From 401e10c4fbfcdcfade5065093e2ca97f69a1d144 Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Mon, 20 Jul 2009 06:14:25 +0000 Subject: [PATCH] implement a new magic global "llvm.compiler.used" which is like llvm.used, but doesn't cause ".no_dead_strip" to be emitted on darwin. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76399 91177308-0d34-0410-b5e6-96231b3b80d8 --- docs/LangRef.html | 25 +++++++++++++-- include/llvm/CodeGen/MachineModuleInfo.h | 13 +++++--- lib/CodeGen/AsmPrinter/AsmPrinter.cpp | 4 +-- lib/CodeGen/AsmPrinter/DwarfException.cpp | 2 +- lib/CodeGen/MachineModuleInfo.cpp | 3 +- lib/Transforms/IPO/Internalize.cpp | 2 ++ lib/Transforms/IPO/StripSymbols.cpp | 37 ++++++++++------------- test/CodeGen/X86/compiler_used.ll | 9 ++++++ 8 files changed, 63 insertions(+), 32 deletions(-) create mode 100644 test/CodeGen/X86/compiler_used.ll diff --git a/docs/LangRef.html b/docs/LangRef.html index 910fc5c6514..dced11c4416 100644 --- a/docs/LangRef.html +++ b/docs/LangRef.html @@ -94,6 +94,8 @@
  • Intrinsic Global Variables
    1. The 'llvm.used' Global Variable
      2. +
    2. The 'llvm.compiler.used' + Global Variable
    3. The 'llvm.global_ctors' Global Variable
    4. The 'llvm.global_dtors' @@ -2168,8 +2170,9 @@ call void asm sideeffect "eieio", ""()

      LLVM has a number of "magic" global variables that contain data that affect code generation or other IR semantics. These are documented here. All globals -of this sort should have a section specified as "llvm.metadata". This section -and all globals that start with "llvm." are reserved for LLVM.

      +of this sort should have a section specified as "llvm.metadata". This +section and all globals that start with "llvm." are reserved for use +by LLVM.

      @@ -2206,6 +2209,24 @@ object file to prevent the assembler and linker from molesting the symbol.

      + +
      +The 'llvm.compiler.used' Global Variable +
      + +
      + +

      The @llvm.compiler.used directive is the same as the +@llvm.used directive, except that it only prevents the compiler from +touching the symbol. On targets that support it, this allows an intelligent +linker to optimize references to the symbol without being impeded as it would be +by @llvm.used.

      + +

      This is a rare construct that should only be used in rare circumstances, and +should not be exposed to source languages.

