[SimplifyLibcalls] Remove the hasOneUse() limitation on the malloc

[xbolva00]

Summary

Discussion and part of https://reviews.llvm.org/D45344

The reason that's there is discussed in D16337 - the transform must be made safe from intermediate stores.

lib/Transforms/Utils/SimplifyLibCalls.cpp

 /// Fold memset[_chk](malloc(n), 0, n) --> calloc(1, n).
 static Value *foldMallocMemset(CallInst *Memset, IRBuilder<> &B,
                                const TargetLibraryInfo &TLI) {
   // This has to be a memset of zeros (bzero).
   auto *FillValue = dyn_cast<ConstantInt>(Memset->getArgOperand(1));
   if (!FillValue || FillValue->getZExtValue() != 0)
     return nullptr;
 
-  // TODO: We should handle the case where the malloc has more than one use.
-  // This is necessary to optimize common patterns such as when the result of
-  // the malloc is checked against null or when a memset intrinsic is used in
-  // place of a memset library call.
   auto *Malloc = dyn_cast<CallInst>(Memset->getArgOperand(0));
-  if (!Malloc || !Malloc->hasOneUse())
+  if (!Malloc)
     return nullptr;
 
   // Is the inner call really malloc()?
   Function *InnerCallee = Malloc->getCalledFunction();
   if (!InnerCallee)
     return nullptr;
 
   LibFunc Func;