[llvm] r247080 - LowerBitSets: Extend pass to support functions as bitset members.
Rafael Espíndola via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 9 05:23:39 PDT 2015
Looks like some bots are still broken by this:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap
On 8 September 2015 at 17:57, Peter Collingbourne via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: pcc
> Date: Tue Sep 8 16:57:45 2015
> New Revision: 247080
>
> URL: http://llvm.org/viewvc/llvm-project?rev=247080&view=rev
> Log:
> LowerBitSets: Extend pass to support functions as bitset members.
>
> This change extends the bitset lowering pass to support bitsets that may
> contain either functions or global variables. A function bitset is lowered to
> a jump table that is laid out before one of the functions in the bitset.
>
> Also add support for non-string bitset identifier names. This allows for
> distinct metadata nodes to stand in for names with internal linkage,
> as done in D11857.
>
> Differential Revision: http://reviews.llvm.org/D11856
>
> Added:
> llvm/trunk/test/Transforms/LowerBitSets/function-ext.ll
> llvm/trunk/test/Transforms/LowerBitSets/function.ll
> llvm/trunk/test/Transforms/LowerBitSets/nonstring.ll
> Modified:
> llvm/trunk/docs/BitSets.rst
> llvm/trunk/docs/LangRef.rst
> llvm/trunk/include/llvm/Transforms/IPO/LowerBitSets.h
> llvm/trunk/lib/Transforms/IPO/LowerBitSets.cpp
> llvm/trunk/test/Transforms/LowerBitSets/simple.ll
>
> Modified: llvm/trunk/docs/BitSets.rst
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/BitSets.rst?rev=247080&r1=247079&r2=247080&view=diff
> ==============================================================================
> --- llvm/trunk/docs/BitSets.rst (original)
> +++ llvm/trunk/docs/BitSets.rst Tue Sep 8 16:57:45 2015
> @@ -10,17 +10,41 @@ for the type of the class or its derived
>
> To use the mechanism, a client creates a global metadata node named
> ``llvm.bitsets``. Each element is a metadata node with three elements:
> -the first is a metadata string containing an identifier for the bitset,
> -the second is a global variable and the third is a byte offset into the
> -global variable.
> +
> +1. a metadata object representing an identifier for the bitset
> +2. either a global variable or a function
> +3. a byte offset into the global (generally zero for functions)
> +
> +Each bitset must exclusively contain either global variables or functions.
> +
> +.. admonition:: Limitation
> +
> + The current implementation only supports functions as members of bitsets on
> + the x86-32 and x86-64 architectures.
>
> This will cause a link-time optimization pass to generate bitsets from the
> -memory addresses referenced from the elements of the bitset metadata. The pass
> -will lay out the referenced globals consecutively, so their definitions must
> -be available at LTO time. The `GlobalLayoutBuilder`_ class is responsible for
> -laying out the globals efficiently to minimize the sizes of the underlying
> -bitsets. An intrinsic, :ref:`llvm.bitset.test <bitset.test>`, generates code
> -to test whether a given pointer is a member of a bitset.
> +memory addresses referenced from the elements of the bitset metadata. The
> +pass will lay out referenced global variables consecutively, so their
> +definitions must be available at LTO time.
> +
> +A bit set containing functions is transformed into a jump table, which
> +is a block of code consisting of one branch instruction for each of the
> +functions in the bit set that branches to the target function, and redirect
> +any taken function addresses to the corresponding jump table entry. In the
> +object file's symbol table, the jump table entries take the identities of
> +the original functions, so that addresses taken outside the module will pass
> +any verification done inside the module.
> +
> +Jump tables may call external functions, so their definitions need not
> +be available at LTO time. Note that if an externally defined function is a
> +member of a bitset, there is no guarantee that its identity within the module
> +will be the same as its identity outside of the module, as the former will
> +be the jump table entry if a jump table is necessary.
> +
> +The `GlobalLayoutBuilder`_ class is responsible for laying out the globals
> +efficiently to minimize the sizes of the underlying bitsets. An intrinsic,
> +:ref:`llvm.bitset.test <bitset.test>`, generates code to test whether a
> +given pointer is a member of a bitset.
>
> :Example:
>
> @@ -33,13 +57,25 @@ to test whether a given pointer is a mem
> @c = internal global i32 0
> @d = internal global [2 x i32] [i32 0, i32 0]
>
> - !llvm.bitsets = !{!0, !1, !2, !3, !4}
> + define void @e() {
> + ret void
> + }
> +
> + define void @f() {
> + ret void
> + }
> +
> + declare void @g()
> +
> + !llvm.bitsets = !{!0, !1, !2, !3, !4, !5, !6}
>
> !0 = !{!"bitset1", i32* @a, i32 0}
> !1 = !{!"bitset1", i32* @b, i32 0}
> !2 = !{!"bitset2", i32* @b, i32 0}
> !3 = !{!"bitset2", i32* @c, i32 0}
> !4 = !{!"bitset2", i32* @d, i32 4}
> + !5 = !{!"bitset3", void ()* @e, i32 0}
> + !6 = !{!"bitset3", void ()* @g, i32 0}
>
> declare i1 @llvm.bitset.test(i8* %ptr, metadata %bitset) nounwind readnone
>
> @@ -55,6 +91,12 @@ to test whether a given pointer is a mem
> ret i1 %x
> }
>
> + define i1 @baz(void ()* %p) {
> + %pi8 = bitcast void ()* %p to i8*
> + %x = call i1 @llvm.bitset.test(i8* %pi8, metadata !"bitset3")
> + ret i1 %x
> + }
> +
> define void @main() {
> %a1 = call i1 @foo(i32* @a) ; returns 1
> %b1 = call i1 @foo(i32* @b) ; returns 1
> @@ -64,6 +106,9 @@ to test whether a given pointer is a mem
> %c2 = call i1 @bar(i32* @c) ; returns 1
> %d02 = call i1 @bar(i32* getelementptr ([2 x i32]* @d, i32 0, i32 0)) ; returns 0
> %d12 = call i1 @bar(i32* getelementptr ([2 x i32]* @d, i32 0, i32 1)) ; returns 1
> + %e = call i1 @baz(void ()* @e) ; returns 1
> + %f = call i1 @baz(void ()* @f) ; returns 0
> + %g = call i1 @baz(void ()* @g) ; returns 1
> ret void
> }
>
>
> Modified: llvm/trunk/docs/LangRef.rst
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/LangRef.rst?rev=247080&r1=247079&r2=247080&view=diff
> ==============================================================================
> --- llvm/trunk/docs/LangRef.rst (original)
> +++ llvm/trunk/docs/LangRef.rst Tue Sep 8 16:57:45 2015
> @@ -11837,7 +11837,7 @@ Arguments:
> """"""""""
>
> The first argument is a pointer to be tested. The second argument is a
> -metadata string containing the name of a :doc:`bitset <BitSets>`.
