[clang] cee5b87 - [Clang] Fix linker error for function multiversioning (#71706)
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cfe-commits at lists.llvm.org
Tue Dec 5 15:11:57 PST 2023
Author: elizabethandrews
Date: 2023-12-05T18:11:53-05:00
New Revision: cee5b8777fa98312b05bf8aa81554910a8f867c5
URL: https://github.com/llvm/llvm-project/commit/cee5b8777fa98312b05bf8aa81554910a8f867c5
DIFF: https://github.com/llvm/llvm-project/commit/cee5b8777fa98312b05bf8aa81554910a8f867c5.diff
LOG: [Clang] Fix linker error for function multiversioning (#71706)
Currently target_clones attribute results in a linker error when there
are no multi-versioned function declarations in the calling TU.
In the calling TU, the call is generated with the ‘normal’ assembly
name. This does not match any of the versions or the ifunc, since
version mangling includes a .versionstring, and the ifunc includes
.ifunc suffix. The linker error is not seen with GCC since the mangling
for the ifunc symbol in GCC is the ‘normal’ assembly name for function
i.e. no ifunc suffix.
This PR removes the .ifunc suffix to match GCC. It also adds alias with
the .ifunc suffix so as to ensure backward compatibility.
The changes exclude aarch64 target because the mangling for default
versions on aarch64 does not include a .default suffix and is the
'normal' assembly name, unlike other targets. It is not clear to me what
the correct behavior for this target is.
Old Phabricator review - https://reviews.llvm.org/D158666
---------
Co-authored-by: Tom Honermann <tom at honermann.net>
Added:
Modified:
clang/docs/ReleaseNotes.rst
clang/include/clang/Basic/AttrDocs.td
clang/lib/CodeGen/CodeGenModule.cpp
clang/test/CodeGen/attr-target-clones.c
clang/test/CodeGenCXX/attr-target-clones.cpp
Removed:
################################################################################
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 828dd10e3d6db..89ea2f0930cec 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -651,6 +651,9 @@ Bug Fixes in This Version
- Fixed false positive error emitted by clang when performing qualified name
lookup and the current class instantiation has dependent bases.
Fixes (`#13826 <https://github.com/llvm/llvm-project/issues/13826>`_)
+- Fix the name of the ifunc symbol emitted for multiversion functions declared with the
+ ``target_clones`` attribute. This addresses a linker error that would otherwise occur
+ when these functions are referenced from other TUs.
- Fixes compile error that double colon operator cannot resolve macro with parentheses.
Fixes (`#64467 <https://github.com/llvm/llvm-project/issues/64467>`_)
- Clang's ``-Wchar-subscripts`` no longer warns on chars whose values are known non-negative constants.
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index 53c3dff19fc9b..bbe4de94cbabe 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -2552,6 +2552,13 @@ example, the following will emit 4 versions of the function:
__attribute__((target_clones("arch=atom,avx2","arch=ivybridge","default")))
void foo() {}
+For targets that support the GNU indirect function (IFUNC) feature, dispatch
+is performed by emitting an indirect function that is resolved to the appropriate
+target clone at load time. The indirect function is given the name the
+multiversioned function would have if it had been declared without the attribute.
+For backward compatibility with earlier Clang releases, a function alias with an
+``.ifunc`` suffix is also emitted. The ``.ifunc`` suffixed symbol is a deprecated
+feature and support for it may be removed in the future.
}];
}
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index dea58a7ff4146..6a20723bf2bca 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -4178,8 +4178,29 @@ void CodeGenModule::emitMultiVersionFunctions() {
}
llvm::Constant *ResolverConstant = GetOrCreateMultiVersionResolver(GD);
- if (auto *IFunc = dyn_cast<llvm::GlobalIFunc>(ResolverConstant))
+ if (auto *IFunc = dyn_cast<llvm::GlobalIFunc>(ResolverConstant)) {
ResolverConstant = IFunc->getResolver();
+ // In Aarch64, default versions of multiversioned functions are mangled to
+ // their 'normal' assembly name. This deviates from other targets which
+ // append a '.default' string. As a result we need to continue appending
+ // .ifunc in Aarch64.
