptr)
instruction base and result debuginfo types, so we
can adjust on the host based on kernel BTF info.
Capturing such information as an IR optimization is hard
as various optimization may have tweaked GEP and also
union is replaced by structure it is impossible to track
fieldindex for union member accesses.
Three intrinsic functions, preserve_{array,union,struct}_access_index,
are introducted.
addr = preserve_array_access_index(base, index, dimension)
addr = preserve_union_access_index(base, di_index)
addr = preserve_struct_access_index(base, gep_index, di_index)
here,
base: the base pointer for the array/union/struct access.
index: the last access index for array, the same for IR/DebugInfo layout.
dimension: the array dimension.
gep_index: the access index based on IR layout.
di_index: the access index based on user/debuginfo types.
If using these intrinsics blindly, i.e., transforming all GEPs
to these intrinsics and later on reducing them to GEPs, we have
seen up to 7% more instructions generated. To avoid such an overhead,
a clang builtin is proposed:
base = __builtin_preserve_access_index(base)
such that user wraps to-be-relocated GEPs in this builtin
and preserve_*_access_index intrinsics only apply to
those GEPs. Such a buyin will prevent performance degradation
if people do not use CO-RE, even for programs which use
bpf_probe_read().
For example, for the following example,
$ cat test.c
struct sk_buff {
int i;
int b1:1;
int b2:2;
union {
struct {
int o1;
int o2;
} o;
struct {
char flags;
char dev_id;
} dev;
int netid;
} u[10];
};
static int (*bpf_probe_read)(void *dst, int size, const void *unsafe_ptr)
= (void *) 4;
#define _(x) (__builtin_preserve_access_index(x))
int bpf_prog(struct sk_buff *ctx) {
char dev_id;
bpf_probe_read(&dev_id, sizeof(char), _(&ctx->u[5].dev.dev_id));
return dev_id;
}
$ clang -target bpf -O2 -g -emit-llvm -S -mllvm -print-before-all \
test.c >& log
The generated IR looks like below:
...
define dso_local i32 @bpf_prog(%struct.sk_buff*) #0 !dbg !15 {
%2 = alloca %struct.sk_buff*, align 8
%3 = alloca i8, align 1
store %struct.sk_buff* %0, %struct.sk_buff** %2, align 8, !tbaa !45
call void @llvm.dbg.declare(metadata %struct.sk_buff** %2, metadata !43, metadata !DIExpression()), !dbg !49
call void @llvm.lifetime.start.p0i8(i64 1, i8* %3) #4, !dbg !50
call void @llvm.dbg.declare(metadata i8* %3, metadata !44, metadata !DIExpression()), !dbg !51
%4 = load i32 (i8*, i32, i8*)*, i32 (i8*, i32, i8*)** @bpf_probe_read, align 8, !dbg !52, !tbaa !45
%5 = load %struct.sk_buff*, %struct.sk_buff** %2, align 8, !dbg !53, !tbaa !45
%6 = call [10 x %union.anon]* @llvm.preserve.struct.access.index.p0a10s_union.anons.p0s_struct.sk_buffs(
%struct.sk_buff* %5, i32 2, i32 3), !dbg !53, !llvm.preserve.access.index !19
%7 = call %union.anon* @llvm.preserve.array.access.index.p0s_union.anons.p0a10s_union.anons(
[10 x %union.anon]* %6, i32 1, i32 5), !dbg !53
%8 = call %union.anon* @llvm.preserve.union.access.index.p0s_union.anons.p0s_union.anons(
%union.anon* %7, i32 1), !dbg !53, !llvm.preserve.access.index !26
%9 = bitcast %union.anon* %8 to %struct.anon.0*, !dbg !53
%10 = call i8* @llvm.preserve.struct.access.index.p0i8.p0s_struct.anon.0s(
%struct.anon.0* %9, i32 1, i32 1), !dbg !53, !llvm.preserve.access.index !34
%11 = call i32 %4(i8* %3, i32 1, i8* %10), !dbg !52
%12 = load i8, i8* %3, align 1, !dbg !54, !tbaa !55
%13 = sext i8 %12 to i32, !dbg !54
call void @llvm.lifetime.end.p0i8(i64 1, i8* %3) #4, !dbg !56
ret i32 %13, !dbg !57
}
!19 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "sk_buff", file: !3, line: 1, size: 704, elements: !20)
!26 = distinct !DICompositeType(tag: DW_TAG_union_type, scope: !19, file: !3, line: 5, size: 64, elements: !27)
!34 = distinct !DICompositeType(tag: DW_TAG_structure_type, scope: !26, file: !3, line: 10, size: 16, elements: !35)
Note that @llvm.preserve.{struct,union}.access.index calls have metadata llvm.preserve.access.index
attached to instructions to provide struct/union debuginfo type information.
