rsmith added inline comments.
================
Comment at: lib/CodeGen/CGExprConstant.cpp:1414-1415
+ Expr::EvalResult Result;
+ if (Init->EvaluateAsRValue(Result, CE.CGM.getContext()) &&
+ !Result.hasUnacceptableSideEffect(Expr::SE_NoSideEffects))
+ return (Result.Val.isInt() && Result.Val.getInt().isNullValue()) ||
----------------
sepavloff wrote:
> rsmith wrote:
> > Please call `D.evaluateValue()` here rather than inventing your own
> > evaluation scheme. That way, we'll cache the evaluated initializer on the
> > variable for other uses or reuse the value if we've already evaluated it,
> > and you don't need to worry about the corner cases involved in getting the
> > evaluation right. (As it happens, you're getting some minor details wrong
> > because evaluating an initializer is not quite the same as evaluating an
> > rvalue, but in practice it's not a big deal here.)
>
> Call of `D.evaluateValue()` may result in substantial memory and time
> consumption if the variable value is huge, like in:
> ```
> int char data_1[2147483648u] = { 0 };
> ```
> The idea of this patch is to recognize some cases of zero initialization
> prior to the evaluation of variable initializer. In the example above, value
> would be evaluated only for part of the initializer, namely `0`, which does
> not have an associated variable, so call of `D.evaluateValue()` is not
> possible.
>
As noted, `EvaluateAsRValue` gets some of the details here wrong. I reverted
this in r332886 because of a miscompile due to this fact.
Repository:
rC Clang
https://reviews.llvm.org/D46241
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