Rebased PNaCl localmods in LLVM to 223109

lib/Transforms/NaCl/StripAttributes.cpp

+//===- StripAttributes.cpp - Remove attributes not supported by PNaCl------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass strips out attributes that are not supported by PNaCl's
+// stable ABI.  Currently, this strips out:
+//
+//  * Function and argument attributes from functions and function
+//    calls.
+//  * Calling conventions from functions and function calls.
+//  * The "align" attribute on functions.
+//  * The alignment argument of memcpy/memmove/memset intrinsic calls.
+//  * The "unnamed_addr" attribute on functions and global variables.
+//  * The distinction between "internal" and "private" linkage.
+//  * "protected" and "internal" visibility of functions and globals.
+//  * All sections are stripped. A few sections cause warnings.
+//  * The arithmetic attributes "nsw", "nuw" and "exact".
+//  * It reduces the set of possible "align" attributes on memory
+//    accesses.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Operator.h"
+#include "llvm/Pass.h"
+#include "llvm/IR/CallSite.h"
+#include "llvm/Transforms/NaCl.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+namespace {
+  // This is a ModulePass so that it can modify attributes of global
+  // variables.
+  class StripAttributes : public ModulePass {
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    StripAttributes() : ModulePass(ID) {
+      initializeStripAttributesPass(*PassRegistry::getPassRegistry());
+    }
+
+    virtual bool runOnModule(Module &M);
+  };
+}
+
+char StripAttributes::ID = 0;
+INITIALIZE_PASS(StripAttributes, "nacl-strip-attributes",
+                "Strip out attributes that are not part of PNaCl's ABI",
+                false, false)
+
+static void CheckAttributes(AttributeSet Attrs) {
+  for (unsigned Slot = 0; Slot < Attrs.getNumSlots(); ++Slot) {
+    for (AttributeSet::iterator Attr = Attrs.begin(Slot), E = Attrs.end(Slot);
+         Attr != E; ++Attr) {
+      if (!Attr->isEnumAttribute()) {
+        continue;
+      }
+      switch (Attr->getKindAsEnum()) {
+        // The vast majority of attributes are hints that can safely
+        // be removed, so don't complain if we see attributes we don't
+        // recognize.
+        default:
+
+        // The following attributes can affect calling conventions.
+        // Rather than complaining, we just strip these out.
+        // ExpandSmallArguments should have rendered SExt/ZExt
+        // meaningless since the function arguments will be at least
+        // 32-bit.
+        case Attribute::InReg:
+        case Attribute::SExt:
+        case Attribute::ZExt:
+        // These attributes influence ABI decisions that should not be
+        // visible to PNaCl pexes.
+        case Attribute::NonLazyBind:  // Only relevant to dynamic linking.
+        case Attribute::NoRedZone:
+        case Attribute::StackAlignment:
+
+        // The following attributes are just hints, which can be
+        // safely removed.
+        case Attribute::AlwaysInline:
+        case Attribute::InlineHint:
+        case Attribute::MinSize:
+        case Attribute::NoAlias:
+        case Attribute::NoBuiltin:
+        case Attribute::NoCapture:
+        case Attribute::NoDuplicate:
+        case Attribute::NoImplicitFloat:
+        case Attribute::NoInline:
+        case Attribute::NoReturn:
+        case Attribute::OptimizeForSize:
+        case Attribute::ReadNone:
+        case Attribute::ReadOnly:
+
+        // PNaCl does not support -fstack-protector in the translator.
+        case Attribute::StackProtect:
+        case Attribute::StackProtectReq:
+        case Attribute::StackProtectStrong:
+        // PNaCl does not support ASan in the translator.
+        case Attribute::SanitizeAddress:
+        case Attribute::SanitizeThread:
+        case Attribute::SanitizeMemory:
+
+        // The Language References cites setjmp() as an example of a
+        // function which returns twice, and says ReturnsTwice is
+        // necessary to disable optimizations such as tail calls.
+        // However, in the PNaCl ABI, setjmp() is an intrinsic, and
+        // user-defined functions are not allowed to return twice.
+        case Attribute::ReturnsTwice:
+
+        // NoUnwind is not a hint if it causes unwind info to be
+        // omitted, since this will prevent C++ exceptions from
+        // propagating.  In the future, when PNaCl supports zero-cost
+        // C++ exception handling using unwind info, we might allow
+        // NoUnwind and UWTable.  Alternatively, we might continue to
+        // disallow them, and just generate unwind info for all
+        // functions.
+        case Attribute::NoUnwind:
+        case Attribute::UWTable:
+          break;
+
+        // A few attributes can change program behaviour if removed,
+        // so check for these.
+        case Attribute::ByVal:
+        case Attribute::StructRet:
+        case Attribute::Alignment:
+          Attrs.dump();
+          report_fatal_error(
+              "Attribute should already have been removed by ExpandByVal");
+
+        case Attribute::Naked:
+        case Attribute::Nest:
+          Attrs.dump();
+          report_fatal_error("Unsupported attribute");
+      }
+    }
+  }
+}
+
+static const char* ShouldWarnAboutSection(const char* Section) {
+  static const char* SpecialSections[] = {
+    ".init_array",
+    ".init",
+    ".fini_array",
+    ".fini",
+
+    // Java/LSB:
+    ".jcr",
+
+    // LSB:
+    ".ctors",
+    ".dtors",
+  };
+
+  for (auto CheckSection : SpecialSections) {
+    if (strcmp(Section, CheckSection) == 0) {
+      return CheckSection;
+    }
+  }
+
+  return nullptr;
+}
+
+void stripGlobalValueAttrs(GlobalValue *GV) {
+  // In case source code uses __attribute__((visibility("hidden"))) or
+  // __attribute__((visibility("protected"))), strip these attributes.