For &ctx->u[5].dev.dev_id,
. The "%6 = ..." represents struct member "u" with index 2 for IR layout and index 3 for DI layout.
. The "%7 = ..." represents array subscript "5".
. The "%8 = ..." represents union member "dev" with index 1 for DI layout.
. The "%10 = ..." represents struct member "dev_id" with index 1 for both IR and DI layout.
Basically, traversing the use-def chain recursively for the 3rd argument of bpf_probe_read() and
examining all preserve_*_access_index calls, the debuginfo struct/union/array access index
can be achieved.
The intrinsics also contain enough information to regenerate codes for IR layout.
For array and structure intrinsics, the proper GEP can be constructed.
For union intrinsics, replacing all uses of "addr" with "base" should be enough.
Signed-off-by: Yonghong Song <yhs@fb.com>
llvm-svn: 365435
Summary:
This patch implements the source location builtins `__builtin_LINE(), `__builtin_FUNCTION()`, `__builtin_FILE()` and `__builtin_COLUMN()`. These builtins are needed to implement [`std::experimental::source_location`](https://rawgit.com/cplusplus/fundamentals-ts/v2/main.html#reflection.src_loc.creation).
With the exception of `__builtin_COLUMN`, GCC also implements these builtins, and Clangs behavior is intended to match as closely as possible.
Reviewers: rsmith, joerg, aaron.ballman, bogner, majnemer, shafik, martong
Reviewed By: rsmith
Subscribers: rnkovacs, loskutov, riccibruno, mgorny, kunitoki, alexr, majnemer, hfinkel, cfe-commits
Differential Revision: https://reviews.llvm.org/D37035
llvm-svn: 360937
Summary:
This patch adds support for __builtin_dcbf for PPC.
__builtin_dcbf copies the contents of a modified block from the data cache
to main memory and flushes the copy from the data cache.
Differential revision: https://reviews.llvm.org/D59843
llvm-svn: 359517
Summary:
PowerPC64/PowerPC64le supports the builtin function __builtin_setrnd to set the floating point rounding mode. This function will use the least significant two bits of integer argument to set the floating point rounding mode.
double __builtin_setrnd(int mode);
The effective values for mode are:
0 - round to nearest
1 - round to zero
2 - round to +infinity
3 - round to -infinity
Note that the mode argument will modulo 4, so if the int argument is greater than 3, it will only use the least significant two bits of the mode. Namely, builtin_setrnd(102)) is equal to builtin_setrnd(2).
Reviewed By: jsji
Differential Revision: https://reviews.llvm.org/D59403
llvm-svn: 357242
This builtin has the same UI as __builtin_object_size, but has the
potential to be evaluated dynamically. It is meant to be used as a
drop-in replacement for libraries that use __builtin_object_size when
a dynamic checking mode is enabled. For instance,
__builtin_object_size fails to provide any extra checking in the
following function:
void f(size_t alloc) {
char* p = malloc(alloc);
strcpy(p, "foobar"); // expands to __builtin___strcpy_chk(p, "foobar", __builtin_object_size(p, 0))
}
This is an overflow if alloc < 7, but because LLVM can't fold the
object size intrinsic statically, it folds __builtin_object_size to
-1. With __builtin_dynamic_object_size, alloc is passed through to
__builtin___strcpy_chk.
rdar://32212419
Differential revision: https://reviews.llvm.org/D56760
llvm-svn: 352665
As Discussed here:
http://lists.llvm.org/pipermail/llvm-dev/2019-January/129543.html
There are problems exposing the _Float16 type on architectures that
haven't defined the ABI/ISel for the type yet, so we're temporarily
disabling the type and making it opt-in.
Differential Revision: https://reviews.llvm.org/D57188
Change-Id: I5db7366dedf1deb9485adb8948b1deb7e612a736
llvm-svn: 352221
Namespaces are introduced by adding an "identifier." before a
push/pop directive. Pop directives with namespaces can only pop a
attribute group that was pushed with the same namespace. Push and pop
directives that don't opt into namespaces have the same semantics.
