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Commit921c6db

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[llvm] Introduce callee_type metadata
Introduce `callee_type` metadata which will be attached to the indirectcall instructions.The `callee_type` metadata will be used to generate `.callgraph` sectiondescribed in this RFC:https://lists.llvm.org/pipermail/llvm-dev/2021-July/151739.htmlReviewers: morehouse, petrhosek, nikic, ilovepiReviewed By: nikic, ilovepiPull Request:#87573
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‎llvm/docs/CalleeTypeMetadata.rst

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====================
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Callee Type Metadata
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====================
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Introduction
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============
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This ``!callee_type`` metadata is introduced to support the generation of a call graph
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section in the object file. The ``!callee_type`` metadata is used
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to identify the types of the intended callees of indirect call instructions. The ``!callee_type`` metadata is a
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list of one or more generalized ``!type`` metadata objects (See:doc:`TypeMetadata`) with each ``!type``
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metadata pointing to a callee's:ref:`type identifier<calleetype-type-identifier>`.
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LLVM's `Control Flow Integrity (CFI)`_ also uses the ``!type`` metadata in its implementation.
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.. _Control Flow Integrity (CFI):https://clang.llvm.org/docs/ControlFlowIntegrity.html
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.. _calleetype-type-identifier:
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Type identifier
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================
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The type for an indirect call target is the callee's function signature.
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Mapping from a type to an identifier is an ABI detail.
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In the current implementation, an identifier of type T is
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computed as follows:
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- Obtain the generalized mangled name for “typeinfo name for T”.
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- Compute MD5 hash of the name as a string.
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- Reinterpret the first 8 bytes of the hash as a little-endian 64-bit integer.
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To avoid mismatched pointer types, generalizations are applied.
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Pointers in return and argument types are treated as equivalent as long as the qualifiers for the
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type they point to match. For example, ``char*``, ``char**``, and ``int*`` are considered equivalent
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types. However, ``char*`` and ``const char*`` are considered distinct types.

‎llvm/docs/LangRef.rst

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@@ -8171,6 +8171,11 @@ change in the future.
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See :doc:`TypeMetadata`.
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'``callee_type``' Metadata
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^^^^^^^^^^^^^^^^^^^^^^^^^^
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See :doc:`CalleeTypeMetadata`.
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'``associated``' Metadata
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^^^^^^^^^^^^^^^^^^^^^^^^^
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‎llvm/docs/Reference.rst

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@@ -14,6 +14,7 @@ LLVM and API reference documentation.
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BlockFrequencyTerminology
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BranchWeightMetadata
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Bugpoint
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CalleeTypeMetadata
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CIBestPractices
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CommandGuide/index
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ConvergenceAndUniformity

‎llvm/include/llvm/IR/FixedMetadataKinds.def

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@@ -53,3 +53,4 @@ LLVM_FIXED_MD_KIND(MD_DIAssignID, "DIAssignID", 38)
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LLVM_FIXED_MD_KIND(MD_coro_outside_frame,"coro.outside.frame",39)
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LLVM_FIXED_MD_KIND(MD_mmra,"mmra",40)
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LLVM_FIXED_MD_KIND(MD_noalias_addrspace,"noalias.addrspace",41)
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LLVM_FIXED_MD_KIND(MD_callee_type,"callee_type",42)

‎llvm/include/llvm/IR/Metadata.h

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@@ -1255,6 +1255,13 @@ class MDNode : public Metadata {
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boolisReplaceable()const {returnisTemporary() ||isAlwaysReplaceable(); }
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boolisAlwaysReplaceable()const {returngetMetadataID() == DIAssignIDKind; }
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/// Check if this is a valid generalized type metadata node.
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boolhasGeneralizedMDString() {
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if (getNumOperands() <2 || !isa<MDString>(getOperand(1)))
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returnfalse;
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return cast<MDString>(getOperand(1))->getString().ends_with(".generalized");
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}
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unsignedgetNumTemporaryUses()const {
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assert(isTemporary() &&"Only for temporaries");
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return Context.getReplaceableUses()->getNumUses();
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const Instruction *BInstr);
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LLVM_ABIstatic MDNode *getMergedMemProfMetadata(MDNode *A, MDNode *B);
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LLVM_ABIstatic MDNode *getMergedCallsiteMetadata(MDNode *A, MDNode *B);
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LLVM_ABIstatic MDNode *getMergedCalleeTypeMetadata(const MDNode *A,
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const MDNode *B);
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};
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/// Tuple of metadata.