> +metadata object representing an identifier for a :doc:`bitset <BitSets>`.
>
> Overview:
> """""""""
>
> Modified: llvm/trunk/include/llvm/Transforms/IPO/LowerBitSets.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/IPO/LowerBitSets.h?rev=247080&r1=247079&r2=247080&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/Transforms/IPO/LowerBitSets.h (original)
> +++ llvm/trunk/include/llvm/Transforms/IPO/LowerBitSets.h Tue Sep 8 16:57:45 2015
> @@ -26,7 +26,7 @@
> namespace llvm {
>
> class DataLayout;
> -class GlobalVariable;
> +class GlobalObject;
> class Value;
> class raw_ostream;
>
> @@ -56,7 +56,7 @@ struct BitSetInfo {
> bool containsGlobalOffset(uint64_t Offset) const;
>
> bool containsValue(const DataLayout &DL,
> - const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout,
> + const DenseMap<GlobalObject *, uint64_t> &GlobalLayout,
> Value *V, uint64_t COffset = 0) const;
>
> void print(raw_ostream &OS) const;
>
> Modified: llvm/trunk/lib/Transforms/IPO/LowerBitSets.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/LowerBitSets.cpp?rev=247080&r1=247079&r2=247080&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/IPO/LowerBitSets.cpp (original)
> +++ llvm/trunk/lib/Transforms/IPO/LowerBitSets.cpp Tue Sep 8 16:57:45 2015
> @@ -19,6 +19,8 @@
> #include "llvm/ADT/Triple.h"
> #include "llvm/IR/Constant.h"
> #include "llvm/IR/Constants.h"
> +#include "llvm/IR/Function.h"
> +#include "llvm/IR/GlobalObject.h"
> #include "llvm/IR/GlobalVariable.h"
> #include "llvm/IR/IRBuilder.h"
> #include "llvm/IR/Instructions.h"
> @@ -61,9 +63,9 @@ bool BitSetInfo::containsGlobalOffset(ui
>
> bool BitSetInfo::containsValue(
> const DataLayout &DL,
> - const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout, Value *V,
> + const DenseMap<GlobalObject *, uint64_t> &GlobalLayout, Value *V,
> uint64_t COffset) const {
> - if (auto GV = dyn_cast<GlobalVariable>(V)) {
> + if (auto GV = dyn_cast<GlobalObject>(V)) {
> auto I = GlobalLayout.find(GV);
> if (I == GlobalLayout.end())
> return false;
> @@ -211,34 +213,48 @@ struct LowerBitSets : public ModulePass
> Module *M;
>
> bool LinkerSubsectionsViaSymbols;
> + Triple::ArchType Arch;
> + Triple::ObjectFormatType ObjectFormat;
> IntegerType *Int1Ty;
> IntegerType *Int8Ty;
> IntegerType *Int32Ty;
> Type *Int32PtrTy;
> IntegerType *Int64Ty;
> - Type *IntPtrTy;
> + IntegerType *IntPtrTy;
>
> // The llvm.bitsets named metadata.
> NamedMDNode *BitSetNM;
>
> - // Mapping from bitset mdstrings to the call sites that test them.
> - DenseMap<MDString *, std::vector<CallInst *>> BitSetTestCallSites;
> + // Mapping from bitset identifiers to the call sites that test them.
> + DenseMap<Metadata *, std::vector<CallInst *>> BitSetTestCallSites;
>
> std::vector<ByteArrayInfo> ByteArrayInfos;
>
> BitSetInfo
> - buildBitSet(MDString *BitSet,
> - const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout);
> + buildBitSet(Metadata *BitSet,
> + const DenseMap<GlobalObject *, uint64_t> &GlobalLayout);
> ByteArrayInfo *createByteArray(BitSetInfo &BSI);
> void allocateByteArrays();
> Value *createBitSetTest(IRBuilder<> &B, BitSetInfo &BSI, ByteArrayInfo *&BAI,
> Value *BitOffset);
> + void lowerBitSetCalls(ArrayRef<Metadata *> BitSets,
> + Constant *CombinedGlobalAddr,
> + const DenseMap<GlobalObject *, uint64_t> &GlobalLayout);
> Value *
> lowerBitSetCall(CallInst *CI, BitSetInfo &BSI, ByteArrayInfo *&BAI,
> - GlobalVariable *CombinedGlobal,
> - const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout);
> - void buildBitSetsFromGlobals(const std::vector<MDString *> &BitSets,
> - const std::vector<GlobalVariable *> &Globals);
> + Constant *CombinedGlobal,
> + const DenseMap<GlobalObject *, uint64_t> &GlobalLayout);
> + void buildBitSetsFromGlobalVariables(ArrayRef<Metadata *> BitSets,
> + ArrayRef<GlobalVariable *> Globals);
> + unsigned getJumpTableEntrySize();
> + Type *getJumpTableEntryType();
> + Constant *createJumpTableEntry(GlobalObject *Src, Function *Dest,
> + unsigned Distance);
> + void verifyBitSetMDNode(MDNode *Op);
> + void buildBitSetsFromFunctions(ArrayRef<Metadata *> BitSets,
> + ArrayRef<Function *> Functions);
> + void buildBitSetsFromDisjointSet(ArrayRef<Metadata *> BitSets,
> + ArrayRef<GlobalObject *> Globals);
> bool buildBitSets();
> bool eraseBitSetMetadata();
>
> @@ -262,6 +278,8 @@ bool LowerBitSets::doInitialization(Modu
>
> Triple TargetTriple(M->getTargetTriple());
> LinkerSubsectionsViaSymbols = TargetTriple.isMacOSX();
> + Arch = TargetTriple.getArch();
> + ObjectFormat = TargetTriple.getObjectFormat();
>
> Int1Ty = Type::getInt1Ty(M->getContext());
> Int8Ty = Type::getInt8Ty(M->getContext());
> @@ -280,8 +298,8 @@ bool LowerBitSets::doInitialization(Modu
> /// Build a bit set for BitSet using the object layouts in
> /// GlobalLayout.
