[clang][analyzer] Correct SMT Layer for _BitInt cases refutations

[vabridgers]

Since _BitInt was added later, ASTContext did not comprehend getting a type by bitwidth that's not a power of 2, and the SMT layer also did not comprehend this. This led to unexpected crashes using Z3 refutation during randomized testing. The assertion and redacted and summarized crash stack is shown here.

clang: ../../clang/include/clang/StaticAnalyzer/Core/PathSensitive/SMTConv.h:103:
static llvm::SMTExprRef clang::ento::SMTConv::fromBinOp(llvm::SMTSolverRef &,
const llvm::SMTExprRef &, const BinaryOperator::Opcode, const llvm::SMTExprRef &, bool):
Assertion `*Solver->getSort(LHS) == *Solver->getSort(RHS) && "AST's must have the same sort!"' failed.
...

clang::ento::SMTConv::fromBinOp(std::shared_ptr&, llvm::SMTExpr const* const&, clang::BinaryOperatorKind, llvm::SMTExpr const* const&, bool) SMTConstraintManager.cpp clang::ASTContext&, llvm::SMTExpr const* const&, clang::QualType, clang::BinaryOperatorKind, llvm::SMTExpr const* const&, clang::QualType, clang::QualType*) SMTConstraintManager.cpp clang::ASTContext&, clang::ento::SymExpr const*, llvm::APSInt const&, llvm::APSInt const&, bool) SMTConstraintManager.cpp clang::ento::ExplodedNode const*, clang::ento::PathSensitiveBugReport&)

[llvmbot]

@llvm/pr-subscribers-clang-static-analyzer-1

@llvm/pr-subscribers-clang

Author: None (vabridgers)

Changes

Since _BitInt was added later, ASTContext did not comprehend getting a type by bitwidth that's not a power of 2, and the SMT layer also did not comprehend this. This led to unexpected crashes using Z3 refutation during randomized testing. The assertion and redacted and summarized crash stack is shown here.

clang: ../../clang/include/clang/StaticAnalyzer/Core/PathSensitive/SMTConv.h:103:
static llvm::SMTExprRef clang::ento::SMTConv::fromBinOp(llvm::SMTSolverRef &,
const llvm::SMTExprRef &, const BinaryOperator::Opcode, const llvm::SMTExprRef &, bool):
Assertion `Solver->getSort(LHS) == Solver->getSort(RHS) && "AST's must have the same sort!"' failed.
...
 #9 <address> clang::ento::SMTConv::fromBinOp(std::shared_ptr<llvm::SMTSolver>&,
llvm::SMTExpr const const&, clang::BinaryOperatorKind, llvm::SMTExpr const const&,
bool) SMTConstraintManager.cpp
clang::ASTContext&, llvm::SMTExpr const* const&, clang::QualType,
clang::BinaryOperatorKind, llvm::SMTExpr const* const&, clang::QualType,
clang::QualType*) SMTConstraintManager.cpp
clang::ASTContext&, clang::ento::SymExpr const*, llvm::APSInt const&,
llvm::APSInt const&, bool) SMTConstraintManager.cpp
clang::ento::ExplodedNode const*, clang::ento::PathSensitiveBugReport&)

---

Full diff: https://github.com/llvm/llvm-project/pull/143310.diff

3 Files Affected:

• (modified) clang/include/clang/StaticAnalyzer/Core/PathSensitive/SMTConv.h (+12-2)
• (modified) clang/lib/AST/ASTContext.cpp (+7-2)
• (added) clang/test/Analysis/bitint-z3.c (+23)

diff --git a/clang/include/clang/StaticAnalyzer/Core/PathSensitive/SMTConv.h b/clang/include/clang/StaticAnalyzer/Core/PathSensitive/SMTConv.h
index 580b49a38dc72..2a41202d46440 100644
--- a/clang/include/clang/StaticAnalyzer/Core/PathSensitive/SMTConv.h
+++ b/clang/include/clang/StaticAnalyzer/Core/PathSensitive/SMTConv.h
@@ -573,20 +573,30 @@ class SMTConv {
     return Ctx.getIntTypeForBitwidth(Int.getBitWidth(), Int.isSigned());
   }
 
