[llvm] 9d55e4e - Make explicit -fno-semantic-interposition (in -fpic mode) infer dso_local
Fangrui Song via llvm-commits
llvm-commits at lists.llvm.org
Mon May 25 20:50:32 PDT 2020
Author: Fangrui Song
Date: 2020-05-25T20:48:18-07:00
New Revision: 9d55e4ee1367b440bb8402ce3a33d5a8b99aee06
URL: https://github.com/llvm/llvm-project/commit/9d55e4ee1367b440bb8402ce3a33d5a8b99aee06
DIFF: https://github.com/llvm/llvm-project/commit/9d55e4ee1367b440bb8402ce3a33d5a8b99aee06.diff
LOG: Make explicit -fno-semantic-interposition (in -fpic mode) infer dso_local
-fno-semantic-interposition is currently the CC1 default. (The opposite
disables some interprocedural optimizations.) However, it does not infer
dso_local: on most targets accesses to ExternalLinkage functions/variables
defined in the current module still need PLT/GOT.
This patch makes explicit -fno-semantic-interposition infer dso_local,
so that PLT/GOT can be eliminated if targets implement local aliases
for AsmPrinter::getSymbolPreferLocal (currently only x86).
Currently we check whether the module flag "SemanticInterposition" is 0.
If yes, infer dso_local. In the future, we can infer dso_local unless
"SemanticInterposition" is 1: frontends other than clang will also
benefit from the optimization if they don't bother setting the flag.
(There will be risks if they do want ELF interposition: they need to set
"SemanticInterposition" to 1.)
Added:
llvm/test/CodeGen/X86/semantic-interposition-infer-dsolocal.ll
Modified:
clang/include/clang/Basic/LangOptions.def
clang/include/clang/Driver/Options.td
clang/lib/CodeGen/CodeGenModule.cpp
clang/lib/Driver/ToolChains/Clang.cpp
clang/lib/Frontend/CompilerInvocation.cpp
clang/test/CodeGen/semantic-interposition.c
clang/test/Driver/fsemantic-interposition.c
llvm/include/llvm/IR/GlobalValue.h
llvm/include/llvm/IR/Module.h
llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
llvm/lib/IR/Globals.cpp
llvm/lib/IR/Module.cpp
llvm/lib/Target/TargetMachine.cpp
Removed:
################################################################################
diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
index e94305da46ba..6e72b47f489b 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -301,6 +301,7 @@ ENUM_LANGOPT(TypeVisibilityMode, Visibility, 3, DefaultVisibility,
LANGOPT(SetVisibilityForExternDecls, 1, 0,
"apply global symbol visibility to external declarations without an explicit visibility")
BENIGN_LANGOPT(SemanticInterposition , 1, 0, "semantic interposition")
+BENIGN_LANGOPT(ExplicitNoSemanticInterposition, 1, 0, "explicitly no semantic interposition")
ENUM_LANGOPT(StackProtector, StackProtectorMode, 2, SSPOff,
"stack protector mode")
ENUM_LANGOPT(TrivialAutoVarInit, TrivialAutoVarInitKind, 2, TrivialAutoVarInitKind::Uninitialized,
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 7213af1731c1..e88e6cf8a130 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3371,7 +3371,7 @@ defm ipa_cp : BooleanFFlag<"ipa-cp">,
Group<clang_ignored_gcc_optimization_f_Group>;
defm ivopts : BooleanFFlag<"ivopts">, Group<clang_ignored_gcc_optimization_f_Group>;
def fsemantic_interposition : Flag<["-"], "fsemantic-interposition">, Group<f_Group>, Flags<[CC1Option]>;
-def fno_semantic_interposition: Flag<["-"], "fno-semantic-interposition">, Group<f_Group>;
+def fno_semantic_interposition: Flag<["-"], "fno-semantic-interposition">, Group<f_Group>, Flags<[CC1Option]>;
defm non_call_exceptions : BooleanFFlag<"non-call-exceptions">, Group<clang_ignored_f_Group>;
defm peel_loops : BooleanFFlag<"peel-loops">, Group<clang_ignored_gcc_optimization_f_Group>;
defm permissive : BooleanFFlag<"permissive">, Group<clang_ignored_f_Group>;
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 8ba7fb756ada..f43bc6434daf 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -493,6 +493,9 @@ void CodeGenModule::Release() {
if (Context.getLangOpts().SemanticInterposition)
// Require various optimization to respect semantic interposition.
getModule().setSemanticInterposition(1);
+ else if (Context.getLangOpts().ExplicitNoSemanticInterposition)
+ // Allow dso_local on applicable targets.
