Prazek created this revision.
Prazek added reviewers: rjmccall, rsmith, amharc, kuhar.
Herald added a subscriber: llvm-commits.
In many cases we can't devirtualize
because definition of vtable is not present. Most of the
time it is caused by inline virtual function not beeing
emitted. Forcing emitting of vtable adds a reference of these
inline virtual functions
Repository:
rL LLVM
https://reviews.llvm.org/D47108
Files:
clang/docs/ClangCommandLineReference.rst
clang/docs/UsersManual.rst
clang/include/clang/Driver/Options.td
clang/include/clang/Frontend/CodeGenOptions.def
clang/lib/CodeGen/ItaniumCXXABI.cpp
clang/lib/Driver/ToolChains/Clang.cpp
clang/lib/Frontend/CompilerInvocation.cpp
clang/test/CodeGenCXX/vtable-available-externally.cpp
clang/test/CodeGenCXX/vtable-linkage.cpp
Index: clang/test/CodeGenCXX/vtable-linkage.cpp
===================================================================
--- clang/test/CodeGenCXX/vtable-linkage.cpp
+++ clang/test/CodeGenCXX/vtable-linkage.cpp
@@ -1,11 +1,13 @@
// RUN: %clang_cc1 %s -triple=x86_64-pc-linux -emit-llvm -o %t
// RUN: %clang_cc1 %s -triple=x86_64-pc-linux -emit-llvm -std=c++03 -o %t.03
// RUN: %clang_cc1 %s -triple=x86_64-pc-linux -emit-llvm -std=c++11 -o %t.11
+// RUN: %clang_cc1 %s -triple=x86_64-pc-linux -emit-llvm -std=c++11 -o %t.vtables -fforce-emit-vtables -O3
// RUN: %clang_cc1 %s -triple=x86_64-apple-darwin10 -disable-llvm-passes -O3 -emit-llvm -o %t.opt
// RUN: FileCheck %s < %t
// RUN: FileCheck %s < %t.03
// RUN: FileCheck %s < %t.11
// RUN: FileCheck --check-prefix=CHECK-OPT %s < %t.opt
+// RUN: FileCheck --check-prefix=CHECK-OPT %s < %t.vtables
namespace {
struct A {
Index: clang/test/CodeGenCXX/vtable-available-externally.cpp
===================================================================
--- clang/test/CodeGenCXX/vtable-available-externally.cpp
+++ clang/test/CodeGenCXX/vtable-available-externally.cpp
@@ -1,5 +1,6 @@
// RUN: %clang_cc1 %s -I%S -triple=x86_64-apple-darwin10 -std=c++98 -emit-llvm -o %t
// RUN: %clang_cc1 %s -I%S -triple=x86_64-apple-darwin10 -std=c++98 -O2 -disable-llvm-passes -emit-llvm -o %t.opt
+// RUN: %clang_cc1 %s -I%S -triple=x86_64-apple-darwin10 -std=c++98 -O2 -disable-llvm-passes -emit-llvm -o %t.vtable -fforce-emit-vtables
// RUN: FileCheck --check-prefix=CHECK-TEST1 %s < %t
// RUN: FileCheck --check-prefix=CHECK-TEST2 %s < %t
// RUN: FileCheck --check-prefix=CHECK-TEST5 %s < %t
@@ -13,10 +14,13 @@
// RUN: FileCheck --check-prefix=CHECK-TEST15 %s < %t.opt
// RUN: FileCheck --check-prefix=CHECK-TEST16 %s < %t.opt
// RUN: FileCheck --check-prefix=CHECK-TEST17 %s < %t.opt
+// RUN: FileCheck --check-prefix=CHECK-FORCE-EMIT %s < %t.vtable
+
#include <typeinfo>
// CHECK-TEST1: @_ZTVN5Test11AE = external unnamed_addr constant
+// CHECK-FORCE-EMIT-DAG: @_ZTVN5Test11AE = available_externally unnamed_addr constant
namespace Test1 {
struct A {
@@ -213,14 +217,16 @@
// because A's key function is defined here, vtable is generated in this TU
// CHECK-TEST10-DAG: @_ZTVN6Test101AE = unnamed_addr constant
+// CHECK-FORCE-EMIT-DAG: @_ZTVN6Test101AE = unnamed_addr constant
struct A {
virtual void foo();
virtual void bar();
};
void A::foo() {}
// Because key function is inline we will generate vtable as linkonce_odr.