> BitSetInfo LowerBitSets::buildBitSet(
> - MDString *BitSet,
> - const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout) {
> + Metadata *BitSet,
> + const DenseMap<GlobalObject *, uint64_t> &GlobalLayout) {
> BitSetBuilder BSB;
>
> // Compute the byte offset of each element of this bitset.
> @@ -289,8 +307,11 @@ BitSetInfo LowerBitSets::buildBitSet(
> for (MDNode *Op : BitSetNM->operands()) {
> if (Op->getOperand(0) != BitSet || !Op->getOperand(1))
> continue;
> - auto OpGlobal = dyn_cast<GlobalVariable>(
> - cast<ConstantAsMetadata>(Op->getOperand(1))->getValue());
> + Constant *OpConst =
> + cast<ConstantAsMetadata>(Op->getOperand(1))->getValue();
> + if (auto GA = dyn_cast<GlobalAlias>(OpConst))
> + OpConst = GA->getAliasee();
> + auto OpGlobal = dyn_cast<GlobalObject>(OpConst);
> if (!OpGlobal)
> continue;
> uint64_t Offset =
> @@ -439,17 +460,16 @@ Value *LowerBitSets::createBitSetTest(IR
> /// replace the call with.
> Value *LowerBitSets::lowerBitSetCall(
> CallInst *CI, BitSetInfo &BSI, ByteArrayInfo *&BAI,
> - GlobalVariable *CombinedGlobal,
> - const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout) {
> + Constant *CombinedGlobalIntAddr,
> + const DenseMap<GlobalObject *, uint64_t> &GlobalLayout) {
> Value *Ptr = CI->getArgOperand(0);
> const DataLayout &DL = M->getDataLayout();
>
> if (BSI.containsValue(DL, GlobalLayout, Ptr))
> - return ConstantInt::getTrue(CombinedGlobal->getParent()->getContext());
> + return ConstantInt::getTrue(M->getContext());
>
> - Constant *GlobalAsInt = ConstantExpr::getPtrToInt(CombinedGlobal, IntPtrTy);
> Constant *OffsetedGlobalAsInt = ConstantExpr::getAdd(
> - GlobalAsInt, ConstantInt::get(IntPtrTy, BSI.ByteOffset));
> + CombinedGlobalIntAddr, ConstantInt::get(IntPtrTy, BSI.ByteOffset));
>
> BasicBlock *InitialBB = CI->getParent();
>
> @@ -508,18 +528,19 @@ Value *LowerBitSets::lowerBitSetCall(
>
> /// Given a disjoint set of bitsets and globals, layout the globals, build the
> /// bit sets and lower the llvm.bitset.test calls.
> -void LowerBitSets::buildBitSetsFromGlobals(
> - const std::vector<MDString *> &BitSets,
> - const std::vector<GlobalVariable *> &Globals) {
> +void LowerBitSets::buildBitSetsFromGlobalVariables(
> + ArrayRef<Metadata *> BitSets, ArrayRef<GlobalVariable *> Globals) {
> // Build a new global with the combined contents of the referenced globals.
> + // This global is a struct whose even-indexed elements contain the original
> + // contents of the referenced globals and whose odd-indexed elements contain
> + // any padding required to align the next element to the next power of 2.
> std::vector<Constant *> GlobalInits;
> const DataLayout &DL = M->getDataLayout();
> for (GlobalVariable *G : Globals) {
> GlobalInits.push_back(G->getInitializer());
> uint64_t InitSize = DL.getTypeAllocSize(G->getInitializer()->getType());
>
> - // Compute the amount of padding required to align the next element to the
> - // next power of 2.
> + // Compute the amount of padding required.
> uint64_t Padding = NextPowerOf2(InitSize - 1) - InitSize;
>
> // Cap at 128 was found experimentally to have a good data/instruction
> @@ -541,30 +562,12 @@ void LowerBitSets::buildBitSetsFromGloba
> DL.getStructLayout(cast<StructType>(NewInit->getType()));
>
> // Compute the offsets of the original globals within the new global.
> - DenseMap<GlobalVariable *, uint64_t> GlobalLayout;
> + DenseMap<GlobalObject *, uint64_t> GlobalLayout;
> for (unsigned I = 0; I != Globals.size(); ++I)
> // Multiply by 2 to account for padding elements.
> GlobalLayout[Globals[I]] = CombinedGlobalLayout->getElementOffset(I * 2);
>
> - // For each bitset in this disjoint set...
> - for (MDString *BS : BitSets) {
> - // Build the bitset.
> - BitSetInfo BSI = buildBitSet(BS, GlobalLayout);
> - DEBUG({
> - dbgs() << BS->getString() << ": ";
> - BSI.print(dbgs());
> - });
> -
> - ByteArrayInfo *BAI = 0;
> -
> - // Lower each call to llvm.bitset.test for this bitset.
> - for (CallInst *CI : BitSetTestCallSites[BS]) {
> - ++NumBitSetCallsLowered;
> - Value *Lowered = lowerBitSetCall(CI, BSI, BAI, CombinedGlobal, GlobalLayout);
> - CI->replaceAllUsesWith(Lowered);
> - CI->eraseFromParent();
> - }
> - }
> + lowerBitSetCalls(BitSets, CombinedGlobal, GlobalLayout);
>
> // Build aliases pointing to offsets into the combined global for each
> // global from which we built the combined global, and replace references
> @@ -581,6 +584,7 @@ void LowerBitSets::buildBitSetsFromGloba
> GlobalAlias *GAlias =
> GlobalAlias::create(Globals[I]->getType(), Globals[I]->getLinkage(),
> "", CombinedGlobalElemPtr, M);
> + GAlias->setVisibility(Globals[I]->getVisibility());
> GAlias->takeName(Globals[I]);
> Globals[I]->replaceAllUsesWith(GAlias);
> }
> @@ -588,6 +592,330 @@ void LowerBitSets::buildBitSetsFromGloba
> }
> }
>
> +void LowerBitSets::lowerBitSetCalls(
> + ArrayRef<Metadata *> BitSets, Constant *CombinedGlobalAddr,
> + const DenseMap<GlobalObject *, uint64_t> &GlobalLayout) {
> + Constant *CombinedGlobalIntAddr =
> + ConstantExpr::getPtrToInt(CombinedGlobalAddr, IntPtrTy);
> +
> + // For each bitset in this disjoint set...