+  GV->setVisibility(GlobalValue::DefaultVisibility);
+
+  GV->setUnnamedAddr(false);
+
+  if (GV->hasSection()) {
+    const char *Section = GV->getSection();
+    // check for a few special cases
+    if (const char *WarnSection = ShouldWarnAboutSection(Section)) {
+      errs() << "Warning: " << GV->getName() <<
+        " will have its section (" <<
+        WarnSection << ") stripped.\n";
+    }
+
+    if(GlobalObject* GO = dyn_cast<GlobalObject>(GV)) {
+      GO->setSection("");
+    }
+    // Nothing we can do if GV isn't a GlobalObject.
+  }
+
+  // Convert "private" linkage to "internal" to reduce the number of
+  // linkage types that need to be represented in PNaCl's wire format.
+  //
+  // We convert "private" to "internal" rather than vice versa because
+  // "private" symbols are omitted from the nexe's symbol table, which
+  // would get in the way of debugging when an unstripped pexe is
+  // translated offline.
+  if (GV->getLinkage() == GlobalValue::PrivateLinkage)
+    GV->setLinkage(GlobalValue::InternalLinkage);
+}
+
+static unsigned normalizeAlignment(DataLayout *DL, unsigned Alignment,
+                                   Type *Ty, bool IsAtomic) {
+  unsigned MaxAllowed = 1;
+  if (isa<VectorType>(Ty))
+    // Already handled properly by FixVectorLoadStoreAlignment.
+    return Alignment;
+  if (Ty->isDoubleTy() || Ty->isFloatTy() || IsAtomic)
+    MaxAllowed = DL->getTypeAllocSize(Ty);
+  // If the alignment is set to 0, this means "use the default
+  // alignment for the target", which we fill in explicitly.
+  if (Alignment == 0 || Alignment >= MaxAllowed)
+    return MaxAllowed;
+  return 1;
+}
+
+void stripFunctionAttrs(DataLayout *DL, Function *Func) {
+  CheckAttributes(Func->getAttributes());
+  Func->setAttributes(AttributeSet());
+  Func->setCallingConv(CallingConv::C);
+  Func->setAlignment(0);
+
+  for (Function::iterator BB = Func->begin(), E = Func->end();
+       BB != E; ++BB) {
+    for (BasicBlock::iterator Inst = BB->begin(), E = BB->end();
+         Inst != E; ++Inst) {
+      CallSite Call(Inst);
+      if (Call) {
+        CheckAttributes(Call.getAttributes());
+        Call.setAttributes(AttributeSet());
+        Call.setCallingConv(CallingConv::C);
+
+        // Set memcpy(), memmove() and memset() to use pessimistic
+        // alignment assumptions.
+        if (MemIntrinsic *MemOp = dyn_cast<MemIntrinsic>(Inst)) {
+          Type *AlignTy = MemOp->getAlignmentCst()->getType();
+          MemOp->setAlignment(ConstantInt::get(AlignTy, 1));
+        }
+      } else if (OverflowingBinaryOperator *Op =
+                     dyn_cast<OverflowingBinaryOperator>(Inst)) {
+        cast<BinaryOperator>(Op)->setHasNoUnsignedWrap(false);
+        cast<BinaryOperator>(Op)->setHasNoSignedWrap(false);
+      } else if (PossiblyExactOperator *Op =
+                     dyn_cast<PossiblyExactOperator>(Inst)) {
+        cast<BinaryOperator>(Op)->setIsExact(false);
+      } else if (LoadInst *Load = dyn_cast<LoadInst>(Inst)) {
+        Load->setAlignment(normalizeAlignment(
+                               DL, Load->getAlignment(),
+                               Load->getType(),
+                               Load->isAtomic()));
+      } else if (StoreInst *Store = dyn_cast<StoreInst>(Inst)) {
+        Store->setAlignment(normalizeAlignment(
+                                DL, Store->getAlignment(),
+                                Store->getValueOperand()->getType(),
+                                Store->isAtomic()));
+      }
+    }
+  }
+}
+
+bool StripAttributes::runOnModule(Module &M) {
+  DataLayout DL(&M);
+  for (Module::iterator Func = M.begin(), E = M.end(); Func != E; ++Func) {
+    // Avoid stripping attributes from intrinsics because the
+    // constructor for Functions just adds them back again.  It would
+    // be confusing if the attributes were sometimes present on
+    // intrinsics and sometimes not.
+    if (!Func->isIntrinsic()) {
+      stripGlobalValueAttrs(Func);
+      stripFunctionAttrs(&DL, Func);
+    }
+  }
+  for (Module::global_iterator GV = M.global_begin(), E = M.global_end();
+       GV != E; ++GV) {
+    stripGlobalValueAttrs(GV);
+  }
+  return true;
+}
+
+ModulePass *llvm::createStripAttributesPass() {
+  return new StripAttributes();
+}