[clang] [clang][analyzer] Extend lifetime of dynamic extent information (PR #163562)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

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

Author: Balázs Kéri (balazske)

<details>
<summary>Changes</summary>

Symbols used for dynamic extent information of memory regions are now kept as live as long as the memory region exists.

---
Full diff: https://github.com/llvm/llvm-project/pull/163562.diff


4 Files Affected:

- (modified) clang/include/clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h (+2) 
- (modified) clang/lib/StaticAnalyzer/Core/DynamicExtent.cpp (+6) 
- (modified) clang/lib/StaticAnalyzer/Core/ExprEngine.cpp (+2) 
- (modified) clang/test/Analysis/ArrayBound/verbose-tests.c (-18) 


``````````diff
diff --git a/clang/include/clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h b/clang/include/clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h
index 1a9bef06b15a4..440603fb4d8c7 100644
--- a/clang/include/clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h
+++ b/clang/include/clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h
@@ -58,6 +58,8 @@ SVal getDynamicExtentWithOffset(ProgramStateRef State, SVal BufV);
 DefinedOrUnknownSVal getDynamicElementCountWithOffset(ProgramStateRef State,
                                                       SVal BufV, QualType Ty);
 
+void markAllDynamicExtentLive(ProgramStateRef State, SymbolReaper &SymReaper);
+
 } // namespace ento
 } // namespace clang
 
diff --git a/clang/lib/StaticAnalyzer/Core/DynamicExtent.cpp b/clang/lib/StaticAnalyzer/Core/DynamicExtent.cpp
index 34078dbce0b68..e436b186a2148 100644
--- a/clang/lib/StaticAnalyzer/Core/DynamicExtent.cpp
+++ b/clang/lib/StaticAnalyzer/Core/DynamicExtent.cpp
@@ -128,5 +128,11 @@ ProgramStateRef setDynamicExtent(ProgramStateRef State, const MemRegion *MR,
   return State->set<DynamicExtentMap>(MR->StripCasts(), Size);
 }
 
+void markAllDynamicExtentLive(ProgramStateRef State, SymbolReaper &SymReaper) {
+  for (const auto &I : State->get<DynamicExtentMap>())
+    if (SymbolRef Sym = I.second.getAsSymbol())
+      SymReaper.markLive(Sym);
+}
+
 } // namespace ento
 } // namespace clang
diff --git a/clang/lib/StaticAnalyzer/Core/ExprEngine.cpp b/clang/lib/StaticAnalyzer/Core/ExprEngine.cpp
index 785cdfa15bf04..d9ddc12c54985 100644
--- a/clang/lib/StaticAnalyzer/Core/ExprEngine.cpp
+++ b/clang/lib/StaticAnalyzer/Core/ExprEngine.cpp
@@ -1064,6 +1064,8 @@ void ExprEngine::removeDead(ExplodedNode *Pred, ExplodedNodeSet &Out,
       SymReaper.markLive(MR);
   }
 
+  markAllDynamicExtentLive(CleanedState, SymReaper);
+
   getCheckerManager().runCheckersForLiveSymbols(CleanedState, SymReaper);
 
   // Create a state in which dead bindings are removed from the environment
diff --git a/clang/test/Analysis/ArrayBound/verbose-tests.c b/clang/test/Analysis/ArrayBound/verbose-tests.c
index e3416886d13e5..9ee290ab6b5b8 100644
--- a/clang/test/Analysis/ArrayBound/verbose-tests.c
+++ b/clang/test/Analysis/ArrayBound/verbose-tests.c
@@ -381,30 +381,12 @@ int *symbolicExtent(int arg) {
     return 0;
   int *mem = (int*)malloc(arg);
 
-  // TODO: without the following reference to 'arg', the analyzer would discard
-  // the range information about (the symbolic value of) 'arg'. This is
-  // incorrect because while the variable itself is inaccessible, it becomes
-  // the symbolic extent of 'mem', so we still want to reason about its
-  // potential values.
-  (void)arg;
-
   mem[8] = -2;
   // expected-warning at -1 {{Out of bound access to memory after the end of the heap area}}
   // expected-note at -2 {{Access of 'int' element in the heap area at index 8}}
   return mem;
 }
 
-int *symbolicExtentDiscardedRangeInfo(int arg) {
-  // This is a copy of the case 'symbolicExtent' without the '(void)arg' hack.
-  // TODO: if the analyzer can detect the out-of-bounds access within this
-  // testcase, then remove this and the `(void)arg` hack from `symbolicExtent`.
-  if (arg >= 5)
-    return 0;
-  int *mem = (int*)malloc(arg);
-  mem[8] = -2;
-  return mem;
-}
-
 void symbolicIndex(int arg) {
   // expected-note at +2 {{Assuming 'arg' is >= 12}}
   // expected-note at +1 {{Taking true branch}}

``````````

</details>


https://github.com/llvm/llvm-project/pull/163562