> + for (Metadata *BS : BitSets) {
> + // Build the bitset.
> + BitSetInfo BSI = buildBitSet(BS, GlobalLayout);
> + DEBUG({
> + if (auto BSS = dyn_cast<MDString>(BS))
> + dbgs() << BSS->getString() << ": ";
> + else
> + dbgs() << "<unnamed>: ";
> + BSI.print(dbgs());
> + });
> +
> + ByteArrayInfo *BAI = 0;
> +
> + // Lower each call to llvm.bitset.test for this bitset.
> + for (CallInst *CI : BitSetTestCallSites[BS]) {
> + ++NumBitSetCallsLowered;
> + Value *Lowered =
> + lowerBitSetCall(CI, BSI, BAI, CombinedGlobalIntAddr, GlobalLayout);
> + CI->replaceAllUsesWith(Lowered);
> + CI->eraseFromParent();
> + }
> + }
> +}
> +
> +void LowerBitSets::verifyBitSetMDNode(MDNode *Op) {
> + if (Op->getNumOperands() != 3)
> + report_fatal_error(
> + "All operands of llvm.bitsets metadata must have 3 elements");
> + if (!Op->getOperand(1))
> + return;
> +
> + auto OpConstMD = dyn_cast<ConstantAsMetadata>(Op->getOperand(1));
> + if (!OpConstMD)
> + report_fatal_error("Bit set element must be a constant");
> + auto OpGlobal = dyn_cast<GlobalObject>(OpConstMD->getValue());
> + if (!OpGlobal)
> + return;
> +
> + if (OpGlobal->isThreadLocal())
> + report_fatal_error("Bit set element may not be thread-local");
> + if (OpGlobal->hasSection())
> + report_fatal_error("Bit set element may not have an explicit section");
> +
> + if (isa<GlobalVariable>(OpGlobal) && OpGlobal->isDeclarationForLinker())
> + report_fatal_error("Bit set global var element must be a definition");
> +
> + auto OffsetConstMD = dyn_cast<ConstantAsMetadata>(Op->getOperand(2));
> + if (!OffsetConstMD)
> + report_fatal_error("Bit set element offset must be a constant");
> + auto OffsetInt = dyn_cast<ConstantInt>(OffsetConstMD->getValue());
> + if (!OffsetInt)
> + report_fatal_error("Bit set element offset must be an integer constant");
> +}
> +
> +static const unsigned kX86JumpTableEntrySize = 8;
> +
> +unsigned LowerBitSets::getJumpTableEntrySize() {
> + if (Arch != Triple::x86 && Arch != Triple::x86_64)
> + report_fatal_error("Unsupported architecture for jump tables");
> +
> + return kX86JumpTableEntrySize;
> +}
> +
> +// Create a constant representing a jump table entry for the target. This
> +// consists of an instruction sequence containing a relative branch to Dest. The
> +// constant will be laid out at address Src+(Len*Distance) where Len is the
> +// target-specific jump table entry size.
> +Constant *LowerBitSets::createJumpTableEntry(GlobalObject *Src, Function *Dest,
> + unsigned Distance) {
> + if (Arch != Triple::x86 && Arch != Triple::x86_64)
> + report_fatal_error("Unsupported architecture for jump tables");
> +
> + const unsigned kJmpPCRel32Code = 0xe9;
> + const unsigned kInt3Code = 0xcc;
> +
> + ConstantInt *Jmp = ConstantInt::get(Int8Ty, kJmpPCRel32Code);
> +
> + // Build a constant representing the displacement between the constant's
> + // address and Dest. This will resolve to a PC32 relocation referring to Dest.
> + Constant *DestInt = ConstantExpr::getPtrToInt(Dest, IntPtrTy);
> + Constant *SrcInt = ConstantExpr::getPtrToInt(Src, IntPtrTy);
> + Constant *Disp = ConstantExpr::getSub(DestInt, SrcInt);
> + ConstantInt *DispOffset =
> + ConstantInt::get(IntPtrTy, Distance * kX86JumpTableEntrySize + 5);
> + Constant *OffsetedDisp = ConstantExpr::getSub(Disp, DispOffset);
> + OffsetedDisp = ConstantExpr::getTrunc(OffsetedDisp, Int32Ty);
> +
> + ConstantInt *Int3 = ConstantInt::get(Int8Ty, kInt3Code);
> +
> + Constant *Fields[] = {
> + Jmp, OffsetedDisp, Int3, Int3, Int3,
> + };
> + return ConstantStruct::getAnon(Fields, /*Packed=*/true);
> +}
> +
> +Type *LowerBitSets::getJumpTableEntryType() {
> + if (Arch != Triple::x86 && Arch != Triple::x86_64)
> + report_fatal_error("Unsupported architecture for jump tables");
> +
> + return StructType::get(M->getContext(),
> + {Int8Ty, Int32Ty, Int8Ty, Int8Ty, Int8Ty},
> + /*Packed=*/true);
> +}
> +
> +/// Given a disjoint set of bitsets and functions, build a jump table for the
> +/// functions, build the bit sets and lower the llvm.bitset.test calls.
> +void LowerBitSets::buildBitSetsFromFunctions(ArrayRef<Metadata *> BitSets,
> + ArrayRef<Function *> Functions) {
> + // Unlike the global bitset builder, the function bitset builder cannot
> + // re-arrange functions in a particular order and base its calculations on the
> + // layout of the functions' entry points, as we have no idea how large a
> + // particular function will end up being (the size could even depend on what
> + // this pass does!) Instead, we build a jump table, which is a block of code
> + // consisting of one branch instruction for each of the functions in the bit
> + // set that branches to the target function, and redirect any taken function
> + // addresses to the corresponding jump table entry. In the object file's
> + // symbol table, the symbols for the target functions also refer to the jump
> + // table entries, so that addresses taken outside the module will pass any
> + // verification done inside the module.