This is necessary to prevent a pitfall of using multiple #pragma
clang attribute directives spread out in a large file, particularly
when macros are involved. It isn't easy to see which pop corripsonds
to which push, so its easy to inadvertently pop the wrong group.
Differential revision: https://reviews.llvm.org/D55628
llvm-svn: 349845
This clarifies that __has_cpp_attribute is no longer always an extension since it's now available in C++2a. Also, Both __has_cpp_attribute and __has_c_attribute can accept attribute scope tokens with alternative spelling (clang vs _Clang and gnu vs __gnu__).
llvm-svn: 347312
This reverts commit r345487, which reverted r345486. I think the crashes were
caused by an OOM on the builder, trying again to confirm...
llvm-svn: 345517
This commit enables pushing an empty #pragma clang attribute push, then adding
multiple attributes to it, then popping them all with #pragma clang attribute
pop, just like #pragma clang diagnostic. We still support the current way of
adding these, #pragma clang attribute push(__attribute__((...))), by treating it
like a combined push/attribute. This is needed to create macros like:
DO_SOMETHING_BEGIN(attr1, attr2, attr3)
// ...
DO_SOMETHING_END
rdar://45496947
Differential revision: https://reviews.llvm.org/D53621
llvm-svn: 345486
This is a partial retry of rL340137 (reverted at rL340138 because of gcc host compiler crashing)
with 1 change:
Remove the changes to make microsoft builtins also use the LLVM intrinsics.
This exposes the LLVM funnel shift intrinsics as more familiar bit rotation functions in clang
(when both halves of a funnel shift are the same value, it's a rotate).
We're free to name these as we want because we're not copying gcc, but if there's some other
existing art (eg, the microsoft ops) that we want to replicate, we can change the names.
The funnel shift intrinsics were added here:
https://reviews.llvm.org/D49242
With improved codegen in:
https://reviews.llvm.org/rL337966https://reviews.llvm.org/rL339359
And basic IR optimization added in:
https://reviews.llvm.org/rL338218https://reviews.llvm.org/rL340022
...so these are expected to produce asm output that's equal or better to the multi-instruction
alternatives using primitive C/IR ops.
In the motivating loop example from PR37387:
https://bugs.llvm.org/show_bug.cgi?id=37387#c7
...we get the expected 'rolq' x86 instructions if we substitute the rotate builtin into the source.
Differential Revision: https://reviews.llvm.org/D50924
llvm-svn: 340141
This is a retry of rL340135 (reverted at rL340136 because of gcc host compiler crashing)
with 2 changes:
1. Move the code into a helper to reduce code duplication (and hopefully work-around the crash).
2. The original commit had a formatting bug in the docs (missing an underscore).
Original commit message:
This exposes the LLVM funnel shift intrinsics as more familiar bit rotation functions in clang
(when both halves of a funnel shift are the same value, it's a rotate).
We're free to name these as we want because we're not copying gcc, but if there's some other
existing art (eg, the microsoft ops that are modified in this patch) that we want to replicate,
we can change the names.
The funnel shift intrinsics were added here:
https://reviews.llvm.org/D49242
With improved codegen in:
https://reviews.llvm.org/rL337966https://reviews.llvm.org/rL339359
And basic IR optimization added in:
https://reviews.llvm.org/rL338218https://reviews.llvm.org/rL340022
...so these are expected to produce asm output that's equal or better to the multi-instruction
alternatives using primitive C/IR ops.
In the motivating loop example from PR37387:
https://bugs.llvm.org/show_bug.cgi?id=37387#c7
...we get the expected 'rolq' x86 instructions if we substitute the rotate builtin into the source.
Differential Revision: https://reviews.llvm.org/D50924
llvm-svn: 340137
This exposes the LLVM funnel shift intrinsics as more familiar bit rotation functions in clang
(when both halves of a funnel shift are the same value, it's a rotate).
We're free to name these as we want because we're not copying gcc, but if there's some other
existing art (eg, the microsoft ops that are modified in this patch) that we want to replicate,
we can change the names.
The funnel shift intrinsics were added here:
D49242
With improved codegen in:
rL337966
rL339359
And basic IR optimization added in:
rL338218
rL340022
...so these are expected to produce asm output that's equal or better to the multi-instruction
alternatives using primitive C/IR ops.