+ // FIXME: Should Aarch64 mangling for 'default' multiversion function and
+ // in turn ifunc function match that of other targets?
+ if (FD->isTargetClonesMultiVersion() &&
+ !getTarget().getTriple().isAArch64()) {
+ const CGFunctionInfo &FI = getTypes().arrangeGlobalDeclaration(GD);
+ llvm::FunctionType *DeclTy = getTypes().GetFunctionType(FI);
+ std::string MangledName = getMangledNameImpl(
+ *this, GD, FD, /*OmitMultiVersionMangling=*/true);
+ // In prior versions of Clang, the mangling for ifuncs incorrectly
+ // included an .ifunc suffix. This alias is generated for backward
+ // compatibility. It is deprecated, and may be removed in the future.
+ auto *Alias = llvm::GlobalAlias::create(
+ DeclTy, 0, getMultiversionLinkage(*this, GD),
+ MangledName + ".ifunc", IFunc, &getModule());
+ SetCommonAttributes(FD, Alias);
+ }
+ }
llvm::Function *ResolverFunc = cast<llvm::Function>(ResolverConstant);
ResolverFunc->setLinkage(getMultiversionLinkage(*this, GD));
@@ -4346,10 +4367,19 @@ llvm::Constant *CodeGenModule::GetOrCreateMultiVersionResolver(GlobalDecl GD) {
// Holds the name of the resolver, in ifunc mode this is the ifunc (which has
// a separate resolver).
std::string ResolverName = MangledName;
- if (getTarget().supportsIFunc())
- ResolverName += ".ifunc";
- else if (FD->isTargetMultiVersion())
+ if (getTarget().supportsIFunc()) {
+ // In Aarch64, default versions of multiversioned functions are mangled to
+ // their 'normal' assembly name. This deviates from other targets which
+ // append a '.default' string. As a result we need to continue appending
+ // .ifunc in Aarch64.
+ // FIXME: Should Aarch64 mangling for 'default' multiversion function and
+ // in turn ifunc function match that of other targets?
+ if (!FD->isTargetClonesMultiVersion() ||
+ getTarget().getTriple().isAArch64())
+ ResolverName += ".ifunc";
+ } else if (FD->isTargetMultiVersion()) {
ResolverName += ".resolver";
+ }
// If the resolver has already been created, just return it.
if (llvm::GlobalValue *ResolverGV = GetGlobalValue(ResolverName))
diff --git a/clang/test/CodeGen/attr-target-clones.c b/clang/test/CodeGen/attr-target-clones.c
index 98ffea40f56d8..4b99914031b10 100644
--- a/clang/test/CodeGen/attr-target-clones.c
+++ b/clang/test/CodeGen/attr-target-clones.c
@@ -16,13 +16,23 @@
// LINUX: @__cpu_model = external dso_local global { i32, i32, i32, [1 x i32] }
// LINUX: @__cpu_features2 = external dso_local global [3 x i32]
-// LINUX: @internal.ifunc = internal ifunc i32 (), ptr @internal.resolver
-// LINUX: @foo.ifunc = weak_odr ifunc i32 (), ptr @foo.resolver
-// LINUX: @foo_dupes.ifunc = weak_odr ifunc void (), ptr @foo_dupes.resolver
-// LINUX: @unused.ifunc = weak_odr ifunc void (), ptr @unused.resolver
-// LINUX: @foo_inline.ifunc = weak_odr ifunc i32 (), ptr @foo_inline.resolver
-// LINUX: @foo_inline2.ifunc = weak_odr ifunc i32 (), ptr @foo_inline2.resolver
-// LINUX: @foo_used_no_defn.ifunc = weak_odr ifunc i32 (), ptr @foo_used_no_defn.resolver
+// LINUX: @internal.ifunc = internal alias i32 (), ptr @internal
+// LINUX: @foo.ifunc = weak_odr alias i32 (), ptr @foo
+// LINUX: @foo_dupes.ifunc = weak_odr alias void (), ptr @foo_dupes
+// LINUX: @unused.ifunc = weak_odr alias void (), ptr @unused
+// LINUX: @foo_inline.ifunc = weak_odr alias i32 (), ptr @foo_inline
+// LINUX: @foo_inline2.ifunc = weak_odr alias i32 (), ptr @foo_inline2
