Don't replace an alias in llvm.used with its target.

When we replace an internal alias with its target, be careful not to
replace the entry in llvm.used (and llvm.compiler_used).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181524 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/IPO/GlobalOpt.cpp

@@ -3041,6 +3041,105 @@ bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) {
   return true;
 }
 
+static Value::use_iterator getFirst(Value *V, SmallPtrSet<Use*, 8> &Tried) {
+  for (Value::use_iterator I = V->use_begin(), E = V->use_end(); I != E; ++I) {
+    Use *U = &I.getUse();
+    if (Tried.count(U))
+      continue;
+
+    User *Usr = *I;
+    GlobalVariable *GV = dyn_cast<GlobalVariable>(Usr);
+    if (!GV || !GV->hasName()) {
+      Tried.insert(U);
+      return I;
+    }
+
+    StringRef Name = GV->getName();
+    if (Name != "llvm.used" && Name != "llvm.compiler_used") {
+      Tried.insert(U);
+      return I;
+    }
+  }
+  return V->use_end();
+}
+
+static bool replaceAllNonLLVMUsedUsesWith(Constant *Old, Constant *New);
+
+static bool replaceUsesOfWithOnConstant(ConstantArray *CA, Value *From,
+                                        Value *ToV, Use *U) {
+  Constant *To = cast<Constant>(ToV);
+
+  SmallVector<Constant*, 8> NewOps;
+  for (unsigned i = 0, e = CA->getNumOperands(); i != e; ++i) {
+    Constant *Op = CA->getOperand(i);
+    NewOps.push_back(Op == From ? To : Op);
+  }
+
+  Constant *Replacement = ConstantArray::get(CA->getType(), NewOps);
+  assert(Replacement != CA && "CA didn't contain From!");
+
+  bool Ret = replaceAllNonLLVMUsedUsesWith(CA, Replacement);
+  if (Replacement->use_empty())
+    Replacement->destroyConstant();
+  if (CA->use_empty())
+    CA->destroyConstant();
+  return Ret;
+}
+
+static bool replaceUsesOfWithOnConstant(ConstantExpr *CE, Value *From,
+                                        Value *ToV, Use *U) {
+  Constant *To = cast<Constant>(ToV);
+  SmallVector<Constant*, 8> NewOps;
+  for (unsigned i = 0, e = CE->getNumOperands(); i != e; ++i) {
+    Constant *Op = CE->getOperand(i);
+    NewOps.push_back(Op == From ? To : Op);
+  }
+
+  Constant *Replacement = CE->getWithOperands(NewOps);
+  assert(Replacement != CE && "CE didn't contain From!");
+
+  bool Ret = replaceAllNonLLVMUsedUsesWith(CE, Replacement);
+  if (Replacement->use_empty())
+    Replacement->destroyConstant();
+  if (CE->use_empty())
+    CE->destroyConstant();
+  return Ret;
+}
+
+static bool replaceUsesOfWithOnConstant(Constant *C, Value *From, Value *To,
+                                        Use *U) {
+  if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
+    return replaceUsesOfWithOnConstant(CA, From, To, U);
+  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
+    return replaceUsesOfWithOnConstant(CE, From, To, U);
+  C->replaceUsesOfWithOnConstant(From, To, U);
+  return true;
+}
+
+static bool replaceAllNonLLVMUsedUsesWith(Constant *Old, Constant *New) {
+  SmallPtrSet<Use*, 8> Tried;
+  bool Ret = false;
+  for (;;) {
+    Value::use_iterator I = getFirst(Old, Tried);
+    if (I == Old->use_end())
+      break;
+    Use &U = I.getUse();
+
+    // Must handle Constants specially, we cannot call replaceUsesOfWith on a
+    // constant because they are uniqued.
+    if (Constant *C = dyn_cast<Constant>(U.getUser())) {
+      if (!isa<GlobalValue>(C)) {
+        Ret |= replaceUsesOfWithOnConstant(C, Old, New, &U);
+        continue;
+      }
+    }
+
+    U.set(New);
+    Ret = true;
+  }
+  return Ret;
+}
+
 bool GlobalOpt::OptimizeGlobalAliases(Module &M) {
   bool Changed = false;
 
@@ -3060,11 +3159,12 @@ bool GlobalOpt::OptimizeGlobalAliases(Module &M) {
     bool hasOneUse = Target->hasOneUse() && Aliasee->hasOneUse();
 
     // Make all users of the alias use the aliasee instead.
-    if (!J->use_empty()) {
+    if (replaceAllNonLLVMUsedUsesWith(J, Aliasee)) {
-      J->replaceAllUsesWith(Aliasee);
       ++NumAliasesResolved;
       Changed = true;
     }
+    if (!J->use_empty())
+      continue;
 
     // If the alias is externally visible, we may still be able to simplify it.
     if (!J->hasLocalLinkage()) {

test/Transforms/GlobalOpt/alias-used.ll

@@ -0,0 +1,42 @@
+; RUN: opt < %s -globalopt -S | FileCheck %s
+
+@c = global i8 42
+
+@llvm.used = appending global [3 x i8*] [i8* bitcast (void ()* @fa to i8*), i8* bitcast (void ()* @f to i8*), i8* @ca], section "llvm.metadata"
+; CHECK: @llvm.used = appending global [3 x i8*] [i8* bitcast (void ()* @fa to i8*), i8* bitcast (void ()* @f to i8*), i8* @ca], section "llvm.metadata"
+
+@llvm.compiler_used = appending global [2 x i8*] [i8* bitcast (void ()* @fa to i8*), i8* bitcast (void ()* @fa3 to i8*)], section "llvm.metadata"
+
+@sameAsUsed = global [3 x i8*] [i8* bitcast (void ()* @fa to i8*), i8* bitcast (void ()* @f to i8*), i8* @ca]
+; CHECK: @sameAsUsed = global [3 x i8*] [i8* bitcast (void ()* @f to i8*), i8* bitcast (void ()* @f to i8*), i8* @c]
+
+@other = global i32* bitcast (void ()* @fa to i32*)
+; CHECK: @other = global i32* bitcast (void ()* @f to i32*)
+
+@fa = alias internal void ()* @f
+; CHECK: @fa = alias internal void ()* @f
+
+@fa2 = alias internal void ()* @f
+; CHECK-NOT: @fa2
+
+@fa3 = alias internal void ()* @f
+; CHECK: @fa3
+
+@ca = alias internal i8* @c
+; CHECK: @ca = alias internal i8* @c
+
+define void @f() {
+  ret void
+}
+
+define i8* @g() {
+  ret i8* bitcast (void ()* @fa to i8*);
+}
+
+define i8* @g2() {
+  ret i8* bitcast (void ()* @fa2 to i8*);
+}
+
+define i8* @h() {
+  ret i8* @ca
+}