In the motivating loop example from PR37387:
https://bugs.llvm.org/show_bug.cgi?id=37387#c7
...we get the expected 'rolq' x86 instructions if we substitute the rotate builtin into the source.
Differential Revision: https://reviews.llvm.org/D50924
llvm-svn: 340135
These intrinsics work exactly as all other atomic_fetch_* intrinsics and allow to create *atomicrmw* with ordering.
Updated the clang-extensions document.
Differential Revision: https://reviews.llvm.org/D46386
llvm-svn: 332193
ARC mode.
Declaring __strong pointer fields in structs was not allowed in
Objective-C ARC until now because that would make the struct non-trivial
to default-initialize, copy/move, and destroy, which is not something C
was designed to do. This patch lifts that restriction.
Special functions for non-trivial C structs are synthesized that are
needed to default-initialize, copy/move, and destroy the structs and
manage the ownership of the objects the __strong pointer fields point
to. Non-trivial structs passed to functions are destructed in the callee
function.
rdar://problem/33599681
Differential Revision: https://reviews.llvm.org/D41228
llvm-svn: 326307
This adds the frontend support required to support the use of the
comment pragma to enable auto linking on ELFish targets. This is a
generic ELF extension supported by LLVM. We need to change the handling
for the "dependentlib" in order to accommodate the previously discussed
encoding for the dependent library descriptor. Without the custom
handling of the PCK_Lib directive, the -l prefixed option would be
encoded into the resulting object (which is treated as a frontend
error).
llvm-svn: 324438
Summary:
The STL types `std::pair` and `std::tuple` can both store reference types. However their constructors cannot adequately check if the initialization of reference types is safe. For example:
```
std::tuple<std::tuple<int> const&> t = 42;
// The stored reference is already dangling.
```
Libc++ has a best effort attempts in tuple to diagnose this, but they're not able to handle all valid cases (If I'm not mistaken). For example initialization of a reference from the result of a class's conversion operator. Libc++ would benefit from having a builtin traits which can provide a much better implementation.
This patch introduce the `__reference_binds_to_temporary(T, U)` trait that determines whether a reference of type `T` bound to an expression of type `U` would bind to a materialized temporary object.
Note that the trait simply returns false if `T` is not a reference type instead of reporting it as an error.
```
static_assert(__is_constructible(int const&, long));
static_assert(__reference_binds_to_temporary(int const&, long));
```
Reviewers: majnemer, rsmith
Reviewed By: rsmith
Subscribers: compnerd, cfe-commits
Differential Revision: https://reviews.llvm.org/D29930
llvm-svn: 322334
This behaves similar to the __has_cpp_attribute builtin macro in that it allows users to detect whether an attribute is supported with the [[]] spelling syntax, which can be enabled in C with -fdouble-square-bracket-attributes.
llvm-svn: 320088
This documents the differences/interactions between _Float16 and __fp16
and is a companion change for the _Float16 type implementation (r312794).
Differential Revision: https://reviews.llvm.org/D35295
llvm-svn: 317558
OpenCL 2.0 atomic builtin functions have a scope argument which is ideally
represented as synchronization scope argument in LLVM atomic instructions.
Clang supports translating Clang atomic builtin functions to LLVM atomic
instructions. However it currently does not support synchronization scope
of LLVM atomic instructions. Without this, users have to use LLVM assembly
code to implement OpenCL atomic builtin functions.
This patch adds OpenCL 2.0 atomic builtin functions as Clang builtin
functions, which supports generating LLVM atomic instructions with
synchronization scope operand.
Currently only constant memory scope argument is supported. Support of
non-constant memory scope argument will be added later.
Differential Revision: https://reviews.llvm.org/D28691
llvm-svn: 310082
This patch provides a means to specify section-names for global variables,
functions and static variables, using #pragma directives.
This feature is only defined to work sensibly for ELF targets.
One can specify section names as:
#pragma clang section bss="myBSS" data="myData" rodata="myRodata" text="myText"
One can "unspecify" a section name with empty string e.g.
#pragma clang section bss="" data="" text="" rodata=""
Reviewers: Roger Ferrer, Jonathan Roelofs, Reid Kleckner
Differential Revision: https://reviews.llvm.org/D33412
llvm-svn: 304705
Anastasia Stulova