+ getModule().setSemanticInterposition(0);
if (CodeGenOpts.EmitCodeView) {
// Indicate that we want CodeView in the metadata.
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index deb60ed68cfc..f33983db3e1e 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -4471,10 +4471,12 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
CmdArgs.push_back(A->getValue());
}
- if (Args.hasFlag(options::OPT_fsemantic_interposition,
- options::OPT_fno_semantic_interposition, false) &&
- RelocationModel != llvm::Reloc::Static && !IsPIE)
- CmdArgs.push_back("-fsemantic-interposition");
+ // The default is -fno-semantic-interposition. We render it just because we
+ // require explicit -fno-semantic-interposition to infer dso_local.
+ if (Arg *A = Args.getLastArg(options::OPT_fsemantic_interposition,
+ options::OPT_fno_semantic_interposition))
+ if (RelocationModel != llvm::Reloc::Static && !IsPIE)
+ A->render(Args, CmdArgs);
CmdArgs.push_back("-mthread-model");
if (Arg *A = Args.getLastArg(options::OPT_mthread_model)) {
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index b4bc027e832b..f98490cd9a11 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -3049,6 +3049,9 @@ static void ParseLangArgs(LangOptions &Opts, ArgList &Args, InputKind IK,
}
Opts.SemanticInterposition = Args.hasArg(OPT_fsemantic_interposition);
+ // An explicit -fno-semantic-interposition infers dso_local.
+ Opts.ExplicitNoSemanticInterposition =
+ Args.hasArg(OPT_fno_semantic_interposition);
// -mrtd option
if (Arg *A = Args.getLastArg(OPT_mrtd)) {
diff --git a/clang/test/CodeGen/semantic-interposition.c b/clang/test/CodeGen/semantic-interposition.c
index 43656e36021f..3d6c5f2872b5 100644
--- a/clang/test/CodeGen/semantic-interposition.c
+++ b/clang/test/CodeGen/semantic-interposition.c
@@ -1,5 +1,9 @@
// RUN: %clang_cc1 -emit-llvm -fsemantic-interposition %s -o - | FileCheck --check-prefix=INTERPOSITION %s
// RUN: %clang_cc1 -emit-llvm %s -o - | FileCheck --check-prefix=NO %s
+/// With explicit -fno-semantic-interposition, add a module flag to inform the
+/// backend that dso_local can be inferred.
+// RUN: %clang_cc1 -emit-llvm -fno-semantic-interposition %s -o - | FileCheck --check-prefix=EXPLICIT_NO %s
// INTERPOSITION: !{{[0-9]+}} = !{i32 1, !"SemanticInterposition", i32 1}
// NO-NOT: "SemanticInterposition"
+// EXPLICIT_NO: !{{[0-9]+}} = !{i32 1, !"SemanticInterposition", i32 0}
diff --git a/clang/test/Driver/fsemantic-interposition.c b/clang/test/Driver/fsemantic-interposition.c
index 20bc2c6f7270..af3e7575a799 100644
--- a/clang/test/Driver/fsemantic-interposition.c
+++ b/clang/test/Driver/fsemantic-interposition.c
@@ -2,8 +2,12 @@
// RUN: %clang -target x86_64 %s -Werror -fPIC -fsemantic-interposition -c -### 2>&1 | FileCheck %s
// CHECK: "-fsemantic-interposition"
-// RUN: %clang -target x86_64 %s -Werror -fPIC -fsemantic-interposition -fno-semantic-interposition -c -### 2>&1 | FileCheck --check-prefix=NO %s
+/// Require explicit -fno-semantic-interposition to infer dso_local.