      + +
      +
      The 'llvm.global_ctors' Global Variable diff --git a/include/llvm/CodeGen/MachineModuleInfo.h b/include/llvm/CodeGen/MachineModuleInfo.h index 1872bd26d8a..3618898a79d 100644 --- a/include/llvm/CodeGen/MachineModuleInfo.h +++ b/include/llvm/CodeGen/MachineModuleInfo.h @@ -112,8 +112,9 @@ private: // common EH frames. std::vector Personalities; - // UsedFunctions - the functions in the llvm.used list in a more easily - // searchable format. + /// UsedFunctions - The functions in the @llvm.used list in a more easily + /// searchable format. This does not include the functions in + /// llvm.compiler.used. SmallPtrSet UsedFunctions; /// UsedDbgLabels - labels are used by debug info entries. @@ -240,9 +241,11 @@ public: return Personalities; } - // UsedFunctions - Return set of the functions in the llvm.used list. - const SmallPtrSet& getUsedFunctions() const { - return UsedFunctions; + /// isUsedFunction - Return true if the functions in the llvm.used list. This + /// does not return true for things in llvm.compiler.used unless they are also + /// in llvm.used. + bool isUsedFunction(const Function *F) { + return UsedFunctions.count(F); } /// addCatchTypeInfo - Provide the catch typeinfo for a landing pad. diff --git a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp index a2d154f1ee6..80bdf04e8e8 100644 --- a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp +++ b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp @@ -466,13 +466,13 @@ void AsmPrinter::printPICJumpTableEntry(const MachineJumpTableInfo *MJTI, /// special global used by LLVM. If so, emit it and return true, otherwise /// do nothing and return false. bool AsmPrinter::EmitSpecialLLVMGlobal(const GlobalVariable *GV) { - if (GV->getName() == "llvm.used") { + if (GV->isName("llvm.used")) { if (TAI->getUsedDirective() != 0) // No need to emit this at all. EmitLLVMUsedList(GV->getInitializer()); return true; } - // Ignore debug and non-emitted data. + // Ignore debug and non-emitted data. This handles llvm.compiler.used. if (GV->getSection() == "llvm.metadata" || GV->hasAvailableExternallyLinkage()) return true; diff --git a/lib/CodeGen/AsmPrinter/DwarfException.cpp b/lib/CodeGen/AsmPrinter/DwarfException.cpp index 1af3b118465..fdec97ac6ac 100644 --- a/lib/CodeGen/AsmPrinter/DwarfException.cpp +++ b/lib/CodeGen/AsmPrinter/DwarfException.cpp @@ -229,7 +229,7 @@ void DwarfException::EmitEHFrame(const FunctionEHFrameInfo &EHFrameInfo) { // retains the function in this case, and there is code around that depends // on unused functions (calling undefined externals) being dead-stripped to // link correctly. Yes, there really is. - if (MMI->getUsedFunctions().count(EHFrameInfo.function)) + if (MMI->isUsedFunction(EHFrameInfo.function)) if (const char *UsedDirective = TAI->getUsedDirective()) O << UsedDirective << EHFrameInfo.FnName << "\n\n"; } diff --git a/lib/CodeGen/MachineModuleInfo.cpp b/lib/CodeGen/MachineModuleInfo.cpp index 66dd8375eb5..20b819e8235 100644 --- a/lib/CodeGen/MachineModuleInfo.cpp +++ b/lib/CodeGen/MachineModuleInfo.cpp @@ -88,7 +88,8 @@ void MachineModuleInfo::EndFunction() { /// AnalyzeModule - Scan the module for global debug information. /// void MachineModuleInfo::AnalyzeModule(Module &M) { - // Insert functions in the llvm.used array into UsedFunctions. + // Insert functions in the llvm.used array (but not llvm.compiler.used) into + // UsedFunctions. GlobalVariable *GV = M.getGlobalVariable("llvm.used"); if (!GV || !GV->hasInitializer()) return; diff --git a/lib/Transforms/IPO/Internalize.cpp b/lib/Transforms/IPO/Internalize.cpp index 9bc91725170..da92634abf7 100644 --- a/lib/Transforms/IPO/Internalize.cpp +++ b/lib/Transforms/IPO/Internalize.cpp @@ -138,7 +138,9 @@ bool InternalizePass::runOnModule(Module &M) { // Never internalize the llvm.used symbol. It is used to implement // attribute((used)). + // FIXME: Shouldn't this just filter on llvm.metadata section?? ExternalNames.insert("llvm.used"); + ExternalNames.insert("llvm.compiler.used"); // Never internalize anchors used by the machine module info, else the info // won't find them. (see MachineModuleInfo.) diff --git a/lib/Transforms/IPO/StripSymbols.cpp b/lib/Transforms/IPO/StripSymbols.cpp index 82a0952aa20..8f3a7f4a649 100644 --- a/lib/Transforms/IPO/StripSymbols.cpp +++ b/lib/Transforms/IPO/StripSymbols.cpp @@ -157,32 +157,26 @@ static void StripTypeSymtab(TypeSymbolTable &ST, bool PreserveDbgInfo) { } /// Find values that are marked as llvm.used. -void findUsedValues(Module &M, - SmallPtrSet& llvmUsedValues) { - if (GlobalVariable *LLVMUsed = M.getGlobalVariable("llvm.used")) { - llvmUsedValues.insert(LLVMUsed); - // Collect values that are preserved as per explicit request. - // llvm.used is used to list these values. - if (ConstantArray *Inits = - dyn_cast(LLVMUsed->getInitializer())) { - for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i) { - if (GlobalValue *GV = dyn_cast(Inits->getOperand(i))) - llvmUsedValues.insert(GV); - else if (ConstantExpr *CE = - dyn_cast(Inits->getOperand(i))) - if (CE->getOpcode() == Instruction::BitCast) - if (GlobalValue *GV = dyn_cast(CE->getOperand(0))) - llvmUsedValues.insert(GV); - } - } - } +static void findUsedValues(GlobalVariable *LLVMUsed, + SmallPtrSet &UsedValues) { + if (LLVMUsed == 0) return; + UsedValues.insert(LLVMUsed); + + ConstantArray *Inits = dyn_cast(LLVMUsed->getInitializer()); + if (Inits == 0) return; + + for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i) + if (GlobalValue *GV = + dyn_cast(Inits->getOperand(i)->stripPointerCasts())) + UsedValues.insert(GV); } /// StripSymbolNames - Strip symbol names. bool StripSymbolNames(Module &M, bool PreserveDbgInfo) { SmallPtrSet llvmUsedValues; - findUsedValues(M, llvmUsedValues); + findUsedValues(M.getGlobalVariable("llvm.used"), llvmUsedValues); + findUsedValues(M.getGlobalVariable("llvm.compiler.used"), llvmUsedValues); for (Module::global_iterator I = M.global_begin(), E = M.global_end(); I != E; ++I) { @@ -210,7 +204,8 @@ bool StripSymbolNames(Module &M, bool PreserveDbgInfo) { bool StripDebugInfo(Module &M) { SmallPtrSet llvmUsedValues; - findUsedValues(M, llvmUsedValues); + findUsedValues(M.getGlobalVariable("llvm.used"), llvmUsedValues); + findUsedValues(M.getGlobalVariable("llvm.compiler.used"), llvmUsedValues); SmallVector CUs; SmallVector GVs; diff --git a/test/CodeGen/X86/compiler_used.ll b/test/CodeGen/X86/compiler_used.ll new file mode 100644 index 00000000000..b67bc36d507 --- /dev/null +++ b/test/CodeGen/X86/compiler_used.ll @@ -0,0 +1,9 @@ +; RUN: llvm-as < %s | llc -mtriple=i386-apple-darwin9 | grep no_dead_strip | count 1 +; We should have a .no_dead_strip directive for Z but not for X/Y. + +@X = internal global i8 4 +@Y = internal global i32 123 +@Z = internal global i8 4 + +@llvm.used = appending global [1 x i8*] [ i8* @Z ], section "llvm.metadata" +@llvm.compiler_used = appending global [2 x i8*] [ i8* @X, i8* bitcast (i32* @Y to i8*)], section "llvm.metadata" -- 2.34.1