1 files changed, 102 insertions, 36 deletions

diff --git a/contrib/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp b/contrib/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
index 49ef1e7..911c14e 100644
--- a/contrib/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
+++ b/contrib/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
@@ -211,7 +211,9 @@ void DAE::CollectFunctionDIs(Module &M) {
       for (unsigned SPIndex = 0, SPNum = SPs.getNumElements();
            SPIndex < SPNum; ++SPIndex) {
         DISubprogram SP(SPs.getElement(SPIndex));
-        if (!SP.Verify())
+        assert((!SP || SP.isSubprogram()) &&
+          "A MDNode in subprograms of a CU should be null or a DISubprogram.");
+        if (!SP)
           continue;
         if (Function *F = SP.getFunction())
           FunctionDIs[F] = SP;
@@ -263,8 +265,10 @@ bool DAE::DeleteDeadVarargs(Function &Fn) {
   // to pass in a smaller number of arguments into the new function.
   //
   std::vector<Value*> Args;
-  while (!Fn.use_empty()) {
-    CallSite CS(Fn.use_back());
+  for (Value::use_iterator I = Fn.use_begin(), E = Fn.use_end(); I != E; ) {
+    CallSite CS(*I++);
+    if (!CS)
+      continue;
     Instruction *Call = CS.getInstruction();
 
     // Pass all the same arguments.
@@ -330,6 +334,11 @@ bool DAE::DeleteDeadVarargs(Function &Fn) {
   if (DI != FunctionDIs.end())
     DI->second.replaceFunction(NF);
 
+  // Fix up any BlockAddresses that refer to the function.
+  Fn.replaceAllUsesWith(ConstantExpr::getBitCast(NF, Fn.getType()));
+  // Delete the bitcast that we just created, so that NF does not
+  // appear to be address-taken.
+  NF->removeDeadConstantUsers();
   // Finally, nuke the old function.
   Fn.eraseFromParent();
   return true;
@@ -343,8 +352,22 @@ bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
   if (Fn.isDeclaration() || Fn.mayBeOverridden())
     return false;
 
-  // Functions with local linkage should already have been handled.
-  if (Fn.hasLocalLinkage())
+  // Functions with local linkage should already have been handled, except the
+  // fragile (variadic) ones which we can improve here.
+  if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg())
+    return false;
+
+  // If a function seen at compile time is not necessarily the one linked to
+  // the binary being built, it is illegal to change the actual arguments
+  // passed to it. These functions can be captured by isWeakForLinker().
+  // *NOTE* that mayBeOverridden() is insufficient for this purpose as it
+  // doesn't include linkage types like AvailableExternallyLinkage and
+  // LinkOnceODRLinkage. Take link_odr* as an example, it indicates a set of
+  // *EQUIVALENT* globals that can be merged at link-time. However, the
+  // semantic of *EQUIVALENT*-functions includes parameters. Changing
+  // parameters breaks this assumption.
+  //
+  if (Fn.isWeakForLinker())
     return false;
 
   if (Fn.use_empty())
@@ -604,9 +627,20 @@ void DAE::SurveyFunction(const Function &F) {
   UseVector MaybeLiveArgUses;
   for (Function::const_arg_iterator AI = F.arg_begin(),
        E = F.arg_end(); AI != E; ++AI, ++i) {
-    // See what the effect of this use is (recording any uses that cause
-    // MaybeLive in MaybeLiveArgUses).
-    Liveness Result = SurveyUses(AI, MaybeLiveArgUses);
+    Liveness Result;
+    if (F.getFunctionType()->isVarArg()) {
+      // Variadic functions will already have a va_arg function expanded inside
+      // them, making them potentially very sensitive to ABI changes resulting
+      // from removing arguments entirely, so don't. For example AArch64 handles
+      // register and stack HFAs very differently, and this is reflected in the
+      // IR which has already been generated.
+      Result = Live;
+    } else {
+      // See what the effect of this use is (recording any uses that cause
+      // MaybeLive in MaybeLiveArgUses). 
+      Result = SurveyUses(AI, MaybeLiveArgUses);
+    }
+
     // Mark the result.
     MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
     // Clear the vector again for the next iteration.
@@ -695,10 +729,42 @@ bool DAE::RemoveDeadStuffFromFunction(Function *F) {
   FunctionType *FTy = F->getFunctionType();
   std::vector<Type*> Params;
 
+  // Keep track of if we have a live 'returned' argument
+  bool HasLiveReturnedArg = false;
+
   // Set up to build a new list of parameter attributes.
   SmallVector<AttributeSet, 8> AttributesVec;
   const AttributeSet &PAL = F->getAttributes();
 