+// RUN: %clang -target x86_64 %s -Werror -fPIC -fsemantic-interposition -fno-semantic-interposition -c -### 2>&1 | FileCheck --check-prefix=EXPLICIT_NO %s
+// EXPLICIT_NO: "-fno-semantic-interposition"
+
// RUN: %clang -target x86_64 %s -Werror -fsemantic-interposition -c -### 2>&1 | FileCheck --check-prefix=NO %s
// RUN: %clang -target x86_64 %s -Werror -fPIC -c -### 2>&1 | FileCheck --check-prefix=NO %s
// RUN: %clang -target x86_64 %s -Werror -fPIE -fsemantic-interposition -c -### 2>&1 | FileCheck --check-prefix=NO %s
// NO-NOT: "-fsemantic-interposition"
+// NO-NOT: "-fno-semantic-interposition"
diff --git a/llvm/include/llvm/IR/GlobalValue.h b/llvm/include/llvm/IR/GlobalValue.h
index 398eca2d9b2e..1c19011c9131 100644
--- a/llvm/include/llvm/IR/GlobalValue.h
+++ b/llvm/include/llvm/IR/GlobalValue.h
@@ -427,6 +427,7 @@ class GlobalValue : public Constant {
/// inlining across interposable call edges, since the callee can be
/// replaced with something arbitrary.
bool isInterposable() const;
+ bool canBenefitFromLocalAlias() const;
bool hasExternalLinkage() const { return isExternalLinkage(getLinkage()); }
bool hasAvailableExternallyLinkage() const {
diff --git a/llvm/include/llvm/IR/Module.h b/llvm/include/llvm/IR/Module.h
index 3052651a3722..ead003007904 100644
--- a/llvm/include/llvm/IR/Module.h
+++ b/llvm/include/llvm/IR/Module.h
@@ -857,6 +857,7 @@ class Module {
/// Returns whether semantic interposition is to be respected.
bool getSemanticInterposition() const;
+ bool noSemanticInterposition() const;
/// Set whether semantic interposition is to be respected.
void setSemanticInterposition(bool);
diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index db458e2b8a92..5fba0f01ba52 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -462,10 +462,10 @@ MCSymbol *AsmPrinter::getSymbolPreferLocal(const GlobalValue &GV) const {
// assembler would otherwise be conservative and assume a global default
// visibility symbol can be interposable, even if the code generator already
// assumed it.
- if (TM.getTargetTriple().isOSBinFormatELF() &&
- GlobalObject::isExternalLinkage(GV.getLinkage()) && GV.isDSOLocal() &&
- !GV.isDeclaration() && !isa<GlobalIFunc>(GV) && !GV.hasComdat())
- return getSymbolWithGlobalValueBase(&GV, "$local");
+ if (TM.getTargetTriple().isOSBinFormatELF() && GV.canBenefitFromLocalAlias())
+ if (GV.isDSOLocal() || (TM.getTargetTriple().isX86() &&
+ GV.getParent()->noSemanticInterposition()))
+ return getSymbolWithGlobalValueBase(&GV, "$local");
return TM.getSymbol(&GV);
}
diff --git a/llvm/lib/IR/Globals.cpp b/llvm/lib/IR/Globals.cpp
index 7c1c682d0262..eefd221ec389 100644
--- a/llvm/lib/IR/Globals.cpp
+++ b/llvm/lib/IR/Globals.cpp
@@ -101,6 +101,12 @@ bool GlobalValue::isInterposable() const {
!isDSOLocal();
}
+bool GlobalValue::canBenefitFromLocalAlias() const {
+ // See AsmPrinter::getSymbolPreferLocal().