+// LINUX: @foo_used_no_defn.ifunc = weak_odr alias i32 (), ptr @foo_used_no_defn
+// LINUX: @isa_level.ifunc = weak_odr alias i32 (i32), ptr @isa_level
+
+// LINUX: @internal = internal ifunc i32 (), ptr @internal.resolver
+// LINUX: @foo = weak_odr ifunc i32 (), ptr @foo.resolver
+// LINUX: @foo_dupes = weak_odr ifunc void (), ptr @foo_dupes.resolver
+// LINUX: @unused = weak_odr ifunc void (), ptr @unused.resolver
+// LINUX: @foo_inline = weak_odr ifunc i32 (), ptr @foo_inline.resolver
+// LINUX: @foo_inline2 = weak_odr ifunc i32 (), ptr @foo_inline2.resolver
+// LINUX: @foo_used_no_defn = weak_odr ifunc i32 (), ptr @foo_used_no_defn.resolver
+// LINUX: @isa_level = weak_odr ifunc i32 (i32), ptr @isa_level.resolver
static int __attribute__((target_clones("sse4.2, default"))) internal(void) { return 0; }
int use(void) { return internal(); }
@@ -60,7 +70,7 @@ void bar2(void) {
// LINUX: define {{.*}}void @bar2()
// WINDOWS: define dso_local void @bar2()
foo_dupes();
- // LINUX: call void @foo_dupes.ifunc()
+ // LINUX: call void @foo_dupes()
// WINDOWS: call void @foo_dupes()
}
@@ -68,7 +78,7 @@ int bar(void) {
// LINUX: define {{.*}}i32 @bar() #[[DEF:[0-9]+]]
// WINDOWS: define dso_local i32 @bar() #[[DEF:[0-9]+]]
return foo();
- // LINUX: call i32 @foo.ifunc()
+ // LINUX: call i32 @foo()
// WINDOWS: call i32 @foo()
}
@@ -95,8 +105,8 @@ int bar3(void) {
// LINUX: define {{.*}}i32 @bar3()
// WINDOWS: define dso_local i32 @bar3()
return foo_inline() + foo_inline2();
- // LINUX: call i32 @foo_inline.ifunc()
- // LINUX: call i32 @foo_inline2.ifunc()
+ // LINUX: call i32 @foo_inline()
+ // LINUX: call i32 @foo_inline2()
// WINDOWS: call i32 @foo_inline()
// WINDOWS: call i32 @foo_inline2()
}
@@ -134,7 +144,7 @@ int test_foo_used_no_defn(void) {
// LINUX: define {{.*}}i32 @test_foo_used_no_defn()
// WINDOWS: define dso_local i32 @test_foo_used_no_defn()
return foo_used_no_defn();
- // LINUX: call i32 @foo_used_no_defn.ifunc()
+ // LINUX: call i32 @foo_used_no_defn()
// WINDOWS: call i32 @foo_used_no_defn()
}
diff --git a/clang/test/CodeGenCXX/attr-target-clones.cpp b/clang/test/CodeGenCXX/attr-target-clones.cpp
index 86293b98dbbd3..fd2d38062a71e 100644
--- a/clang/test/CodeGenCXX/attr-target-clones.cpp
+++ b/clang/test/CodeGenCXX/attr-target-clones.cpp
@@ -1,13 +1,20 @@
// RUN: %clang_cc1 -std=c++11 -triple x86_64-linux-gnu -emit-llvm %s -o - | FileCheck %s --check-prefix=LINUX
// RUN: %clang_cc1 -std=c++11 -triple x86_64-windows-pc -emit-llvm %s -o - | FileCheck %s --check-prefix=WINDOWS
+// Aliases for ifuncs
+// LINUX: @_Z10overloadedi.ifunc = weak_odr alias i32 (i32), ptr @_Z10overloadedi
+// LINUX: @_Z10overloadedPKc.ifunc = weak_odr alias i32 (ptr), ptr @_Z10overloadedPKc
+// LINUX: @_ZN1CIssE3fooEv.ifunc = weak_odr alias i32 (ptr), ptr @_ZN1CIssE3fooEv
+// LINUX: @_ZN1CIisE3fooEv.ifunc = weak_odr alias i32 (ptr), ptr @_ZN1CIisE3fooEv
+// LINUX: @_ZN1CIdfE3fooEv.ifunc = weak_odr alias i32 (ptr), ptr @_ZN1CIdfE3fooEv
+
// Overloaded ifuncs
-// LINUX: @_Z10overloadedi.ifunc = weak_odr ifunc i32 (i32), ptr @_Z10overloadedi.resolver
-// LINUX: @_Z10overloadedPKc.ifunc = weak_odr ifunc i32 (ptr), ptr @_Z10overloadedPKc.resolver
+// LINUX: @_Z10overloadedi = weak_odr ifunc i32 (i32), ptr @_Z10overloadedi.resolver
+// LINUX: @_Z10overloadedPKc = weak_odr ifunc i32 (ptr), ptr @_Z10overloadedPKc.resolver
// struct 'C' ifuncs, note the 'float, U' one doesn't get one.
