[PATCH] D55875: [analyzer] pr38668: RegionStore: Do not attempt to cast loaded values of non-scalar types.

[Artem Dergachev via Phabricator via cfe-commits]

NoQ created this revision.
NoQ added reviewers: dcoughlin, xazax.hun, a_sidorin, george.karpenkov, rnkovacs, Szelethus, mikhail.ramalho, baloghadamsoftware.
Herald added subscribers: cfe-commits, dkrupp, donat.nagy, a.sidorin, szepet.

It is expected to have the same object (memory region) treated as if it has different types in different program points. Like, the object may be a union or contain a union, or a pointer to it can be reinterpreted as a pointer to a different type. The correct behavior for `RegionStore` when an object is stored as an object of type `T1` but loaded as an object of type `T2` is to store the object as if it has type `T1` but cast it to `T2` during load. This is what `CastRetrievedVal` is responsible for.

Note that the cast here is some sort of a "`reinterpret_cast`" (even in C). For instance, if you store a float and load an integer, you won't have your float rounded to an integer; instead, you will have garbage.

Therefore i propose to admit that we cannot perform the cast as long as types we're dealing with are non-trivial (neither integers, nor pointers). Our modeling would still be weird in this case when dealing with integer casts, but so is support for integer casts in general.

Of course, if the cast is not necessary (eg, `T1 == T2`), we can still load the value just fine. This trivial observation in fact improves our behavior on tests and addresses some old FIXMEs: previously we would have tried to perform the cast and fail. We should probably also teach `SValBuilder` to perform casts in this case.

Fixes https://bugs.llvm.org/show_bug.cgi?id=38668


Repository:
  rC Clang

https://reviews.llvm.org/D55875

Files:
  lib/StaticAnalyzer/Core/Store.cpp
  test/Analysis/bstring.cpp
  test/Analysis/casts.c
  test/Analysis/pointer-to-member.cpp

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