Linker: Don't use MDNode::replaceOperandWith()

`MDNode::replaceOperandWith()` changes all instances of metadata.  Stop
using it when linking module flags, since (due to uniquing) the flag
values could be used by other metadata.

Instead, use new API `NamedMDNode::setOperand()` to update the reference
directly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225397 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/Metadata.h

@@ -847,6 +847,7 @@ public:
   MDNode *getOperand(unsigned i) const;
   unsigned getNumOperands() const;
   void addOperand(MDNode *M);
+  void setOperand(unsigned I, MDNode *New);
   StringRef getName() const;
   void print(raw_ostream &ROS) const;
   void dump() const;

lib/IR/Metadata.cpp

@@ -836,6 +836,11 @@ MDNode *NamedMDNode::getOperand(unsigned i) const {
 
 void NamedMDNode::addOperand(MDNode *M) { getNMDOps(Operands).emplace_back(M); }
 
+void NamedMDNode::setOperand(unsigned I, MDNode *New) {
+  assert(I < getNumOperands() && "Invalid operand number");
+  getNMDOps(Operands)[I].reset(New);
+}
+
 void NamedMDNode::eraseFromParent() {
   getParent()->eraseNamedMetadata(this);
 }

lib/Linker/LinkModules.cpp

@@ -1312,7 +1312,7 @@ bool ModuleLinker::linkModuleFlagsMetadata() {
   }
 
   // First build a map of the existing module flags and requirements.
-  DenseMap<MDString*, MDNode*> Flags;
+  DenseMap<MDString *, std::pair<MDNode *, unsigned>> Flags;
   SmallSetVector<MDNode*, 16> Requirements;
   for (unsigned I = 0, E = DstModFlags->getNumOperands(); I != E; ++I) {
     MDNode *Op = DstModFlags->getOperand(I);
@@ -1322,7 +1322,7 @@ bool ModuleLinker::linkModuleFlagsMetadata() {
     if (Behavior->getZExtValue() == Module::Require) {
       Requirements.insert(cast<MDNode>(Op->getOperand(2)));
     } else {
-      Flags[ID] = Op;
+      Flags[ID] = std::make_pair(Op, I);
     }
   }
 
@@ -1334,7 +1334,9 @@ bool ModuleLinker::linkModuleFlagsMetadata() {
     ConstantInt *SrcBehavior =
         mdconst::extract<ConstantInt>(SrcOp->getOperand(0));
     MDString *ID = cast<MDString>(SrcOp->getOperand(1));
-    MDNode *DstOp = Flags.lookup(ID);
+    MDNode *DstOp;
+    unsigned DstIndex;
+    std::tie(DstOp, DstIndex) = Flags.lookup(ID);
     unsigned SrcBehaviorValue = SrcBehavior->getZExtValue();
 
     // If this is a requirement, add it and continue.
@@ -1349,7 +1351,7 @@ bool ModuleLinker::linkModuleFlagsMetadata() {
 
     // If there is no existing flag with this ID, just add it.
     if (!DstOp) {
-      Flags[ID] = SrcOp;
+      Flags[ID] = std::make_pair(SrcOp, DstModFlags->getNumOperands());
       DstModFlags->addOperand(SrcOp);
       continue;
     }
@@ -1370,8 +1372,8 @@ bool ModuleLinker::linkModuleFlagsMetadata() {
       continue;
     } else if (SrcBehaviorValue == Module::Override) {
       // Update the destination flag to that of the source.
-      DstOp->replaceOperandWith(0, ConstantAsMetadata::get(SrcBehavior));
-      DstOp->replaceOperandWith(2, SrcOp->getOperand(2));
+      DstModFlags->setOperand(DstIndex, SrcOp);
+      Flags[ID].first = SrcOp;
       continue;
     }
 
@@ -1382,6 +1384,13 @@ bool ModuleLinker::linkModuleFlagsMetadata() {
       continue;
     }
 