> + //
> + // In more concrete terms, suppose we have three functions f, g, h which are
> + // members of a single bitset, and a function foo that returns their
> + // addresses:
> + //
> + // f:
> + // mov 0, %eax
> + // ret
> + //
> + // g:
> + // mov 1, %eax
> + // ret
> + //
> + // h:
> + // mov 2, %eax
> + // ret
> + //
> + // foo:
> + // mov f, %eax
> + // mov g, %edx
> + // mov h, %ecx
> + // ret
> + //
> + // To create a jump table for these functions, we instruct the LLVM code
> + // generator to output a jump table in the .text section. This is done by
> + // representing the instructions in the jump table as an LLVM constant and
> + // placing them in a global variable in the .text section. The end result will
> + // (conceptually) look like this:
> + //
> + // f:
> + // jmp .Ltmp0 ; 5 bytes
> + // int3 ; 1 byte
> + // int3 ; 1 byte
> + // int3 ; 1 byte
> + //
> + // g:
> + // jmp .Ltmp1 ; 5 bytes
> + // int3 ; 1 byte
> + // int3 ; 1 byte
> + // int3 ; 1 byte
> + //
> + // h:
> + // jmp .Ltmp2 ; 5 bytes
> + // int3 ; 1 byte
> + // int3 ; 1 byte
> + // int3 ; 1 byte
> + //
> + // .Ltmp0:
> + // mov 0, %eax
> + // ret
> + //
> + // .Ltmp1:
> + // mov 1, %eax
> + // ret
> + //
> + // .Ltmp2:
> + // mov 2, %eax
> + // ret
> + //
> + // foo:
> + // mov f, %eax
> + // mov g, %edx
> + // mov h, %ecx
> + // ret
> + //
> + // Because the addresses of f, g, h are evenly spaced at a power of 2, in the
> + // normal case the check can be carried out using the same kind of simple
> + // arithmetic that we normally use for globals.
> +
> + assert(!Functions.empty());
> +
> + // Build a simple layout based on the regular layout of jump tables.
> + DenseMap<GlobalObject *, uint64_t> GlobalLayout;
> + unsigned EntrySize = getJumpTableEntrySize();
> + for (unsigned I = 0; I != Functions.size(); ++I)
> + GlobalLayout[Functions[I]] = I * EntrySize;
> +
> + // Create a constant to hold the jump table.
> + ArrayType *JumpTableType =
> + ArrayType::get(getJumpTableEntryType(), Functions.size());
> + auto JumpTable = new GlobalVariable(*M, JumpTableType,
> + /*isConstant=*/true,
> + GlobalValue::PrivateLinkage, nullptr);
> + JumpTable->setSection(ObjectFormat == Triple::MachO
> + ? "__TEXT,__text,regular,pure_instructions"
> + : ".text");
> + lowerBitSetCalls(BitSets, JumpTable, GlobalLayout);
> +
> + // Build aliases pointing to offsets into the jump table, and replace
> + // references to the original functions with references to the aliases.
> + for (unsigned I = 0; I != Functions.size(); ++I) {
> + Constant *CombinedGlobalElemPtr = ConstantExpr::getBitCast(
> + ConstantExpr::getGetElementPtr(
> + JumpTableType, JumpTable,
> + ArrayRef<Constant *>{ConstantInt::get(IntPtrTy, 0),
> + ConstantInt::get(IntPtrTy, I)}),
> + Functions[I]->getType());
> + if (LinkerSubsectionsViaSymbols || Functions[I]->isDeclarationForLinker()) {
> + Functions[I]->replaceAllUsesWith(CombinedGlobalElemPtr);
> + } else {
> + GlobalAlias *GAlias = GlobalAlias::create(Functions[I]->getType(),
> + Functions[I]->getLinkage(), "",
> + CombinedGlobalElemPtr, M);
> + GAlias->setVisibility(Functions[I]->getVisibility());
> + GAlias->takeName(Functions[I]);
> + Functions[I]->replaceAllUsesWith(GAlias);
> + }
> + if (!Functions[I]->isDeclarationForLinker())
> + Functions[I]->setLinkage(GlobalValue::PrivateLinkage);
> + }
> +
> + // Build and set the jump table's initializer.
> + std::vector<Constant *> JumpTableEntries;
> + for (unsigned I = 0; I != Functions.size(); ++I)
> + JumpTableEntries.push_back(
> + createJumpTableEntry(JumpTable, Functions[I], I));
> + JumpTable->setInitializer(
> + ConstantArray::get(JumpTableType, JumpTableEntries));
> +}
> +
> +void LowerBitSets::buildBitSetsFromDisjointSet(
> + ArrayRef<Metadata *> BitSets, ArrayRef<GlobalObject *> Globals) {
> + llvm::DenseMap<Metadata *, uint64_t> BitSetIndices;
> + llvm::DenseMap<GlobalObject *, uint64_t> GlobalIndices;
> + for (auto B : BitSets)
> + BitSetIndices[B] = BitSetIndices.size();
> + for (auto G : Globals)
> + GlobalIndices[G] = GlobalIndices.size();
> +
> + // For each bitset, build a set of indices that refer to globals referenced by
> + // the bitset.
> + std::vector<std::set<uint64_t>> BitSetMembers(BitSets.size());
> + if (BitSetNM) {
> + for (MDNode *Op : BitSetNM->operands()) {
> + // Op = { bitset name, global, offset }
> + if (!Op->getOperand(1))
> + continue;
> + auto I = BitSetIndices.find(Op->getOperand(0));
> + if (I == BitSetIndices.end())
> + continue;
> +
> + auto OpGlobal = dyn_cast<GlobalObject>(
> + cast<ConstantAsMetadata>(Op->getOperand(1))->getValue());
> + if (!OpGlobal)
> + continue;
> + BitSetMembers[I->second].insert(GlobalIndices[OpGlobal]);
> + }
> + }
> +
> + // Order the sets of indices by size. The GlobalLayoutBuilder works best
> + // when given small index sets first.