+  static inline bool IsPower2(unsigned bits) {
+    return bits > 0 && (bits & (bits-1)) == 0;
+  }
+
   // Get the QualTy for the input APSInt, and fix it if it has a bitwidth of 1.
   static inline std::pair<llvm::APSInt, QualType>
   fixAPSInt(ASTContext &Ctx, const llvm::APSInt &Int) {
     llvm::APSInt NewInt;
+    unsigned APSIntBitwidth = Int.getBitWidth();
+    QualType Ty = getAPSIntType(Ctx, Int);
 
     // FIXME: This should be a cast from a 1-bit integer type to a boolean type,
     // but the former is not available in Clang. Instead, extend the APSInt
     // directly.
-    if (Int.getBitWidth() == 1 && getAPSIntType(Ctx, Int).isNull()) {
+    if (APSIntBitwidth == 1 && Ty.isNull()) {
       NewInt = Int.extend(Ctx.getTypeSize(Ctx.BoolTy));
+      Ty = getAPSIntType(Ctx, NewInt);
+    } else if ( !IsPower2(APSIntBitwidth)  && !getAPSIntType(Ctx, Int).isNull()) {
+      Ty = getAPSIntType(Ctx, Int);
+      NewInt = Int.extend( Ctx.getTypeSize(Ty));
     } else
       NewInt = Int;
 
-    return std::make_pair(NewInt, getAPSIntType(Ctx, NewInt));
+    return std::make_pair(NewInt, Ty);
   }
 
   // Perform implicit type conversion on binary symbolic expressions.
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 45f9602856840..094264813a8b3 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -13209,9 +13209,14 @@ size_t ASTContext::getSideTableAllocatedMemory() const {
 /// Returns empty type if there is no appropriate target types.
 QualType ASTContext::getIntTypeForBitwidth(unsigned DestWidth,
                                            unsigned Signed) const {
-  TargetInfo::IntType Ty = getTargetInfo().getIntTypeByWidth(DestWidth, Signed);
+  // round up to next power of 2 for _BitInt cases
+  unsigned pow2DestWidth = llvm::bit_ceil(DestWidth);
+  //if (pow2DestWidth == 4) pow2DestWidth = 8;
+  if (pow2DestWidth < 8) pow2DestWidth = 8;
+
+  TargetInfo::IntType Ty = getTargetInfo().getIntTypeByWidth(pow2DestWidth, Signed);
   CanQualType QualTy = getFromTargetType(Ty);
-  if (!QualTy && DestWidth == 128)
+  if (!QualTy && pow2DestWidth == 128)
     return Signed ? Int128Ty : UnsignedInt128Ty;
   return QualTy;
 }
diff --git a/clang/test/Analysis/bitint-z3.c b/clang/test/Analysis/bitint-z3.c
new file mode 100644
index 0000000000000..d50c93acdf117
--- /dev/null
+++ b/clang/test/Analysis/bitint-z3.c
@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -analyze -analyzer-checker=core -w -DNO_CROSSCHECK -verify %s
+// RUN: %clang_cc1 -analyze -analyzer-checker=core -w -analyzer-config crosscheck-with-z3=true -verify %s
+// REQUIRES: z3
+
+// The SMTConv layer did not comprehend _BitInt types (because this was an
+// evolved feature) and was crashing due to needed updates in 2 places.
+// Analysis is expected to find these cases using _BitInt without crashing.
+
+_BitInt(35) a;
+int b;
+void c() {
+  int d;
+  if (a)
+    b = d; // expected-warning{{Assigned value is uninitialized [core.uninitialized.Assign]}}
+}
+
+int *d;
+_BitInt(3) e;
+void f() {
+  int g;
+  d = &g;
+  e ?: 0; // expected-warning{{Address of stack memory associated with local variable 'g' is still referred to by the global variable 'd' upon returning to the caller.  This will be a dangling reference [core.StackAddressEscape]}}
+}

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[vabridgers]

Looks like the ASTContext change is impacting other LITs and is an incorrect approach for those reasons. Please have a look regardless and comment on different ways to address if appropriate. I'm thinking the real fix needs to be in the SMT layer, detecting a _BitInt type and "doing the right thing". Thank you!