[memprof] Use SmallVector for InlinedCallStack (NFC)

We can stay within 8 inlined elements more than 99% of the time while
building a large application.

Author: kazutakahirata

llvm/lib/Analysis/MemoryProfileInfo.cpp

@@ -69,7 +69,8 @@ AllocationType llvm::memprof::getAllocType(uint64_t TotalLifetimeAccessDensity,
 
 MDNode *llvm::memprof::buildCallstackMetadata(ArrayRef<uint64_t> CallStack,
                                               LLVMContext &Ctx) {
-  std::vector<Metadata *> StackVals;
+  SmallVector<Metadata *, 8> StackVals;
+  StackVals.reserve(CallStack.size());
   for (auto Id : CallStack) {
     auto *StackValMD =
         ValueAsMetadata::get(ConstantInt::get(Type::getInt64Ty(Ctx), Id));

llvm/lib/Transforms/Instrumentation/MemProfiler.cpp

@@ -680,7 +680,7 @@ bool MemProfiler::instrumentFunction(Function &F) {
 }
 
 static void addCallsiteMetadata(Instruction &I,
-                                std::vector<uint64_t> &InlinedCallStack,
+                                ArrayRef<uint64_t> InlinedCallStack,
                                 LLVMContext &Ctx) {
   I.setMetadata(LLVMContext::MD_callsite,
                 buildCallstackMetadata(InlinedCallStack, Ctx));
@@ -905,7 +905,7 @@ readMemprof(Module &M, Function &F, IndexedInstrProfReader *MemProfReader,
         continue;
       // List of call stack ids computed from the location hashes on debug
       // locations (leaf to inlined at root).
-      std::vector<uint64_t> InlinedCallStack;
+      SmallVector<uint64_t, 8> InlinedCallStack;
       // Was the leaf location found in one of the profile maps?
       bool LeafFound = false;
       // If leaf was found in a map, iterators pointing to its location in both