serge-sans-paille created this revision.
serge-sans-paille added reviewers: MaskRay, hfinkel.
Herald added subscribers: llvm-commits, cfe-commits, haicheng, hiraditya,
eraman.
Herald added projects: clang, LLVM.
serge-sans-paille added a comment.
@MaskRay no example yet, I'd like your opinion on the approach first. It has
the advantage of being non intrusive to the code base...
First attempt at implementing -fsemantic-interposition.
Rely on `GlobalValue::isInterposable` that already captures most of the
expected behavior.
Rely on a `ModuleFlag` to state whether we should respect SemanticInterposition
or not. The default remains no.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D72829
Files:
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
llvm/include/llvm/IR/GlobalValue.h
llvm/include/llvm/IR/Module.h
llvm/lib/Analysis/InlineCost.cpp
llvm/lib/IR/Globals.cpp
llvm/lib/IR/Module.cpp
Index: llvm/lib/IR/Module.cpp
===================================================================
--- llvm/lib/IR/Module.cpp
+++ llvm/lib/IR/Module.cpp
@@ -559,6 +559,20 @@
: getModuleFlag("ProfileSummary"));
}
+bool Module::getSemanticInterposition() const {
+ auto *Val =
+ cast_or_null<ConstantAsMetadata>(getModuleFlag("SemanticInterposition"));
+
+ if (!Val)
+ return false;
+
+ return cast<ConstantInt>(Val->getValue())->getZExtValue();
+}
+
+void Module::setSemanticInterposition(bool SI) {
+ addModuleFlag(ModFlagBehavior::Error, "SemanticInterposition", SI);
+}
+
void Module::setOwnedMemoryBuffer(std::unique_ptr<MemoryBuffer> MB) {
OwnedMemoryBuffer = std::move(MB);
}
Index: llvm/lib/IR/Globals.cpp
===================================================================
--- llvm/lib/IR/Globals.cpp
+++ llvm/lib/IR/Globals.cpp
@@ -94,6 +94,13 @@
llvm_unreachable("not a global");
}
+bool GlobalValue::isInterposable() const {
+ if (getParent() && getParent()->getSemanticInterposition() &&
+ isDSOPreemptable())
+ return true;
+ return isInterposableLinkage(getLinkage());
+}
+
unsigned GlobalValue::getAlignment() const {
if (auto *GA = dyn_cast<GlobalAlias>(this)) {
// In general we cannot compute this at the IR level, but we try.
Index: llvm/lib/Analysis/InlineCost.cpp
===================================================================
--- llvm/lib/Analysis/InlineCost.cpp
+++ llvm/lib/Analysis/InlineCost.cpp
@@ -1842,7 +1842,7 @@
} else if (Operator::getOpcode(V) == Instruction::BitCast) {
V = cast<Operator>(V)->getOperand(0);
} else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
- if (GA->isInterposable())
+ if (GA->isInterposable() || GA->isDSOPreemptable())
break;
V = GA->getAliasee();
} else {
Index: llvm/include/llvm/IR/Module.h
===================================================================
--- llvm/include/llvm/IR/Module.h
+++ llvm/include/llvm/IR/Module.h
@@ -846,6 +846,17 @@
Metadata *getProfileSummary(bool IsCS);
/// @}
+ /// @name Utility functions for querying and setting semantic interposition
+ /// @{
+
+ /// Returns whether semantic interposition is to be respected.
+ bool getSemanticInterposition() const;
+
+ /// Set whether semantic interposition is to be respected.
+ void setSemanticInterposition(bool);
+
+ /// @}
+
/// Returns true if PLT should be avoided for RTLib calls.
bool getRtLibUseGOT() const;
Index: llvm/include/llvm/IR/GlobalValue.h
===================================================================
--- llvm/include/llvm/IR/GlobalValue.h
+++ llvm/include/llvm/IR/GlobalValue.h
@@ -284,6 +284,8 @@
return IsDSOLocal;
}
+ bool isDSOPreemptable() const { return !IsDSOLocal; }
+
bool hasPartition() const {
return HasPartition;
}
@@ -426,7 +428,7 @@
/// *arbitrary* definition at link time. We cannot do any IPO or inlinining
/// across interposable call edges, since the callee can be replaced with
/// something arbitrary at link time.
- bool isInterposable() const { return isInterposableLinkage(getLinkage()); }
+ bool isInterposable() const;
bool hasExternalLinkage() const { return isExternalLinkage(getLinkage()); }
bool hasAvailableExternallyLinkage() const {
Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -2679,6 +2679,13 @@
Opts.setValueVisibilityMode(DefaultVisibility);
}
+ // Semantic interposition mode defaults to "false".
+ if (Arg *siOpt = Args.getLastArg(OPT_fsemantic_interposition,
+ OPT_fno_semantic_interposition)) {
+ Opts.SemanticInterposition =
+ unsigned(siOpt->getOption().getID() == OPT_fsemantic_interposition);
+ }
+
// The type-visibility mode defaults to the value-visibility mode.
if (Arg *typeVisOpt = Args.getLastArg(OPT_ftype_visibility)) {
Opts.setTypeVisibilityMode(parseVisibility(typeVisOpt, Args, Diags));
Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -5002,6 +5002,8 @@
Args.AddLastArg(CmdArgs, options::OPT_femulated_tls,
options::OPT_fno_emulated_tls);
Args.AddLastArg(CmdArgs, options::OPT_fkeep_static_consts);
+ Args.AddLastArg(CmdArgs, options::OPT_fsemantic_interposition,
+ options::OPT_fno_semantic_interposition);
// AltiVec-like language extensions aren't relevant for assembling.
if (!isa<PreprocessJobAction>(JA) || Output.getType() != types::TY_PP_Asm)
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -483,6 +483,11 @@
getModule().addModuleFlag(llvm::Module::Max, "Dwarf Version",
CodeGenOpts.DwarfVersion);
}
+
+ if (Context.getLangOpts().SemanticInterposition)
+ // Require various optimization to respect semantic interposition.
+ getModule().setSemanticInterposition(1);
+
if (CodeGenOpts.EmitCodeView) {
// Indicate that we want CodeView in the metadata.
getModule().addModuleFlag(llvm::Module::Warning, "CodeView", 1);
@@ -856,7 +861,7 @@
if (isa<llvm::Function>(GV) && !CGOpts.NoPLT && RM == llvm::Reloc::Static)
return true;
- // Otherwise don't assue it is local.
+ // Otherwise don't assume it is local.
return false;
}
Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -3262,7 +3262,8 @@
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 : Flag<["-"], "fno-semantic-interposition">, Group<clang_ignored_f_Group>;
+def fsemantic_interposition : Flag<["-"], "fsemantic-interposition">, Group<f_Group>, Flags<[CC1Option]>;
+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>;
Index: clang/include/clang/Basic/LangOptions.def
===================================================================
--- clang/include/clang/Basic/LangOptions.def
+++ clang/include/clang/Basic/LangOptions.def
@@ -284,6 +284,7 @@
"default visibility for types [-ftype-visibility]")
LANGOPT(SetVisibilityForExternDecls, 1, 0,
"apply global symbol visibility to external declarations without an explicit visibility")
+BENIGN_LANGOPT(SemanticInterposition , 1, 0, "semantic interposition")
ENUM_LANGOPT(StackProtector, StackProtectorMode, 2, SSPOff,
"stack protector mode")
ENUM_LANGOPT(TrivialAutoVarInit, TrivialAutoVarInitKind, 2, TrivialAutoVarInitKind::Uninitialized,
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