+  // Remember which arguments are still alive.
+  SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
+  // Construct the new parameter list from non-dead arguments. Also construct
+  // a new set of parameter attributes to correspond. Skip the first parameter
+  // attribute, since that belongs to the return value.
+  unsigned i = 0;
+  for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
+       I != E; ++I, ++i) {
+    RetOrArg Arg = CreateArg(F, i);
+    if (LiveValues.erase(Arg)) {
+      Params.push_back(I->getType());
+      ArgAlive[i] = true;
+
+      // Get the original parameter attributes (skipping the first one, that is
+      // for the return value.
+      if (PAL.hasAttributes(i + 1)) {
+        AttrBuilder B(PAL, i + 1);
+        if (B.contains(Attribute::Returned))
+          HasLiveReturnedArg = true;
+        AttributesVec.
+          push_back(AttributeSet::get(F->getContext(), Params.size(), B));
+      }
+    } else {
+      ++NumArgumentsEliminated;
+      DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName()
+            << ") from " << F->getName() << "\n");
+    }
+  }
+
   // Find out the new return value.
   Type *RetTy = FTy->getReturnType();
   Type *NRetTy = NULL;
@@ -707,7 +773,27 @@ bool DAE::RemoveDeadStuffFromFunction(Function *F) {
   // -1 means unused, other numbers are the new index
   SmallVector<int, 5> NewRetIdxs(RetCount, -1);
   std::vector<Type*> RetTypes;
-  if (RetTy->isVoidTy()) {
+
+  // If there is a function with a live 'returned' argument but a dead return
+  // value, then there are two possible actions:
+  // 1) Eliminate the return value and take off the 'returned' attribute on the
+  //    argument.
+  // 2) Retain the 'returned' attribute and treat the return value (but not the
+  //    entire function) as live so that it is not eliminated.
+  // 
+  // It's not clear in the general case which option is more profitable because,
+  // even in the absence of explicit uses of the return value, code generation
+  // is free to use the 'returned' attribute to do things like eliding
+  // save/restores of registers across calls. Whether or not this happens is
+  // target and ABI-specific as well as depending on the amount of register
+  // pressure, so there's no good way for an IR-level pass to figure this out.
+  //
+  // Fortunately, the only places where 'returned' is currently generated by
+  // the FE are places where 'returned' is basically free and almost always a
+  // performance win, so the second option can just be used always for now.
+  //
+  // This should be revisited if 'returned' is ever applied more liberally.
+  if (RetTy->isVoidTy() || HasLiveReturnedArg) {
     NRetTy = RetTy;
   } else {
     StructType *STy = dyn_cast<StructType>(RetTy);
@@ -777,33 +863,6 @@ bool DAE::RemoveDeadStuffFromFunction(Function *F) {
   if (RAttrs.hasAttributes(AttributeSet::ReturnIndex))
     AttributesVec.push_back(AttributeSet::get(NRetTy->getContext(), RAttrs));
 
-  // Remember which arguments are still alive.
-  SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
-  // Construct the new parameter list from non-dead arguments. Also construct
-  // a new set of parameter attributes to correspond. Skip the first parameter
-  // attribute, since that belongs to the return value.
-  unsigned i = 0;
-  for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
-       I != E; ++I, ++i) {
-    RetOrArg Arg = CreateArg(F, i);
-    if (LiveValues.erase(Arg)) {
-      Params.push_back(I->getType());
-      ArgAlive[i] = true;
-
-      // Get the original parameter attributes (skipping the first one, that is
-      // for the return value.
-      if (PAL.hasAttributes(i + 1)) {
-        AttrBuilder B(PAL, i + 1);
-        AttributesVec.
-          push_back(AttributeSet::get(F->getContext(), Params.size(), B));
-      }
-    } else {
-      ++NumArgumentsEliminated;
-      DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName()
-            << ") from " << F->getName() << "\n");
-    }
-  }
-
   if (PAL.hasAttributes(AttributeSet::FunctionIndex))
     AttributesVec.push_back(AttributeSet::get(F->getContext(),
                                               PAL.getFnAttributes()));
@@ -864,6 +923,13 @@ bool DAE::RemoveDeadStuffFromFunction(Function *F) {
         // Get original parameter attributes, but skip return attributes.
         if (CallPAL.hasAttributes(i + 1)) {
           AttrBuilder B(CallPAL, i + 1);
+          // If the return type has changed, then get rid of 'returned' on the
+          // call site. The alternative is to make all 'returned' attributes on
+          // call sites keep the return value alive just like 'returned'
+          // attributes on function declaration but it's less clearly a win
+          // and this is not an expected case anyway
+          if (NRetTy != RetTy && B.contains(Attribute::Returned))
+            B.removeAttribute(Attribute::Returned);
           AttributesVec.
             push_back(AttributeSet::get(F->getContext(), Args.size(), B));
         }