Fix memory issue in AttrBuilder::removeAttribute uses

[dstenb]

Summary

Found when running Valgrind.

This removes two unnecessary assignments when using AttrBuilder::removeAttribute.

AttrBuilder::removeAttribute returns a reference to the object. As the LHSes were the same as the callees, the assignments resulted in memcpy calls where dst = src.

[rnk]

lgtm

llvm/trunk/lib/CodeGen/Analysis.cpp

bool llvm::attributesPermitTailCall(const Function *F, const Instruction *I,
 
   AttrBuilder CallerAttrs(F->getAttributes(),
                           AttributeSet::ReturnIndex);
   AttrBuilder CalleeAttrs(cast<CallInst>(I)->getAttributes(),
                           AttributeSet::ReturnIndex);
 
   // Noalias is completely benign as far as calling convention goes, it
   // shouldn't affect whether the call is a tail call.
-  CallerAttrs = CallerAttrs.removeAttribute(Attribute::NoAlias);
-  CalleeAttrs = CalleeAttrs.removeAttribute(Attribute::NoAlias);
+  CallerAttrs.removeAttribute(Attribute::NoAlias);
+  CalleeAttrs.removeAttribute(Attribute::NoAlias);
 
   if (CallerAttrs.contains(Attribute::ZExt)) {
     if (!CalleeAttrs.contains(Attribute::ZExt))
       return false;
 
     ADS = false;
     CallerAttrs.removeAttribute(Attribute::ZExt);
     CalleeAttrs.removeAttribute(Attribute::ZExt);