[PATCH] D107636: [analyzer][solver] Compute adjustment for unsupported symbols as well

[Valeriy Savchenko via Phabricator via cfe-commits]

vsavchenko created this revision.
vsavchenko added reviewers: NoQ, xazax.hun, martong, steakhal, Szelethus, ASDenysPetrov, manas, RedDocMD.
Herald added subscribers: dkrupp, donat.nagy, mikhail.ramalho, a.sidorin, rnkovacs, szepet, baloghadamsoftware.
vsavchenko requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

When the solver sees conditions like `a +/- INT cmp INT`, it disassembles
such expressions and uses the first integer constant as a so-called "Adjustment".
So it's easier later on to reason about the range of the symbol (`a`
in this case).

However, conditions of form `a +/- INT` are not treated the same way,
and we might end up with contradictory constraints.

This patch resolves this issue and extracts "Adjustment" for the
latter case as well.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D107636

Files:
  clang/lib/StaticAnalyzer/Core/RangedConstraintManager.cpp
  clang/test/Analysis/infeasible_paths.c


Index: clang/test/Analysis/infeasible_paths.c
===================================================================
--- /dev/null
+++ clang/test/Analysis/infeasible_paths.c
@@ -0,0 +1,25 @@
+// RUN: %clang_analyze_cc1 -analyzer-checker=core,debug.ExprInspection -verify %s
+
+// expected-no-diagnostics
+
+void clang_analyzer_warnIfReached();
+
+void unsupportedSymAssumption_1(int a) {
+  int b = a + 1;
+  if (b + 1)
+    return;
+  // At this point, b == -1, a == -2
+  // and this condition is always true.
+  if (b < 1)
+    return;
+  clang_analyzer_warnIfReached(); // no-warning
+}
+
+void unsupportedSymAssumption_2(int a) {
+  int b = a - 1;
+  if (!b)
+    return;
+  if (b)
+    return;
+  clang_analyzer_warnIfReached(); // no-warning
+}
Index: clang/lib/StaticAnalyzer/Core/RangedConstraintManager.cpp
===================================================================
--- clang/lib/StaticAnalyzer/Core/RangedConstraintManager.cpp
+++ clang/lib/StaticAnalyzer/Core/RangedConstraintManager.cpp
@@ -137,10 +137,13 @@
 
   // Reverse the operation and add directly to state.
   const llvm::APSInt &Zero = BVF.getValue(0, T);
+  llvm::APSInt Adjustment = Zero;
+  computeAdjustment(Sym, Adjustment);
+
   if (Assumption)
-    return assumeSymNE(State, Sym, Zero, Zero);
-  else
-    return assumeSymEQ(State, Sym, Zero, Zero);
+    return assumeSymNE(State, Sym, Zero, Adjustment);
+
+  return assumeSymEQ(State, Sym, Zero, Adjustment);
 }
 
 ProgramStateRef RangedConstraintManager::assumeSymRel(ProgramStateRef State,


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D107636.364750.patch
Type: text/x-patch
Size: 1529 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20210806/b535ddfb/attachment.bin>