+ return GlobalObject::isExternalLinkage(getLinkage()) && !isDeclaration() &&
+ !isa<GlobalIFunc>(this) && !hasComdat();
+}
+
unsigned GlobalValue::getAlignment() const {
if (auto *GA = dyn_cast<GlobalAlias>(this)) {
// In general we cannot compute this at the IR level, but we try.
diff --git a/llvm/lib/IR/Module.cpp b/llvm/lib/IR/Module.cpp
index 9ac1edb2519d..1416cdce9974 100644
--- a/llvm/lib/IR/Module.cpp
+++ b/llvm/lib/IR/Module.cpp
@@ -600,6 +600,13 @@ void Module::setSemanticInterposition(bool SI) {
addModuleFlag(ModFlagBehavior::Error, "SemanticInterposition", SI);
}
+bool Module::noSemanticInterposition() const {
+ // Conservatively require an explicit zero value for now.
+ Metadata *MF = getModuleFlag("SemanticInterposition");
+ auto *Val = cast_or_null<ConstantAsMetadata>(MF);
+ return Val && cast<ConstantInt>(Val->getValue())->getZExtValue() == 0;
+}
+
void Module::setOwnedMemoryBuffer(std::unique_ptr<MemoryBuffer> MB) {
OwnedMemoryBuffer = std::move(MB);
}
diff --git a/llvm/lib/Target/TargetMachine.cpp b/llvm/lib/Target/TargetMachine.cpp
index 1de6e871569c..074e9fde79e6 100644
--- a/llvm/lib/Target/TargetMachine.cpp
+++ b/llvm/lib/Target/TargetMachine.cpp
@@ -193,6 +193,14 @@ bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
// Check if we can use copy relocations.
if (!(GV && GV->isThreadLocal()) && RM == Reloc::Static)
return true;
+ } else if (TT.isOSBinFormatELF()) {
+ // If dso_local allows AsmPrinter::getSymbolPreferLocal to use a local
+ // alias, set the flag. We cannot set dso_local for other global values,
+ // because otherwise direct accesses to a probably interposable symbol (even
+ // if the codegen assumes not) will be rejected by the linker.
+ if (!GV || !GV->canBenefitFromLocalAlias())
+ return false;
+ return TT.isX86() && M.noSemanticInterposition();
}
// ELF & wasm support preemption of other symbols.
diff --git a/llvm/test/CodeGen/X86/semantic-interposition-infer-dsolocal.ll b/llvm/test/CodeGen/X86/semantic-interposition-infer-dsolocal.ll
new file mode 100644
index 000000000000..a0391d036468
--- /dev/null
+++ b/llvm/test/CodeGen/X86/semantic-interposition-infer-dsolocal.ll
@@ -0,0 +1,46 @@
+; RUN: llc -mtriple=x86_64 -relocation-model=pic < %s | FileCheck %s
+
+;; With a module flag SemanticInterposition=0, infer dso_local flags even if PIC.
+;; Local aliases will be generated for applicable variables and functions.
+
+ at var = global i32 0, align 4
+
+ at ifunc = ifunc i32 (), bitcast (i32 ()* ()* @ifunc_resolver to i32 ()*)
+
+define i32 @ifunc_impl() {
+entry:
+ ret i32 0
+}
+
+define i32 ()* @ifunc_resolver() {
+entry:
+ ret i32 ()* @ifunc_impl
+}
+
+declare i32 @external()
+
+define i32 @func() {
+ ret i32 0
+}
+
+;; Don't set dso_local on declarations or ifuncs.
+define i32 @foo() {
+; CHECK: movl .Lvar$local(%rip), %ebp
+; CHECK: callq external at PLT
+; CHECK: callq ifunc at PLT
+; CHECK: callq .Lfunc$local{{$}}
+entry:
+ %0 = load i32, i32* @var, align 4
+ %call = tail call i32 @external()
+ %add = add nsw i32 %call, %0
+ %call1 = tail call i32 @ifunc()
+ %add2 = add nsw i32 %add, %call1
+ %call2 = tail call i32 @func()
+ %add3 = add nsw i32 %add, %call2
+ ret i32 %add3
+}
+
+!llvm.module.flags = !{!0, !1}
+
+!0 = !{i32 1, !"SemanticInterposition", i32 0}
+!1 = !{i32 7, !"PIC Level", i32 2}
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