[PATCH] D65361: [analyzer] Trust global initializers when analyzing main().

[Artem Dergachev via Phabricator via cfe-commits]

NoQ created this revision.
NoQ added reviewers: dcoughlin, xazax.hun, a_sidorin, rnkovacs, Szelethus, baloghadamsoftware, Charusso.
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Herald added a project: clang.

This is inspired by https://bugs.llvm.org/show_bug.cgi?id=42780, even though it doesn't fix the bug.

If the global variable has an initializer, we'll ignore it because we're normally not analyzing the program from the beginning. This means that a global variable may have changed before we start our analysis.

However when we're analyzing main() as the top-level function, we can rely on global initializers to still be valid. At least in C; in C++ we have global constructors for breaking this logic. In C we can also have global constructors as a GNU extension, but i'd rather not worry about that.

In this patch i don't try to evaluate global initializers; the patch only covers the case when they're constants. This is the reason why we don't cover https://bugs.llvm.org/show_bug.cgi?id=42780, however we could cover it if `SValBuilder.getConstantVal()` was a bit more feature-rich (namely, we need to be able to constant-evaluate expressions like `&var.field` where `var` is a global variable; it's a concrete region (i.e., without symbolic base) value in our model, so we can make `getConstantVal()` powerful enough to emit it).

For initializers of fields and elements i'm piggybacking on @r.stahl's work to cover global constant initializers (D45774 <https://reviews.llvm.org/D45774>).

The main benefit of this patch is to make it harder for people to send us false positive reproducers that don't actually reproduce the false positive that they're having :)


Repository:
  rC Clang

https://reviews.llvm.org/D65361

Files:
  clang/lib/StaticAnalyzer/Core/RegionStore.cpp
  clang/test/Analysis/main.c

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