This adds infrastructure for a multiversioning whitelist, plus adds
'used' to the allowed list with 'target'. The behavior here mirrors the
implementation in GCC, where 'used' only applies to the single
declaration and doesn't apply to the ifunc or resolver.
This is not being applied to cpu_dispatch and cpu_specific, since the
rules are more complicated for cpu_specific, which emits multiple
symbols. Additionally, the author isn't currently aware of uses in the
wild of this combination, but is aware of a number of target+used
combinations.
The initial implementation only did 'first declaration renaming' when
a default version came after. This is insufficient in cases where a
default does not exist, so this patch makes sure that we do the renaming
in all cases.
This renaming is necessary because we emit the first declaration before
knowing that it IS a target multiversion function, which would change
its name. The second declaration (the one that caused the
multiversioning) then needs to make sure that the first one has its name
changed to be consistent with the resolver usage.
Summary:
Clang -fpic defaults to -fno-semantic-interposition (GCC -fpic defaults
to -fsemantic-interposition).
Users need to specify -fsemantic-interposition to get semantic
interposition behavior.
Semantic interposition is currently a best-effort feature. There may
still be some cases where it is not handled well.
Reviewers: peter.smith, rnk, serge-sans-paille, sfertile, jfb, jdoerfert
Subscribers: dschuff, jyknight, dylanmckay, nemanjai, jvesely, kbarton, fedor.sergeev, asb, rbar, johnrusso, simoncook, sabuasal, niosHD, jrtc27, zzheng, edward-jones, atanasyan, rogfer01, MartinMosbeck, brucehoult, the_o, arphaman, PkmX, jocewei, jsji, Jim, lenary, s.egerton, pzheng, sameer.abuasal, apazos, luismarques, cfe-commits
Tags: #clang
Differential Revision: https://reviews.llvm.org/D73865
Multi-versioned functions defined by cpu_dispatch and implemented with IFunc
can not be called outside the translation units where they are defined due to
lack of symbols. This patch add function aliases for these functions and thus
make them visible outside.
Differential Revision: https://reviews.llvm.org/D67058
Patch by Senran Zhang
llvm-svn: 371586
For consistency with normal instructions and clarity when reading IR,
it's best to print the %0, %1, ... names of function arguments in
definitions.
Also modifies the parser to accept IR in that form for obvious reasons.
llvm-svn: 367755
Inline cpu_specific versions referenced before the cpu_dispatch function
weren't properly emitted, since they hadn't been referred to. This
patch ensures that during resolver generation that all appropriate
versions are emitted.
Change-Id: I94c3766aaf9c75ca07a0ad8258efdbb834654ff8
llvm-svn: 348600
This reverts commit 65df29f9318ac13a633c0ce13b2b0bccf06e79ca.
AS suggested by @rsmith here: https://reviews.llvm.org/rL345839
I'm reverting this and solving the initial problem in a different way.
llvm-svn: 348595
Declarations without the attribute were disallowed because it would be
ambiguous which 'target' it was supposed to be on. For example:
void ___attribute__((target("v1"))) foo();
void foo(); // Redecl of above, or fwd decl of below?
void ___attribute__((target("v2"))) foo();
However, a first declaration doesn't have that problem, and erroring
prevents it from working in cases where the forward declaration is
useful.
Additionally, a forward declaration of target==default wouldn't properly
cause multiversioning, so this patch fixes that.
The patch was not split since the 'default' fix would require
implementing the same check for that case, followed by undoing the same
change for the fwd-decl implementation.
Change-Id: I66f2c5bc2477bcd3f7544b9c16c83ece257077b0
llvm-svn: 347805
Multiverson function versions are always used (by the resolver), so ensure that
they are always emitted.
Change-Id: I5d2e0841fddf0d18918b3fb92ae76814add7ee96
llvm-svn: 345839
Similar to how ICC handles CPU-Dispatch on Windows, this patch uses the
resolver function directly to forward the call to the proper function.
This is not nearly as efficient as IFuncs of course, but is still quite
useful for large functions specifically developed for certain
processors.
This is unfortunately still limited to x86, since it depends on
__builtin_cpu_supports and __builtin_cpu_is, which are x86 builtins.
The naming for the resolver/forwarding function for cpu-dispatch was
taken from ICC's implementation, which uses the unmodified name for this
(no mangling additions). This is possible, since cpu-dispatch uses '.A'
for the 'default' version.
In 'target' multiversioning, this function keeps the '.resolver'
extension in order to keep the default function keeping the default
mangling.
Change-Id: I4731555a39be26c7ad59a2d8fda6fa1a50f73284
Differential Revision: https://reviews.llvm.org/D53586
llvm-svn: 345298
Since multiversion variant functions can be inline, in C they become
available-externally linkage. This ends up causing the variants to not
be emitted, and not available to the linker.
The solution is to make sure that multiversion functions are always
emitted by marking them linkonce.
Change-Id: I897aa37c7cbba0c1eb2c57ee881d5000a2113b75
llvm-svn: 344957
Summary:
The multiversioning code repurposed the code from __builtin_cpu_supports for checking if a single feature is enabled. That code essentially performed (_cpu_features & (1 << C)) != 0. But with the multiversioning path, the mask is no longer guaranteed to be a power of 2. So we return true anytime any one of the bits in the mask is set not just all of the bits.
The correct check is (_cpu_features & mask) == mask
Reviewers: erichkeane, echristo
Reviewed By: echristo
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D53460
llvm-svn: 344824
GCC's attribute 'target', in addition to being an optimization hint,
also allows function multiversioning. We currently have the former
implemented, this is the latter's implementation.
This works by enabling functions with the same name/signature to coexist,
so that they can all be emitted. Multiversion state is stored in the
FunctionDecl itself, and SemaDecl manages the definitions.
Note that it ends up having to permit redefinition of functions so
that they can all be emitted. Additionally, all versions of the function
must be emitted, so this also manages that.
Note that this includes some additional rules that GCC does not, since
defining something as a MultiVersion function after a usage has been made illegal.
The only 'history rewriting' that happens is if a function is emitted before
it has been converted to a multiversion'ed function, at which point its name
needs to be changed.
Function templates and virtual functions are NOT yet supported (not supported
in GCC either).
Additionally, constructors/destructors are disallowed, but the former is
planned.
llvm-svn: 322028
Craig Topper