[PATCH] D130811: [Clang] Fix handling of Max from getValueRange(...) in IntExprEvaluator::VisitCastExpr(...)

Erich Keane via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Tue Aug 2 11:40:27 PDT 2022

erichkeane added inline comments.

Comment at: clang/lib/AST/ExprConstant.cpp:13540
         ED->getValueRange(Max, Min);
+        --Max;
shafik wrote:
> erichkeane wrote:
> > I don't think this is the correct answer.  Even though the other use of this seems to 'work', `getValueRange` is still returning wrapped values here.  The fix is to figure out how to fix the math in getValueRange, and change the sanitizer's IR generation if necessary.
> So the other user of these values is `getRangeForLoadFromType(...)` through `getRangeForType(...)` which is used to generate the [range metadata](https://llvm.org/docs/LangRef.html#range-metadata) and in this case the range is exclusive on the right side:
> > The pair a,b represents the range [a,b).
> and it is allowed to wrap:
> > The range is allowed to wrap.
> So I believe the behavior will be correct. 
> Even though the range looks off in this example: https://godbolt.org/z/z7d9PKoMn
> ```
> !{i32 0, i32 -2147483648}
> ```
> I think it does the right thing.
> Note the language ref also says:
> > The type must match the type loaded by the instruction.
> and a quick experiment to use `i33` confirms this breaks.
Hmm... ok.  Well, its quite unfortunate that 2 of our 3 uses of this are having to hack around this behavior a bit, but I guess this will have to be acceptable short-term then.

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