Currently we need at least one more version other than the default to
trigger FMV. However we would like a header file declaration
__attribute__((target_version("default"))) void f(void);
to guarantee that there will be f.default
We have a dedicated test to check the target-features for FMV
(clang/test/CodeGen/aarch64-fmv-dependencies.c) therefore I am removing
the autogenerated checks from irrelevant tests since the noise is making
it harder to review actual codegen changes.
It was raised in https://github.com/llvm/llvm-project/issues/81494 that
we are not generating correct code when there is no TU-local caller.
The suggestion was to emit a resolver:
* Whenever there is a use in the TU.
* When the TU has a definition of the default version.
See the comment for more details:
https://github.com/llvm/llvm-project/issues/81494#issuecomment-1985963497
This got addressed with https://github.com/llvm/llvm-project/pull/84405.
Generating a resolver on use means that we may end up with multiple
resolvers across different translation units. Those resolvers may not be
the same because each translation unit may contain different version
declarations (user's fault). Therefore the order of linking the final
image determines which of these weak symbols gets selected, resulting in
non consisted behavior. I am proposing to stop emitting a resolver on
use and only do so in the translation unit which contains the default
definition. This way we guarantee the existence of a single resolver.
Now, when a versioned function is used we want to emit a declaration of
the function symbol omitting the multiversion mangling.
I have added a requirement to ACLE mandating that all the function
versions are declared in the translation unit which contains the default
definition: https://github.com/ARM-software/acle/pull/328
Fixes a crash and cleans up some dead code.
namespace Foo {
int bar();
__attribute((target_version("default"))) int bar() { return 0; }
__attribute((target_version("mops"))) int bar() { return 1; }
}
$ clang++ --target=aarch64-linux-gnu --rtlib=compiler-rt fmv.cpp
None multiversion type isn't valid here
UNREACHABLE executed at clang/lib/CodeGen/CodeGenModule.cpp:1840! ...
getMangledNameImpl
clang::CodeGen::CodeGenModule::getMangledName
clang::CodeGen::CodeGenModule::EmitGlobal
Long story short the interaction of two optimizations happening in
GlobalOpt results in a crash. For more details look at the issue
https://github.com/llvm/llvm-project/issues/96197. I will be fixing this
in GlobalOpt but it is a conservative solution since it won't allow us
to optimize resolvers which return a pointer to a function whose
definition is in another TU when compiling without LTO:
```
__attribute__((target_version("simd"))) void bar(void);
__attribute__((target_version("default"))) void bar(void);
int foo() { bar(); }
```
fixes: #96197
Fixes the following bug:
namespace Name {
int __attribute((target_version("default"))) foo() { return 0; }
}
namespace Name {
int __attribute((target_version("sve"))) foo() { return 1; }
}
int bar() { return Name::foo(); }
error: redefinition of 'foo'
int __attribute((target_version("sve"))) foo() { return 1; }
note: previous definition is here
int __attribute((target_version("default"))) foo() { return 0; }
While fixing this I also found that in the absence of default version
declaration, the one we implicitly create has incorrect mangling if
we are in a namespace:
namespace OtherName {
int __attribute((target_version("sve"))) foo() { return 2; }
}
int baz() { return OtherName::foo(); }
In this example instead of creating a declaration for the symbol
@_ZN9OtherName3fooEv.default we are creating one for the symbol
@_Z3foov.default (the namespace mangling prefix is omitted).
This has now been fixed.
