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

[Shafik Yaghmour via Phabricator via cfe-commits]

shafik added inline comments.


================
Comment at: clang/lib/AST/ExprConstant.cpp:13540
         ED->getValueRange(Max, Min);
+        --Max;
 
----------------
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.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D130811/new/

https://reviews.llvm.org/D130811