> + std::stable_sort(
> + BitSetMembers.begin(), BitSetMembers.end(),
> + [](const std::set<uint64_t> &O1, const std::set<uint64_t> &O2) {
> + return O1.size() < O2.size();
> + });
> +
> + // Create a GlobalLayoutBuilder and provide it with index sets as layout
> + // fragments. The GlobalLayoutBuilder tries to lay out members of fragments as
> + // close together as possible.
> + GlobalLayoutBuilder GLB(Globals.size());
> + for (auto &&MemSet : BitSetMembers)
> + GLB.addFragment(MemSet);
> +
> + // Build the bitsets from this disjoint set.
> + if (Globals.empty() || isa<GlobalVariable>(Globals[0])) {
> + // Build a vector of global variables with the computed layout.
> + std::vector<GlobalVariable *> OrderedGVs(Globals.size());
> + auto OGI = OrderedGVs.begin();
> + for (auto &&F : GLB.Fragments) {
> + for (auto &&Offset : F) {
> + auto GV = dyn_cast<GlobalVariable>(Globals[Offset]);
> + if (!GV)
> + report_fatal_error(
> + "Bit set may not contain both global variables and functions");
> + *OGI++ = GV;
> + }
> + }
> +
> + buildBitSetsFromGlobalVariables(BitSets, OrderedGVs);
> + } else {
> + // Build a vector of functions with the computed layout.
> + std::vector<Function *> OrderedFns(Globals.size());
> + auto OFI = OrderedFns.begin();
> + for (auto &&F : GLB.Fragments) {
> + for (auto &&Offset : F) {
> + auto Fn = dyn_cast<Function>(Globals[Offset]);
> + if (!Fn)
> + report_fatal_error(
> + "Bit set may not contain both global variables and functions");
> + *OFI++ = Fn;
> + }
> + }
> +
> + buildBitSetsFromFunctions(BitSets, OrderedFns);
> + }
> +}
> +
> /// Lower all bit sets in this module.
> bool LowerBitSets::buildBitSets() {
> Function *BitSetTestFunc =
> @@ -598,24 +926,36 @@ bool LowerBitSets::buildBitSets() {
> // Equivalence class set containing bitsets and the globals they reference.
> // This is used to partition the set of bitsets in the module into disjoint
> // sets.
> - typedef EquivalenceClasses<PointerUnion<GlobalVariable *, MDString *>>
> + typedef EquivalenceClasses<PointerUnion<GlobalObject *, Metadata *>>
> GlobalClassesTy;
> GlobalClassesTy GlobalClasses;
>
> + // Verify the bitset metadata and build a mapping from bitset identifiers to
> + // their last observed index in BitSetNM. This will used later to
> + // deterministically order the list of bitset identifiers.
> + llvm::DenseMap<Metadata *, unsigned> BitSetIdIndices;
> + if (BitSetNM) {
> + for (unsigned I = 0, E = BitSetNM->getNumOperands(); I != E; ++I) {
> + MDNode *Op = BitSetNM->getOperand(I);
> + verifyBitSetMDNode(Op);
> + BitSetIdIndices[Op] = I;
> + }
> + }
> +
> for (const Use &U : BitSetTestFunc->uses()) {
> auto CI = cast<CallInst>(U.getUser());
>
> auto BitSetMDVal = dyn_cast<MetadataAsValue>(CI->getArgOperand(1));
> - if (!BitSetMDVal || !isa<MDString>(BitSetMDVal->getMetadata()))
> + if (!BitSetMDVal)
> report_fatal_error(
> - "Second argument of llvm.bitset.test must be metadata string");
> - auto BitSet = cast<MDString>(BitSetMDVal->getMetadata());
> + "Second argument of llvm.bitset.test must be metadata");
> + auto BitSet = BitSetMDVal->getMetadata();
>
> // Add the call site to the list of call sites for this bit set. We also use
> // BitSetTestCallSites to keep track of whether we have seen this bit set
> // before. If we have, we don't need to re-add the referenced globals to the
> // equivalence class.
> - std::pair<DenseMap<MDString *, std::vector<CallInst *>>::iterator,
> + std::pair<DenseMap<Metadata *, std::vector<CallInst *>>::iterator,
> bool> Ins =
> BitSetTestCallSites.insert(
> std::make_pair(BitSet, std::vector<CallInst *>()));
> @@ -630,31 +970,16 @@ bool LowerBitSets::buildBitSets() {
> if (!BitSetNM)
> continue;
>
> - // Verify the bitset metadata and add the referenced globals to the bitset's
> - // equivalence class.
> + // Add the referenced globals to the bitset's equivalence class.
> for (MDNode *Op : BitSetNM->operands()) {
> - if (Op->getNumOperands() != 3)
> - report_fatal_error(
> - "All operands of llvm.bitsets metadata must have 3 elements");
> -
> if (Op->getOperand(0) != BitSet || !Op->getOperand(1))
> continue;
>
> - auto OpConstMD = dyn_cast<ConstantAsMetadata>(Op->getOperand(1));
> - if (!OpConstMD)
> - report_fatal_error("Bit set element must be a constant");
> - auto OpGlobal = dyn_cast<GlobalVariable>(OpConstMD->getValue());
> + auto OpGlobal = dyn_cast<GlobalObject>(
> + cast<ConstantAsMetadata>(Op->getOperand(1))->getValue());
> if (!OpGlobal)
> continue;
>
> - auto OffsetConstMD = dyn_cast<ConstantAsMetadata>(Op->getOperand(2));
> - if (!OffsetConstMD)
> - report_fatal_error("Bit set element offset must be a constant");
> - auto OffsetInt = dyn_cast<ConstantInt>(OffsetConstMD->getValue());
> - if (!OffsetInt)
> - report_fatal_error(
> - "Bit set element offset must be an integer constant");
> -
> CurSet = GlobalClasses.unionSets(
> CurSet, GlobalClasses.findLeader(GlobalClasses.insert(OpGlobal)));
> }
> @@ -671,71 +996,25 @@ bool LowerBitSets::buildBitSets() {
>
> ++NumBitSetDisjointSets;
>
> - // Build the list of bitsets and referenced globals in this disjoint set.
> - std::vector<MDString *> BitSets;
> - std::vector<GlobalVariable *> Globals;
> - llvm::DenseMap<MDString *, uint64_t> BitSetIndices;
> - llvm::DenseMap<GlobalVariable *, uint64_t> GlobalIndices;
> + // Build the list of bitsets in this disjoint set.