-// LINUX: @_ZN1CIssE3fooEv.ifunc = weak_odr ifunc i32 (ptr), ptr @_ZN1CIssE3fooEv.resolver
-// LINUX: @_ZN1CIisE3fooEv.ifunc = weak_odr ifunc i32 (ptr), ptr @_ZN1CIisE3fooEv.resolver
-// LINUX: @_ZN1CIdfE3fooEv.ifunc = weak_odr ifunc i32 (ptr), ptr @_ZN1CIdfE3fooEv.resolver
+// LINUX: @_ZN1CIssE3fooEv = weak_odr ifunc i32 (ptr), ptr @_ZN1CIssE3fooEv.resolver
+// LINUX: @_ZN1CIisE3fooEv = weak_odr ifunc i32 (ptr), ptr @_ZN1CIisE3fooEv.resolver
+// LINUX: @_ZN1CIdfE3fooEv = weak_odr ifunc i32 (ptr), ptr @_ZN1CIdfE3fooEv.resolver
int __attribute__((target_clones("sse4.2", "default"))) overloaded(int) { return 1; }
// LINUX: define {{.*}}i32 @_Z10overloadedi.sse4.2.0(i32{{.+}})
@@ -37,10 +44,10 @@ int __attribute__((target_clones("arch=ivybridge", "default"))) overloaded(const
void use_overloaded() {
overloaded(1);
- // LINUX: call noundef i32 @_Z10overloadedi.ifunc
+ // LINUX: call noundef i32 @_Z10overloadedi
// WINDOWS: call noundef i32 @"?overloaded@@YAHH at Z"
overloaded(nullptr);
- // LINUX: call noundef i32 @_Z10overloadedPKc.ifunc
+ // LINUX: call noundef i32 @_Z10overloadedPKc
// WINDOWS: call noundef i32 @"?overloaded@@YAHPEBD at Z"
}
@@ -64,11 +71,11 @@ int __attribute__((target_clones("sse4.2", "default"))) foo(){ return 3;}
void uses_specialized() {
C<short, short> c;
c.foo();
- // LINUX: call noundef i32 @_ZN1CIssE3fooEv.ifunc(ptr
+ // LINUX: call noundef i32 @_ZN1CIssE3fooEv(ptr
// WINDOWS: call noundef i32 @"?foo@?$C at FF@@QEAAHXZ"(ptr
C<int, short> c2;
c2.foo();
- // LINUX: call noundef i32 @_ZN1CIisE3fooEv.ifunc(ptr
+ // LINUX: call noundef i32 @_ZN1CIisE3fooEv(ptr
// WINDOWS: call noundef i32 @"?foo@?$C at HF@@QEAAHXZ"(ptr
C<float, short> c3;
c3.foo();
@@ -77,7 +84,7 @@ void uses_specialized() {
// WINDOWS: call noundef i32 @"?foo@?$C at MF@@QEAAHXZ"(ptr
C<double, float> c4;
c4.foo();
- // LINUX: call noundef i32 @_ZN1CIdfE3fooEv.ifunc(ptr
+ // LINUX: call noundef i32 @_ZN1CIdfE3fooEv(ptr
// WINDOWS: call noundef i32 @"?foo@?$C at NM@@QEAAHXZ"(ptr
}
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