[PATCH] D87822: [FPEnv] Evaluate constant expressions under non-default rounding modes

[John McCall via Phabricator via cfe-commits]

rjmccall added inline comments.


================
Comment at: clang/lib/AST/ExprConstant.cpp:2462
+  return true;
+}
+
----------------
Thanks, these look good.


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Comment at: clang/lib/AST/ExprConstant.cpp:2427
+    FPOptions FPFeatures = Cast->getFPFeaturesInEffect(Info.Ctx.getLangOpts());
+    RM = FPFeatures.getRoundingMode();
+  }
----------------
sepavloff wrote:
> rjmccall wrote:
> > I think the options really need to be passed in or else correctness is somewhat doomed here.
> > 
> > For example, the call to CompoundAssignSubobjectHandler needs to propagate this down from the operator expression.
> It is guaranteed by the way AST is built, no?
> 
> As FP options may be changed only by pragmas and the pragmas can be specified only at file or block level, all sub-expression are evaluated at the same options.
Yes, but you can't actually reliably recover those settings from E unless you're sure E is one of a few kinds of expression.  The concern is that E might end up being some closely-related expression that isn't actually the expression that carries the current settings, and then we'll fall back on using the global defaults.  It's much more correct-by-construction to pass the settings down from the caller based on the caller's static knowledge of which expression is under consideration, and I think you'll see that that's pretty straightforward in practice.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D87822/new/

https://reviews.llvm.org/D87822