> + std::vector<Metadata *> BitSets;
> + std::vector<GlobalObject *> Globals;
> for (GlobalClassesTy::member_iterator MI = GlobalClasses.member_begin(I);
> MI != GlobalClasses.member_end(); ++MI) {
> - if ((*MI).is<MDString *>()) {
> - BitSetIndices[MI->get<MDString *>()] = BitSets.size();
> - BitSets.push_back(MI->get<MDString *>());
> - } else {
> - GlobalIndices[MI->get<GlobalVariable *>()] = Globals.size();
> - Globals.push_back(MI->get<GlobalVariable *>());
> - }
> - }
> -
> - // For each bitset, build a set of indices that refer to globals referenced
> - // by the bitset.
> - std::vector<std::set<uint64_t>> BitSetMembers(BitSets.size());
> - if (BitSetNM) {
> - for (MDNode *Op : BitSetNM->operands()) {
> - // Op = { bitset name, global, offset }
> - if (!Op->getOperand(1))
> - continue;
> - auto I = BitSetIndices.find(cast<MDString>(Op->getOperand(0)));
> - if (I == BitSetIndices.end())
> - continue;
> -
> - auto OpGlobal = dyn_cast<GlobalVariable>(
> - cast<ConstantAsMetadata>(Op->getOperand(1))->getValue());
> - if (!OpGlobal)
> - continue;
> - BitSetMembers[I->second].insert(GlobalIndices[OpGlobal]);
> - }
> + if ((*MI).is<Metadata *>())
> + BitSets.push_back(MI->get<Metadata *>());
> + else
> + Globals.push_back(MI->get<GlobalObject *>());
> }
>
> - // Order the sets of indices by size. The GlobalLayoutBuilder works best
> - // when given small index sets first.
> - std::stable_sort(
> - BitSetMembers.begin(), BitSetMembers.end(),
> - [](const std::set<uint64_t> &O1, const std::set<uint64_t> &O2) {
> - return O1.size() < O2.size();
> - });
> -
> - // Create a GlobalLayoutBuilder and provide it with index sets as layout
> - // fragments. The GlobalLayoutBuilder tries to lay out members of fragments
> - // as close together as possible.
> - GlobalLayoutBuilder GLB(Globals.size());
> - for (auto &&MemSet : BitSetMembers)
> - GLB.addFragment(MemSet);
> -
> - // Build a vector of globals with the computed layout.
> - std::vector<GlobalVariable *> OrderedGlobals(Globals.size());
> - auto OGI = OrderedGlobals.begin();
> - for (auto &&F : GLB.Fragments)
> - for (auto &&Offset : F)
> - *OGI++ = Globals[Offset];
> -
> - // Order bitsets by name for determinism.
> - std::sort(BitSets.begin(), BitSets.end(), [](MDString *S1, MDString *S2) {
> - return S1->getString() < S2->getString();
> + // Order bitsets by BitSetNM index for determinism. This ordering is stable
> + // as there is a one-to-one mapping between metadata and indices.
> + std::sort(BitSets.begin(), BitSets.end(), [&](Metadata *M1, Metadata *M2) {
> + return BitSetIdIndices[M1] < BitSetIdIndices[M2];
> });
>
> - // Build the bitsets from this disjoint set.
> - buildBitSetsFromGlobals(BitSets, OrderedGlobals);
> + // Lower the bitsets in this disjoint set.
> + buildBitSetsFromDisjointSet(BitSets, Globals);
> }
>
> allocateByteArrays();
>
> Added: llvm/trunk/test/Transforms/LowerBitSets/function-ext.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LowerBitSets/function-ext.ll?rev=247080&view=auto
> ==============================================================================
> --- llvm/trunk/test/Transforms/LowerBitSets/function-ext.ll (added)
> +++ llvm/trunk/test/Transforms/LowerBitSets/function-ext.ll Tue Sep 8 16:57:45 2015
> @@ -0,0 +1,22 @@
> +; RUN: opt -S -lowerbitsets < %s | FileCheck %s
> +
> +; Tests that we correctly handle external references, including the case where
> +; all functions in a bitset are external references.
> +
> +target triple = "x86_64-unknown-linux-gnu"
> +
> +declare void @foo()
> +
> +; CHECK: @[[JT:.*]] = private constant [1 x <{ i8, i32, i8, i8, i8 }>] [<{ i8, i32, i8, i8, i8 }> <{ i8 -23, i32 trunc (i64 sub (i64 sub (i64 ptrtoint (void ()* @foo to i64), i64 ptrtoint ([1 x <{ i8, i32, i8, i8, i8 }>]* @[[JT]] to i64)), i64 5) to i32), i8 -52, i8 -52, i8 -52 }>], section ".text"
> +
> +define i1 @bar(i8* %ptr) {
> + ; CHECK: icmp eq i64 {{.*}}, ptrtoint ([1 x <{ i8, i32, i8, i8, i8 }>]* @[[JT]] to i64)
> + %p = call i1 @llvm.bitset.test(i8* %ptr, metadata !"void")
> + ret i1 %p
> +}
> +
> +declare i1 @llvm.bitset.test(i8* %ptr, metadata %bitset) nounwind readnone
> +
> +!0 = !{!"void", void ()* @foo, i64 0}
> +
> +!llvm.bitsets = !{!0}
>
> Added: llvm/trunk/test/Transforms/LowerBitSets/function.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LowerBitSets/function.ll?rev=247080&view=auto
> ==============================================================================
> --- llvm/trunk/test/Transforms/LowerBitSets/function.ll (added)
> +++ llvm/trunk/test/Transforms/LowerBitSets/function.ll Tue Sep 8 16:57:45 2015
> @@ -0,0 +1,35 @@
> +; RUN: opt -S -lowerbitsets < %s | FileCheck %s
> +
> +; Tests that we correctly create a jump table for bitsets containing 2 or more
> +; functions.