+    auto replaceDstValue = [&](MDNode *New) {
+      Metadata *FlagOps[] = {DstOp->getOperand(0), ID, New};
+      MDNode *Flag = MDNode::get(DstM->getContext(), FlagOps);
+      DstModFlags->setOperand(DstIndex, Flag);
+      Flags[ID].first = Flag;
+    };
+
     // Perform the merge for standard behavior types.
     switch (SrcBehaviorValue) {
     case Module::Require:
@@ -1411,7 +1420,8 @@ bool ModuleLinker::linkModuleFlagsMetadata() {
         MDs.push_back(DstValue->getOperand(i));
       for (unsigned i = 0, e = SrcValue->getNumOperands(); i != e; ++i)
         MDs.push_back(SrcValue->getOperand(i));
-      DstOp->replaceOperandWith(2, MDNode::get(DstM->getContext(), MDs));
+
+      replaceDstValue(MDNode::get(DstM->getContext(), MDs));
       break;
     }
     case Module::AppendUnique: {
@@ -1422,8 +1432,8 @@ bool ModuleLinker::linkModuleFlagsMetadata() {
         Elts.insert(DstValue->getOperand(i));
       for (unsigned i = 0, e = SrcValue->getNumOperands(); i != e; ++i)
         Elts.insert(SrcValue->getOperand(i));
-      DstOp->replaceOperandWith(
-          2, MDNode::get(DstM->getContext(),
+
+      replaceDstValue(MDNode::get(DstM->getContext(),
                                   makeArrayRef(Elts.begin(), Elts.end())));
       break;
     }
@@ -1436,7 +1446,7 @@ bool ModuleLinker::linkModuleFlagsMetadata() {
     MDString *Flag = cast<MDString>(Requirement->getOperand(0));
     Metadata *ReqValue = Requirement->getOperand(1);
 
-    MDNode *Op = Flags[Flag];
+    MDNode *Op = Flags[Flag].first;
     if (!Op || Op->getOperand(2) != ReqValue) {
       HasErr |= emitError("linking module flags '" + Flag->getString() +
                           "': does not have the required value");

test/Linker/Inputs/module-flags-dont-change-others.ll

@@ -0,0 +1,8 @@
+!llvm.module.flags = !{!3, !4, !5}
+
+!0 = !{}
+!1 = !{!0}
+!2 = !{!0, !1}
+!3 = !{i32 4, !"foo", i32 37} ; Override the "foo" value.
+!4 = !{i32 5, !"bar", !1}
+!5 = !{i32 6, !"baz", !2}

test/Linker/module-flags-dont-change-others.ll

@@ -0,0 +1,26 @@
+; RUN: llvm-link %s %S/Inputs/module-flags-dont-change-others.ll -S -o - | FileCheck %s
+
+; Test that module-flag linking doesn't change other metadata.  In particular,
+; !named should still point at the unmodified tuples (!3, !4, and !5) that
+; happen to also serve as module flags.
+
+; CHECK: !named = !{!0, !1, !2, !3, !4, !5}
+; CHECK: !llvm.module.flags = !{!6, !7, !8}
+!named = !{!0, !1, !2, !3, !4, !5}
+!llvm.module.flags = !{!3, !4, !5}
+
+; CHECK: !0 = !{}
+; CHECK: !1 = !{!0}
+; CHECK: !2 = !{!0, !1}
+; CHECK: !3 = !{i32 1, !"foo", i32 927}
+; CHECK: !4 = !{i32 5, !"bar", !0}
+; CHECK: !5 = !{i32 6, !"baz", !1}
+; CHECK: !6 = !{i32 4, !"foo", i32 37}
+; CHECK: !7 = !{i32 5, !"bar", !1}
+; CHECK: !8 = !{i32 6, !"baz", !2}
+!0 = !{}
+!1 = !{!0}
+!2 = !{!0, !1}
+!3 = !{i32 1, !"foo", i32 927}
+!4 = !{i32 5, !"bar", !0}
+!5 = !{i32 6, !"baz", !1}