[Openmp-commits] [PATCH] D141968: [NFC] Consolidate llvm::CodeGenOpt::Level handling

Scott Linder via Phabricator via Openmp-commits openmp-commits at lists.llvm.org
Wed Jan 18 16:00:05 PST 2023

scott.linder added inline comments.

Comment at: llvm/include/llvm/Support/CodeGen.h:57
+  /// Code generation optimization level.
+  enum Level : IDType {
+    None = 0,      ///< -O0
barannikov88 wrote:
> arsenm wrote:
> > scott.linder wrote:
> > > This is ABI breaking, so maybe we don't want/need to define the underlying type?
> > This isn't in the C API, and this isn't for a release branch so I don't think it matters
> Why did you need to restrict the underlying type?
There is no strict need, it just:

* Avoids potential UB (casting an out-of-range value to an enumeration type //without a fixed underlying type// is undefined); in practice there is plenty of UB in LLVM, and a bug here wouldn't be a particularly pernicious kind of UB anyway.
* Means users of the type might pack better (and we won't run out of 255 opt levels anytime soon).

I originally intended to change this to an `enum class` rather than a `class` in a `namespace`, but that is slightly more disruptive and should probably be done for every other enumeration defined here at the same time.

Comment at: llvm/include/llvm/Support/CodeGen.h:67
+  inline std::optional<Level> getLevel(IDType ID) {
+    if (ID < 0 || ID > 3)
+      return std::nullopt;
barannikov88 wrote:
> As I can see, clients do not check for nullopt. Either add checks or replace this check with an assertion and drop std::optional (in this case `parseLevel` should be updated accordingly).
Good catch! I was working off of the old behavior of `llvm::Optional` and assuming the new `std::optional` was guaranteed to `assert` on dereference as well. I think the right interface is to expose the `optional`, so for the callsites which currently do the equivalent of asserting I will just carry over an explicit assert to the new version.

I posted to https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716/26 to discuss the issue more generally, as at least some of the patches which moved code from `llvm::Optional` to `std::optional` accidentally dropped assertions.

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