> +
> +target triple = "x86_64-unknown-linux-gnu"
> +target datalayout = "e-p:64:64"
> +
> +; CHECK: @[[JT:.*]] = private constant [2 x <{ i8, i32, i8, i8, i8 }>] [<{ i8, i32, i8, i8, i8 }> <{ i8 -23, i32 trunc (i64 sub (i64 sub (i64 ptrtoint (void ()* @[[FNAME:.*]] to i64), i64 ptrtoint ([2 x <{ i8, i32, i8, i8, i8 }>]* @[[JT]] to i64)), i64 5) to i32), i8 -52, i8 -52, i8 -52 }>, <{ i8, i32, i8, i8, i8 }> <{ i8 -23, i32 trunc (i64 sub (i64 sub (i64 ptrtoint (void ()* @[[GNAME:.*]] to i64), i64 ptrtoint ([2 x <{ i8, i32, i8, i8, i8 }>]* @[[JT]] to i64)), i64 13) to i32), i8 -52, i8 -52, i8 -52 }>], section ".text"
> +
> +; CHECK: @f = alias bitcast ([2 x <{ i8, i32, i8, i8, i8 }>]* @[[JT]] to void ()*)
> +; CHECK: @g = alias bitcast (<{ i8, i32, i8, i8, i8 }>* getelementptr inbounds ([2 x <{ i8, i32, i8, i8, i8 }>], [2 x <{ i8, i32, i8, i8, i8 }>]* @[[JT]], i64 0, i64 1) to void ()*)
> +
> +; CHECK: define private void @[[FNAME]]() {
> +define void @f() {
> + ret void
> +}
> +
> +; CHECK: define private void @[[GNAME]]() {
> +define void @g() {
> + ret void
> +}
> +
> +!0 = !{!"bitset1", void ()* @f, i32 0}
> +!1 = !{!"bitset1", void ()* @g, i32 0}
> +
> +!llvm.bitsets = !{ !0, !1 }
> +
> +declare i1 @llvm.bitset.test(i8* %ptr, metadata %bitset) nounwind readnone
> +
> +define i1 @foo(i8* %p) {
> + ; CHECK: sub i64 {{.*}}, ptrtoint ([2 x <{ i8, i32, i8, i8, i8 }>]* @[[JT]] to i64)
> + %x = call i1 @llvm.bitset.test(i8* %p, metadata !"bitset1")
> + ret i1 %x
> +}
>
> Added: llvm/trunk/test/Transforms/LowerBitSets/nonstring.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LowerBitSets/nonstring.ll?rev=247080&view=auto
> ==============================================================================
> --- llvm/trunk/test/Transforms/LowerBitSets/nonstring.ll (added)
> +++ llvm/trunk/test/Transforms/LowerBitSets/nonstring.ll Tue Sep 8 16:57:45 2015
> @@ -0,0 +1,34 @@
> +; RUN: opt -S -lowerbitsets < %s | FileCheck %s
> +
> +; Tests that non-string metadata nodes may be used as bitset identifiers.
> +
> +target datalayout = "e-p:32:32"
> +
> +; CHECK: @[[BNAME:.*]] = private constant { [2 x i32] }
> +; CHECK: @[[ANAME:.*]] = private constant { i32 }
> +
> + at a = constant i32 1
> + at b = constant [2 x i32] [i32 2, i32 3]
> +
> +!0 = !{!2, i32* @a, i32 0}
> +!1 = !{!3, [2 x i32]* @b, i32 0}
> +!2 = distinct !{}
> +!3 = distinct !{}
> +
> +!llvm.bitsets = !{ !0, !1 }
> +
> +declare i1 @llvm.bitset.test(i8* %ptr, metadata %bitset) nounwind readnone
> +
> +; CHECK-LABEL: @foo
> +define i1 @foo(i8* %p) {
> + ; CHECK: icmp eq i32 {{.*}}, ptrtoint ({ i32 }* @[[ANAME]] to i32)
> + %x = call i1 @llvm.bitset.test(i8* %p, metadata !2)
> + ret i1 %x
> +}
> +
> +; CHECK-LABEL: @bar
> +define i1 @bar(i8* %p) {
> + ; CHECK: icmp eq i32 {{.*}}, ptrtoint ({ [2 x i32] }* @[[BNAME]] to i32)
> + %x = call i1 @llvm.bitset.test(i8* %p, metadata !3)
> + ret i1 %x
> +}
>
> Modified: llvm/trunk/test/Transforms/LowerBitSets/simple.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LowerBitSets/simple.ll?rev=247080&r1=247079&r2=247080&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/LowerBitSets/simple.ll (original)
> +++ llvm/trunk/test/Transforms/LowerBitSets/simple.ll Tue Sep 8 16:57:45 2015
> @@ -6,8 +6,8 @@ target datalayout = "e-p:32:32"
>
> ; CHECK: [[G:@[^ ]*]] = private constant { i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] } { i32 1, [0 x i8] zeroinitializer, [63 x i32] zeroinitializer, [4 x i8] zeroinitializer, i32 3, [0 x i8] zeroinitializer, [2 x i32] [i32 4, i32 5] }
> @a = constant i32 1
> - at b = constant [63 x i32] zeroinitializer
> - at c = constant i32 3
> + at b = hidden constant [63 x i32] zeroinitializer
> + at c = protected constant i32 3
> @d = constant [2 x i32] [i32 4, i32 5]
>
> ; CHECK: [[BA:@[^ ]*]] = private constant [68 x i8] c"\03\01\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\02\00\01"
> @@ -43,8 +43,8 @@ target datalayout = "e-p:32:32"
> ; CHECK: @bits_use.{{[0-9]*}} = private alias i8* @bits{{[0-9]*}}
>
> ; CHECK: @a = alias getelementptr inbounds ({ i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }, { i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }* [[G]], i32 0, i32 0)
> -; CHECK: @b = alias getelementptr inbounds ({ i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }, { i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }* [[G]], i32 0, i32 2)
> -; CHECK: @c = alias getelementptr inbounds ({ i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }, { i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }* [[G]], i32 0, i32 4)
> +; CHECK: @b = hidden alias getelementptr inbounds ({ i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }, { i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }* [[G]], i32 0, i32 2)
> +; CHECK: @c = protected alias getelementptr inbounds ({ i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }, { i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }* [[G]], i32 0, i32 4)
> ; CHECK: @d = alias getelementptr inbounds ({ i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }, { i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }* [[G]], i32 0, i32 6)
>
> ; CHECK-DARWIN: @aptr = constant i32* getelementptr inbounds ({ i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }, { i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }* [[G:@[^ ]*]], i32 0, i32 0)
>
>
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