‎llvm/lib/IR/Metadata.cpp

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@@ -1303,6 +1303,24 @@ static void addRange(SmallVectorImpl<ConstantInt *> &EndPoints,
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EndPoints.push_back(High);
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}
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MDNode *MDNode::getMergedCalleeTypeMetadata(const MDNode *A,const MDNode *B) {
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// Drop the callee_type metadata if either of the call instructions do not
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// have it.
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if (!A || !B)
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returnnullptr;
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SmallVector<Metadata *,8> AB;
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SmallPtrSet<Metadata *,8> MergedCallees;
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auto AddUniqueCallees = [&AB, &MergedCallees](const MDNode *N) {
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for (Metadata *MD : N->operands()) {
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if (MergedCallees.insert(MD).second)
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AB.push_back(MD);
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}
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};
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AddUniqueCallees(A);
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AddUniqueCallees(B);
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returnMDNode::get(A->getContext(), AB);
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}
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MDNode *MDNode::getMostGenericRange(MDNode *A, MDNode *B) {
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// Given two ranges, we want to compute the union of the ranges. This
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// is slightly complicated by having to combine the intervals and merge

‎llvm/lib/IR/Verifier.cpp

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@@ -531,6 +531,7 @@ class Verifier : public InstVisitor<Verifier>, VerifierSupport {
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voidvisitCallStackMetadata(MDNode *MD);
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voidvisitMemProfMetadata(Instruction &I, MDNode *MD);
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voidvisitCallsiteMetadata(Instruction &I, MDNode *MD);
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voidvisitCalleeTypeMetadata(Instruction &I, MDNode *MD);
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voidvisitDIAssignIDMetadata(Instruction &I, MDNode *MD);
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voidvisitMMRAMetadata(Instruction &I, MDNode *MD);
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voidvisitAnnotationMetadata(MDNode *Annotation);
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visitCallStackMetadata(MD);
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}
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staticinlineboolisConstantIntMetadataOperand(const Metadata *MD) {
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if (auto *VAL = dyn_cast<ValueAsMetadata>(MD))
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return isa<ConstantInt>(VAL->getValue());
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returnfalse;
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}
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voidVerifier::visitCalleeTypeMetadata(Instruction &I, MDNode *MD) {
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Check(isa<CallBase>(I),"!callee_type metadata should only exist on calls",
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&I);
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for (Metadata *Op : MD->operands()) {
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Check(isa<MDNode>(Op),
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"The callee_type metadata must be a list of type metadata nodes", Op);
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auto *TypeMD = cast<MDNode>(Op);
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Check(TypeMD->getNumOperands() ==2,
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"Well-formed generalized type metadata must contain exactly two"
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"operands",
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Op);
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Check(isConstantIntMetadataOperand(TypeMD->getOperand(0)) &&
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mdconst::extract<ConstantInt>(TypeMD->getOperand(0))->isZero(),
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"The first operand of type metadata for functions must be zero", Op);
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Check(TypeMD->hasGeneralizedMDString(),
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"Only generalized type metadata can be part of the callee_type"
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"metadata list",
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Op);
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}
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}
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voidVerifier::visitAnnotationMetadata(MDNode *Annotation) {
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Check(isa<MDTuple>(Annotation),"annotation must be a tuple");
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Check(Annotation->getNumOperands() >=1,
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if (MDNode *MD = I.getMetadata(LLVMContext::MD_callsite))
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visitCallsiteMetadata(I, MD);
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if (MDNode *MD = I.getMetadata(LLVMContext::MD_callee_type))
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visitCalleeTypeMetadata(I, MD);
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if (MDNode *MD = I.getMetadata(LLVMContext::MD_DIAssignID))
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visitDIAssignIDMetadata(I, MD);
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‎llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

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@@ -4352,6 +4352,13 @@ Instruction *InstCombinerImpl::visitCallBase(CallBase &Call) {
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Call, Builder.CreateBitOrPointerCast(ReturnedArg, CallTy));
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}
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// Drop unnecessary callee_type metadata from calls that were converted
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// into direct calls.
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if (Call.getMetadata(LLVMContext::MD_callee_type) && !Call.isIndirectCall()) {
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Call.setMetadata(LLVMContext::MD_callee_type,nullptr);
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Changed =true;
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}
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// Drop unnecessary kcfi operand bundles from calls that were converted
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// into direct calls.
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auto Bundle = Call.getOperandBundle(LLVMContext::OB_kcfi);

‎llvm/lib/Transforms/Utils/Local.cpp

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@@ -3005,6 +3005,12 @@ static void combineMetadata(Instruction *K, const Instruction *J,
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case LLVMContext::MD_memprof:
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case LLVMContext::MD_callsite:
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break;
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case LLVMContext::MD_callee_type:
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if (!AAOnly) {
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K->setMetadata(LLVMContext::MD_callee_type,
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MDNode::getMergedCalleeTypeMetadata(KMD, JMD));
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}
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break;
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case LLVMContext::MD_align:
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if (!AAOnly && (DoesKMove || !K->hasMetadata(LLVMContext::MD_noundef)))
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K->setMetadata(

‎llvm/lib/Transforms/Utils/ValueMapper.cpp

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@@ -987,6 +987,13 @@ void Mapper::remapInstruction(Instruction *I) {
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"Referenced value not in value map!");
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}
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// Drop callee_type metadata from calls that were remapped
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// into a direct call from an indirect one.
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if (auto *CB = dyn_cast<CallBase>(I)) {
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if (CB->getMetadata(LLVMContext::MD_callee_type) && !CB->isIndirectCall())
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CB->setMetadata(LLVMContext::MD_callee_type,nullptr);
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}
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// Remap phi nodes' incoming blocks.
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if (PHINode *PN = dyn_cast<PHINode>(I)) {
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for (unsigned i =0, e = PN->getNumIncomingValues(); i != e; ++i) {

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