[PATCH] D57267: [AST] Factor out the logic of the various Expr::Ignore*

[Bruno Ricci via Phabricator via cfe-commits]

riccibruno added inline comments.


================
Comment at: lib/AST/Expr.cpp:2562
+    return ICE->getSubExpr();
+
+  else if (auto *FE = dyn_cast_or_null<FullExpr>(E))
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It is something that is actually possible to audit. I did look at where each of the skipped node are created and it *seems* that a null child is not possible. However it is very easy to miss a case and adding the null check give the various `Expr::Ignore*` the following nice property:

Regardless of the state of the AST, for every expression `E` (null or not). `Ignore*(E)` produces the correct result (which may be null).

But perhaps the correct invariant to maintain is that these nodes have always a non-null child ?

I re-ran the benchmarks more carefully and here are the results I got (on my usual benchmark: `-fyntax-only` on all of Boost, 20 iterations with `perf stat`):

8.2117 +- 0.0131 seconds (with the null check)
8.2028 +- 0.0058 seconds (without the null check)


================
Comment at: lib/AST/Expr.cpp:2695
+/// Note that a null E is valid; in this case nothing is done.
+template <typename... FnTys> Expr *IgnoreExprNodes(Expr *E, FnTys &&... Fns) {
   Expr *LastE = nullptr;
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aaron.ballman wrote:
> Formatting looks off here, did clang-format produce this?
It did, though with the `static` specifier `clang-format` adds a new line.


Repository:
  rC Clang

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D57267/new/

https://reviews.llvm.org/D57267