Do not specialize IRBuilder to strip names in SROA

[mehdi_amini]

Summary

Following r263086, we are replacing this by a runtime check.
More cleanup will follow on the IRBuilder itself, but I submitted
this patch separately as SROA has a fancy "prefixInserter" class
that needs extra-love.

[chandlerc]

FYI i've been reviewing these and I'll LGTM them as soon as we're clearly on the same page with Philip in D17946's thread.

[chandlerc]

LGTM patch is fine, but also see comment below.

lib/Transforms/Scalar/SROA.cpp

93–104

When you measured, did you measure getting rid of this complexity too?

If it doesn't slow SROA down when the context has the flag set, I would be all in favor of just completely removing the NDEBUG hacking here. My expectation is that the overhead of this while not zero (it uses an actual std::string) is *very* close to zero.

That said, if you'd rather submit as-is, I can take care of cleaning this up.

[mehdi_amini]

Remove NDEBUG ifdef in IRBuilderPrefixedInserter

[mehdi_amini]

r263256

lib/Transforms/Scalar/SROA.cpp

static cl::opt<bool> SROARandomShuffleSlices("sroa-random-shuffle-slices",
                                              cl::init(false), cl::Hidden);
 
 /// Hidden option to experiment with completely strict handling of inbounds
 /// GEPs.
 static cl::opt<bool> SROAStrictInbounds("sroa-strict-inbounds", cl::init(false),
                                         cl::Hidden);
 
 namespace {
-/// \brief A custom IRBuilder inserter which prefixes all names if they are
-/// preserved.
-template <bool preserveNames = true>
-class IRBuilderPrefixedInserter
-    : public IRBuilderDefaultInserter<preserveNames> {
+/// \brief A custom IRBuilder inserter which prefixes all names, but only in
+/// Assert builds.
+class IRBuilderPrefixedInserter : public IRBuilderDefaultInserter<true> {
   std::string Prefix;
+  const Twine getNameWithPrefix(const Twine &Name) const {
+    return Name.isTriviallyEmpty() ? Name : Prefix + Name;
+  }
 
 public:
   void SetNamePrefix(const Twine &P) { Prefix = P.str(); }
 
 protected:
   void InsertHelper(Instruction *I, const Twine &Name, BasicBlock *BB,
                     BasicBlock::iterator InsertPt) const {
-    IRBuilderDefaultInserter<preserveNames>::InsertHelper(
-        I, Name.isTriviallyEmpty() ? Name : Prefix + Name, BB, InsertPt);
+    IRBuilderDefaultInserter<true>::InsertHelper(I, getNameWithPrefix(Name), BB,
+                                                 InsertPt);
   }
 };
 
-// Specialization for not preserving the name is trivial.
-template <>
-class IRBuilderPrefixedInserter<false>
-    : public IRBuilderDefaultInserter<false> {
-public:
-  void SetNamePrefix(const Twine &P) {}
-};
-
 /// \brief Provide a typedef for IRBuilder that drops names in release builds.
-#ifndef NDEBUG
-typedef llvm::IRBuilder<true, ConstantFolder, IRBuilderPrefixedInserter<true>>
-    IRBuilderTy;
-#else
-typedef llvm::IRBuilder<false, ConstantFolder, IRBuilderPrefixedInserter<false>>
-    IRBuilderTy;
-#endif
+using IRBuilderTy =
+    llvm::IRBuilder<true, ConstantFolder, IRBuilderPrefixedInserter>;
 }
 
 namespace {
 /// \brief A used slice of an alloca.
 ///
 /// This structure represents a slice of an alloca used by some instruction. It
 /// stores both the begin and end offsets of this use, a pointer to the use
 /// itself, and a flag indicating whether we can classify the use as splittable