// CHECK-TEST10-DAG: @_ZTVN6Test101DE = linkonce_odr unnamed_addr constant
+// CHECK-FORCE-EMIT-DAG: @_ZTVN6Test101DE = linkonce_odr unnamed_addr constant
struct D : A {
void bar();
};
@@ -237,14 +243,17 @@
// can't guarantee that we will be able to refer to bar from name
// so (at the moment) we can't emit vtable available_externally.
// CHECK-TEST10-DAG: @_ZTVN6Test101CE = external unnamed_addr constant
+// CHECK-FORCE-EMIT-DAG: @_ZTVN6Test101CE = available_externally unnamed_addr constant
struct C : A {
void bar() {} // defined in body - not key function
virtual inline void gar(); // inline in body - not key function
virtual void car();
};
// no key function, vtable will be generated everywhere it will be used
// CHECK-TEST10-DAG: @_ZTVN6Test101EE = linkonce_odr unnamed_addr constant
+// CHECK-FORCE-EMIT-DAG: @_ZTVN6Test101EE = linkonce_odr unnamed_addr constant
+
struct E : A {};
void g(A& a) {
@@ -298,11 +307,13 @@
namespace Test12 {
// CHECK-TEST12: @_ZTVN6Test121AE = external unnamed_addr constant
+// CHECK-FORCE-EMIT-DAG: @_ZTVN6Test121AE = available_externally unnamed_addr constant
struct A {
virtual void foo();
virtual ~A() {}
};
// CHECK-TEST12: @_ZTVN6Test121BE = external unnamed_addr constant
+// CHECK-FORCE-EMIT-DAG: @_ZTVN6Test121BE = available_externally unnamed_addr constant
struct B : A {
void foo();
};
@@ -319,6 +330,9 @@
// CHECK-TEST13-DAG: @_ZTVN6Test131AE = available_externally unnamed_addr constant
// CHECK-TEST13-DAG: @_ZTVN6Test131BE = external unnamed_addr constant
+// CHECK-FORCE-EMIT-DAG: @_ZTVN6Test131AE = available_externally unnamed_addr constant
+// CHECK-FORCE-EMIT-DAG: @_ZTVN6Test131BE = available_externally unnamed_addr constant
+
struct A {
virtual ~A();
};
@@ -371,6 +385,8 @@
// generate available_externally vtable for it.
// CHECK-TEST16-DAG: @_ZTVN6Test161SE = external unnamed_addr constant
// CHECK-TEST16-DAG: @_ZTVN6Test162S2E = available_externally
+// CHECK-FORCE-EMIT-DAG: @_ZTVN6Test161SE = external unnamed_addr constant
+// CHECK-FORCE-EMIT-DAG: @_ZTVN6Test162S2E = available_externally
struct S {
__attribute__((visibility("hidden"))) virtual void doStuff();
@@ -395,6 +411,10 @@
// This test checks if we emit vtables opportunistically.
// CHECK-TEST17-DAG: @_ZTVN6Test171AE = available_externally
// CHECK-TEST17-DAG: @_ZTVN6Test171BE = external
+// CHECK-FORCE-EMIT-DAG: @_ZTVN6Test171AE = available_externally
+// CHECK-FORCE-EMIT-DAG: @_ZTVN6Test171BE = available_externally
+// CHECK-FORCE-EMIT-DAG: define linkonce_odr void @_ZN6Test171BD1Ev(
+// CHECK-FORCE-EMIT-DAG: define linkonce_odr void @_ZN6Test171BD0Ev(
struct A {
virtual void key();
Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -719,6 +719,7 @@
Opts.StrictEnums = Args.hasArg(OPT_fstrict_enums);
Opts.StrictReturn = !Args.hasArg(OPT_fno_strict_return);
Opts.StrictVTablePointers = Args.hasArg(OPT_fstrict_vtable_pointers);
+ Opts.ForceEmitVTables = Args.hasArg(OPT_fforce_emit_vtables);
Opts.UnsafeFPMath = Args.hasArg(OPT_menable_unsafe_fp_math) ||
Args.hasArg(OPT_cl_unsafe_math_optimizations) ||
Args.hasArg(OPT_cl_fast_relaxed_math);
Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -3472,6 +3472,10 @@
options::OPT_fno_strict_vtable_pointers,
false))
CmdArgs.push_back("-fstrict-vtable-pointers");
+ if (Args.hasFlag(options::OPT_fforce_emit_vtables,
+ options::OPT_fno_force_emit_vtables,
+ false))
+ CmdArgs.push_back("-fforce-emit-vtable");
if (!Args.hasFlag(options::OPT_foptimize_sibling_calls,
options::OPT_fno_optimize_sibling_calls))
CmdArgs.push_back("-mdisable-tail-calls");
Index: clang/lib/CodeGen/ItaniumCXXABI.cpp
===================================================================
--- clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -1706,11 +1706,19 @@
if (CGM.getLangOpts().AppleKext)
return false;
- // If we don't have any not emitted inline virtual function, and if vtable is
- // not hidden, then we are safe to emit available_externally copy of vtable.
