probinson created this revision.
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People use -ffunction-sections to put each function into its own
object-file section; this makes linker garbage-collection simpler.
However, if there's an explicit __attribute__((section("name"))
on the function, all functions with that attribute end up in a
single section, defeating the linker GC.
Use section groups to make these things work together.
https://reviews.llvm.org/D143745
Files:
clang/lib/CodeGen/CodeGenModule.cpp
clang/test/CodeGen/section-attr-comdat.cpp
Index: clang/test/CodeGen/section-attr-comdat.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGen/section-attr-comdat.cpp
@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -triple=x86_64-linux -emit-llvm %s -o - | \
+// RUN: FileCheck %s --check-prefix=NOCOMDAT
+// RUN: %clang_cc1 -triple=x86_64-linux -emit-llvm -ffunction-sections %s -o -
| \
+// RUN: FileCheck %s --check-prefix=COMDAT
+
+// template function = comdat always.
+template<typename T>
+__attribute__((section("foo"))) T ftemplate(T a) { return a + 1; }
+__attribute__((section("foo"))) int fglobal(int a) { return ftemplate(a) + 2; }
+
+// NOCOMDAT-DAG: ${{.*}}ftemplate{{.*}} = comdat any
+// NOCOMDAT-DAG: define {{.*}}ftemplate{{.*}} section "foo" comdat {
+// NOCOMDAT-DAG: define {{.*}}fglobal{{.*}} section "foo" {
+
+// COMDAT-DAG: ${{.*}}ftemplate{{.*}} = comdat any
+// COMDAT-DAG: ${{.*}}fglobal{{.*}} = comdat nodeduplicate
+// COMDAT-DAG: define {{.*}}ftemplate{{.*}} section "foo" comdat {
+// COMDAT-DAG: define {{.*}}fglobal{{.*}} section "foo" comdat {
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -2293,6 +2293,18 @@
if (auto *SA = D->getAttr<PragmaClangTextSectionAttr>())
if (!D->getAttr<SectionAttr>())
F->addFnAttr("implicit-section-name", SA->getName());
+ // If we have -ffunction-sections, and also an explicit section name,
+ // put the function into a section group so that various linker GC
+ // operations will still work with this function.
+ if (CodeGenOpts.FunctionSections && getTriple().supportsCOMDAT() &&
+ D->hasAttr<SectionAttr>()) {
+ // Don't replace a real comdat.
+ if (!F->getComdat()) {
+ llvm::Comdat *C = TheModule.getOrInsertComdat(F->getName());
+ C->setSelectionKind(llvm::Comdat::NoDeduplicate);
+ F->setComdat(C);
+ }
+ }
llvm::AttrBuilder Attrs(F->getContext());
if (GetCPUAndFeaturesAttributes(GD, Attrs)) {
Index: clang/test/CodeGen/section-attr-comdat.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGen/section-attr-comdat.cpp
@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -triple=x86_64-linux -emit-llvm %s -o - | \
+// RUN: FileCheck %s --check-prefix=NOCOMDAT
+// RUN: %clang_cc1 -triple=x86_64-linux -emit-llvm -ffunction-sections %s -o - | \
+// RUN: FileCheck %s --check-prefix=COMDAT
+
+// template function = comdat always.
+template<typename T>
+__attribute__((section("foo"))) T ftemplate(T a) { return a + 1; }
+__attribute__((section("foo"))) int fglobal(int a) { return ftemplate(a) + 2; }
+
+// NOCOMDAT-DAG: ${{.*}}ftemplate{{.*}} = comdat any
+// NOCOMDAT-DAG: define {{.*}}ftemplate{{.*}} section "foo" comdat {
+// NOCOMDAT-DAG: define {{.*}}fglobal{{.*}} section "foo" {
+
+// COMDAT-DAG: ${{.*}}ftemplate{{.*}} = comdat any
+// COMDAT-DAG: ${{.*}}fglobal{{.*}} = comdat nodeduplicate
+// COMDAT-DAG: define {{.*}}ftemplate{{.*}} section "foo" comdat {
+// COMDAT-DAG: define {{.*}}fglobal{{.*}} section "foo" comdat {
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -2293,6 +2293,18 @@
if (auto *SA = D->getAttr<PragmaClangTextSectionAttr>())
if (!D->getAttr<SectionAttr>())
F->addFnAttr("implicit-section-name", SA->getName());
+ // If we have -ffunction-sections, and also an explicit section name,
+ // put the function into a section group so that various linker GC
+ // operations will still work with this function.
+ if (CodeGenOpts.FunctionSections && getTriple().supportsCOMDAT() &&
+ D->hasAttr<SectionAttr>()) {
+ // Don't replace a real comdat.
+ if (!F->getComdat()) {
+ llvm::Comdat *C = TheModule.getOrInsertComdat(F->getName());
+ C->setSelectionKind(llvm::Comdat::NoDeduplicate);
+ F->setComdat(C);
+ }
+ }
llvm::AttrBuilder Attrs(F->getContext());
if (GetCPUAndFeaturesAttributes(GD, Attrs)) {
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