[PATCH] D130600: [clang][dataflow] Handle return statements

Stanislav Gatev via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Thu Aug 4 05:26:19 PDT 2022

sgatev added inline comments.

Comment at: clang/lib/Analysis/FlowSensitive/Transfer.cpp:348
+    auto *Loc = Env.getReturnStorageLocation();
+    assert(Loc != nullptr);
+    // FIXME: Model NRVO.
samestep wrote:
> sgatev wrote:
> > Let's do `if (Loc == nullptr) return;`
> I don't think we want to do that, right? Shouldn't the `return` storage location always be set? Or is this about the "analyzing fragments rather than full functions" thing we discussed yesterday?
I think it's related. If we are going with always initializing the `return` storage location then I guess at some point we should be able to make `Environment::getReturnStorageLocation` return a reference? In that case I'm fine with keeping the assert around in the meantime.

Comment at: clang/lib/Analysis/FlowSensitive/Transfer.cpp:564
+      assert(ReturnLoc != nullptr);
+      Env.setStorageLocation(*S, *ReturnLoc);
+      Env.popCall(ExitEnv);
samestep wrote:
> sgatev wrote:
> > We use stable storage locations to ensure convergence. In that spirit, shouldn't we assign `ReturnLoc`'s value to `S`'s storage location instead of changing the storage location? Alternatively, we can pass `S`'s storage location to `pushCall` so that it can store it as `ReturnLoc`.
> Could you clarify how this hurts convergence? My understanding is that `ReturnLoc` here is already stable, so this would make `S`'s storage location stable too.
If I follow correctly, `ReturnLoc` here is the result of `Env.createStorageLocation(ReturnType)` which isn't stable. Each call to `createStorageLocation` returns a fresh storage location.

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