[PATCH] D81061: [Analyzer][VLASizeChecker] Fix problem with zero index assumption.

[Balázs Kéri via Phabricator via cfe-commits]

balazske updated this revision to Diff 268216.
balazske added a comment.

Improved assumption on array size.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D81061/new/

https://reviews.llvm.org/D81061

Files:
  clang/lib/StaticAnalyzer/Checkers/VLASizeChecker.cpp
  clang/test/Analysis/vla.c


Index: clang/test/Analysis/vla.c
===================================================================
--- clang/test/Analysis/vla.c
+++ clang/test/Analysis/vla.c
@@ -137,3 +137,17 @@
   clang_analyzer_eval(clang_analyzer_getExtent(&vla3m) == 2 * x * 4 * sizeof(int));
   // expected-warning at -1{{TRUE}}
 }
+
+// https://bugs.llvm.org/show_bug.cgi?id=46128
+// Analyzer doesn't handle more than simple symbolic expressions correct.
+// Just don't crash.
+extern void foo(void);
+int a;
+void b() {
+  int c = a + 1;
+  for (;;) {
+    int d[c];
+    for (; 0 < c;)
+      foo();
+  }
+} // no-crash
Index: clang/lib/StaticAnalyzer/Checkers/VLASizeChecker.cpp
===================================================================
--- clang/lib/StaticAnalyzer/Checkers/VLASizeChecker.cpp
+++ clang/lib/StaticAnalyzer/Checkers/VLASizeChecker.cpp
@@ -122,11 +122,19 @@
       return State;
 
     if (const llvm::APSInt *IndexLVal = SVB.getKnownValue(State, IndexLength)) {
+      uint64_t IndexL = IndexLVal->getZExtValue();
+      if (IndexL == 0) {
+        // Despite the previous assumption for positive size,
+        // this value might be non-positive (probably caused by other bugs).
+        // At least check for zero again.
+        // Assume that this is a more exact fact than the previous assumptions
+        // (in checkVLAIndexSize), so report error too.
+        reportBug(VLA_Zero, SizeE, State, C);
+        return nullptr;
+      }
       // Check if the array size will overflow.
       // Size overflow check does not work with symbolic expressions because a
       // overflow situation can not be detected easily.
-      uint64_t IndexL = IndexLVal->getZExtValue();
-      assert(IndexL > 0 && "Index length should have been checked for zero.");
       if (KnownSize <= SizeMax / IndexL) {
         KnownSize *= IndexL;
       } else {
@@ -166,35 +174,21 @@
     return nullptr;
   }
 
-  // Check if the size is zero.
+  QualType SizeTy = SizeE->getType();
   DefinedSVal SizeD = SizeV.castAs<DefinedSVal>();
-
-  ProgramStateRef StateNotZero, StateZero;
-  std::tie(StateNotZero, StateZero) = State->assume(SizeD);
-
-  if (StateZero && !StateNotZero) {
-    reportBug(VLA_Zero, SizeE, StateZero, C);
-    return nullptr;
-  }
-
-  // From this point on, assume that the size is not zero.
-  State = StateNotZero;
-
-  // Check if the size is negative.
   SValBuilder &SVB = C.getSValBuilder();
-
-  QualType SizeTy = SizeE->getType();
   DefinedOrUnknownSVal Zero = SVB.makeZeroVal(SizeTy);
 
-  SVal LessThanZeroVal = SVB.evalBinOp(State, BO_LT, SizeD, Zero, SizeTy);
-  if (Optional<DefinedSVal> LessThanZeroDVal =
-          LessThanZeroVal.getAs<DefinedSVal>()) {
-    ConstraintManager &CM = C.getConstraintManager();
-    ProgramStateRef StatePos, StateNeg;
+  // Check if the size is zero or negative.
+  SVal PositiveVal = SVB.evalBinOp(State, BO_GT, SizeD, Zero, SizeTy);
+  if (Optional<DefinedSVal> PositiveDVal = PositiveVal.getAs<DefinedSVal>()) {
+    ProgramStateRef StatePos, StateNotPos;
 
-    std::tie(StateNeg, StatePos) = CM.assumeDual(State, *LessThanZeroDVal);
-    if (StateNeg && !StatePos) {
-      reportBug(VLA_Negative, SizeE, State, C);
+    std::tie(StatePos, StateNotPos) = State->assume(*PositiveDVal);
+    if (StateNotPos && !StatePos) {
+      ConditionTruthVal IsZeroSize = StateNotPos->isNull(SizeD);
+      reportBug(IsZeroSize.isConstrainedTrue() ? VLA_Zero : VLA_Negative, SizeE,
+                State, C);
       return nullptr;
     }
     State = StatePos;


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