[clang] [analyzer] Fix assertion failure in CXXInstanceCall::getCXXThisVal (PR #70837)

[Balazs Benics via cfe-commits]

https://github.com/steakhal updated https://github.com/llvm/llvm-project/pull/70837

>From a7f64815f4986fad597b9cb2d1acce2de9ac20bf Mon Sep 17 00:00:00 2001
From: Balazs Benics <benicsbalazs at gmail.com>
Date: Mon, 23 Oct 2023 18:10:29 +0200
Subject: [PATCH 1/2] [analyzer] Fix assertion failure in
 CXXInstanceCall::getCXXThisVal

Workaround the case when the `this` pointer is actually a `NonLoc`, by
returning `Unknown` instead.
The solution isn't ideal, as `this` should be really a `Loc`, but due to
how casts work, I feel this is our easiest and best option.

I've considered using `SVB.evalCast(ThisVal, Base->getType(), QualType())`,
but it doesn't work as `EvalCastVisitor::VisitNonLocSymbolVal()` only
evaluates casts that happen from NonLoc to NonLocs.

When I tried to actually implement that case, I figured:
1) Create a SymbolicRegion from that nonloc::SymbolVal; but SymbolRegion
   ctor expects a pointer type for the symbol.
2) Okay, just have a SymbolCast, getting us the pointer type; but
   SymbolRegion expects SymbolData symbols, not generic SymExprs, as stated:

> // Because pointer arithmetic is represented by ElementRegion layers,
> // the base symbol here should not contain any arithmetic.

3) We can't use ElementRegions to perform this cast because to have an
   ElementRegion, you already have to have a SubRegion that you want to
   cast, but the point is that we don't have that.

At this point, I gave up, and just returned `Unknown` xD
IMO this is still better than having a crash.

Fixes #69922
---
 clang/lib/StaticAnalyzer/Core/CallEvent.cpp |  5 ++---
 clang/test/Analysis/builtin_bitcast.cpp     | 21 +++++++++++++++++++++
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/clang/lib/StaticAnalyzer/Core/CallEvent.cpp b/clang/lib/StaticAnalyzer/Core/CallEvent.cpp
index ad5bb66c4fff3c8..20bc64dc2631cec 100644
--- a/clang/lib/StaticAnalyzer/Core/CallEvent.cpp
+++ b/clang/lib/StaticAnalyzer/Core/CallEvent.cpp
@@ -715,10 +715,9 @@ void CXXInstanceCall::getExtraInvalidatedValues(
 SVal CXXInstanceCall::getCXXThisVal() const {
   const Expr *Base = getCXXThisExpr();
   // FIXME: This doesn't handle an overloaded ->* operator.
-  if (!Base)
+  SVal ThisVal = Base ? getSVal(Base) : UnknownVal();
+  if (isa<NonLoc>(ThisVal))
     return UnknownVal();
-
-  SVal ThisVal = getSVal(Base);
   assert(ThisVal.isUnknownOrUndef() || isa<Loc>(ThisVal));
   return ThisVal;
 }
diff --git a/clang/test/Analysis/builtin_bitcast.cpp b/clang/test/Analysis/builtin_bitcast.cpp
index 396e7caa45f6acd..13475694d287a22 100644
--- a/clang/test/Analysis/builtin_bitcast.cpp
+++ b/clang/test/Analysis/builtin_bitcast.cpp
@@ -30,3 +30,24 @@ void test(int i) {
   clang_analyzer_dump(g4);
   // expected-warning at -1 {{&i [as 64 bit integer]}}
 }
+
+struct A {
+  int n;
+  void set(int x) {
+    n = x;
+  }
+};
+using ptr_size = decltype(sizeof(void *));
+void gh_69922(ptr_size p) {
+  // expected-warning-re at +1 {{(reg_${{[0-9]+}}<ptr_size p>) & 1U}}
+  clang_analyzer_dump(__builtin_bit_cast(A*, p & 1));
+
+  __builtin_bit_cast(A*, p & 1)->set(2); // no-crash
+  // However, since the `this` pointer is expected to be a Loc, but we have
+  // NonLoc there, we simply give up and resolve it as `Unknown`.
+  // Then, inside the `set()` member function call we can't evaluate the
+  // store to the member variable `n`.
+
+  clang_analyzer_dump(__builtin_bit_cast(A*, p & 1)->n); // Ideally, this should print "2".
+  // expected-warning-re at -1 {{(reg_${{[0-9]+}}<ptr_size p>) & 1U}}
+}

>From 27d2b84e14d73dcc2385f202a204993f25235de4 Mon Sep 17 00:00:00 2001
From: Balazs Benics <benicsbalazs at gmail.com>
Date: Tue, 31 Oct 2023 19:20:16 +0100
Subject: [PATCH 2/2] Add fixme and add the ineffective evalCast

---
 clang/lib/StaticAnalyzer/Core/CallEvent.cpp   | 9 +++++++--
 clang/lib/StaticAnalyzer/Core/SValBuilder.cpp | 5 +++++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/clang/lib/StaticAnalyzer/Core/CallEvent.cpp b/clang/lib/StaticAnalyzer/Core/CallEvent.cpp
index 20bc64dc2631cec..76fb7481f65194b 100644
--- a/clang/lib/StaticAnalyzer/Core/CallEvent.cpp
+++ b/clang/lib/StaticAnalyzer/Core/CallEvent.cpp
@@ -716,8 +716,13 @@ SVal CXXInstanceCall::getCXXThisVal() const {
   const Expr *Base = getCXXThisExpr();
   // FIXME: This doesn't handle an overloaded ->* operator.
   SVal ThisVal = Base ? getSVal(Base) : UnknownVal();
-  if (isa<NonLoc>(ThisVal))
-    return UnknownVal();
+
+  if (isa<NonLoc>(ThisVal)) {
+    SValBuilder &SVB = getState()->getStateManager().getSValBuilder();
+    QualType OriginalTy = ThisVal.getType(SVB.getContext());
+    return SVB.evalCast(ThisVal, Base->getType(), OriginalTy);
+  }
+
   assert(ThisVal.isUnknownOrUndef() || isa<Loc>(ThisVal));
   return ThisVal;
 }
diff --git a/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp b/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp
index d89d82626f72694..9375f39b2d71dd4 100644
--- a/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp
+++ b/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp
@@ -980,6 +980,11 @@ class EvalCastVisitor : public SValVisitor<EvalCastVisitor, SVal> {
           return VB.makeNonLoc(SE, T, CastTy);
     }
 
+    // FIXME: We should be able to cast NonLoc -> Loc
+    // (when Loc::isLocType(CastTy) is true)
+    // But it's hard to do as SymbolicRegions can't refer to SymbolCasts holding
+    // generic SymExprs. Check the commit message for the details.
+
     // Symbol to pointer and whatever else.
     return UnknownVal();
   }