+ // If vtable is hidden then it is not safe to emit available_externally
+ // copy of vtable.
+ if (isVTableHidden(RD))
+ return false;
+
+ if (CGM.getCodeGenOpts().ForceEmitVTables)
+ return true;
+
+ // If we don't have any not emitted inline virtual function then we are safe
+ // to emit available_externally copy of vtable.
// FIXME we can still emit a copy of the vtable if we
// can emit definition of the inline functions.
- return !hasAnyUnusedVirtualInlineFunction(RD) && !isVTableHidden(RD);
+ return !hasAnyUnusedVirtualInlineFunction(RD);
}
static llvm::Value *performTypeAdjustment(CodeGenFunction &CGF,
Address InitialPtr,
Index: clang/include/clang/Frontend/CodeGenOptions.def
===================================================================
--- clang/include/clang/Frontend/CodeGenOptions.def
+++ clang/include/clang/Frontend/CodeGenOptions.def
@@ -332,6 +332,10 @@
/// Whether to embed source in DWARF debug line section.
CODEGENOPT(EmbedSource, 1, 0)
+/// Whether to emit all vtables
+CODEGENOPT(ForceEmitVTables, 1, 0)
+
+
#undef CODEGENOPT
#undef ENUM_CODEGENOPT
#undef VALUE_CODEGENOPT
Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -1669,6 +1669,11 @@
HelpText<"Enables whole-program vtable optimization. Requires -flto">;
def fno_whole_program_vtables : Flag<["-"], "fno-whole-program-vtables">, Group<f_Group>,
Flags<[CoreOption]>;
+def fforce_emit_vtables : Flag<["-"], "fforce-emit-vtables">, Group<f_Group>,
+ Flags<[CC1Option]>,
+ HelpText<"Emits more virtual tables to improve devirtualization">;
+def fno_force_emit_vtables : Flag<["-"], "fno-force-emit-vtables">, Group<f_Group>,
+ Flags<[CoreOption]>;
def fwrapv : Flag<["-"], "fwrapv">, Group<f_Group>, Flags<[CC1Option]>,
HelpText<"Treat signed integer overflow as two's complement">;
def fwritable_strings : Flag<["-"], "fwritable-strings">, Group<f_Group>, Flags<[CC1Option]>,
Index: clang/docs/UsersManual.rst
===================================================================
--- clang/docs/UsersManual.rst
+++ clang/docs/UsersManual.rst
@@ -1269,6 +1269,12 @@
devirtualization and virtual constant propagation, for classes with
:doc:`hidden LTO visibility <LTOVisibility>`. Requires ``-flto``.
+.. option:: -fforce-emit-vtables
+
+ In order to improve devirtualization, forces emitting of vtables even in
+ modules where it isn't necessary. It causes more inline virtual functions
+ to be emitted.
+
.. option:: -fno-assume-sane-operator-new
Don't assume that the C++'s new operator is sane.
Index: clang/docs/ClangCommandLineReference.rst
===================================================================
--- clang/docs/ClangCommandLineReference.rst
+++ clang/docs/ClangCommandLineReference.rst
@@ -1934,6 +1934,12 @@
Enables whole-program vtable optimization. Requires -flto
+.. option:: -fforce-emit-vtables, -fno-force-emit-vtables
+
+In order to improve devirtualization, forces emitting of vtables even in
+modules where it isn't necessary. It causes more inline virtual functions
+to be emitted.
+
.. option:: -fwrapv, -fno-wrapv
Treat signed integer overflow as two's complement
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