[clang] [analyzer] Suppress out of bounds reports after weak loop assumptions (PR #109804)

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=?utf-8?q?Donát?= Nagy <donat.nagy at ericsson.com>,
=?utf-8?q?Donát?= Nagy <donat.nagy at ericsson.com>,
=?utf-8?q?Donát?= Nagy <donat.nagy at ericsson.com>,
=?utf-8?q?Donát?= Nagy <donat.nagy at ericsson.com>,
=?utf-8?q?Donát?= Nagy <donat.nagy at ericsson.com>,
=?utf-8?q?Donát?= Nagy <donat.nagy at ericsson.com>
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In-Reply-To: <llvm.org/llvm/llvm-project/pull/109804 at github.com>


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@@ -441,10 +441,32 @@ void CoreEngine::HandleCallEnter(const CallEnter &CE, ExplodedNode *Pred) {
 void CoreEngine::HandleBranch(const Stmt *Cond, const Stmt *Term,
                                 const CFGBlock * B, ExplodedNode *Pred) {
   assert(B->succ_size() == 2);
+
+  const LocationContext *LC = Pred->getLocationContext();
+  BlockCounter Counter = WList->getBlockCounter();
+  unsigned BlockCount =
+      Counter.getNumVisited(LC->getStackFrame(), B->getBlockID());
+  std::optional<unsigned> IterationsFinishedInLoop = std::nullopt;
+  if (isa<ForStmt, WhileStmt, CXXForRangeStmt>(Term)) {
+    // FIXME: This code approximates the number of finished iterations based on
+    // the block count, i.e. the number of evaluations of the terminator block
+    // on the current execution path (which includes the current evaluation, so
+    // is always >= 1). This is probably acceptable for the checker-specific
+    // false positive suppression that currently uses this value, but it would
+    // be better to calcuate an accurate count of iterations.
+    assert(BlockCount >= 1);
+    IterationsFinishedInLoop = BlockCount - 1;
+  } else if (isa<DoStmt>(Term)) {
+    // FIXME: The fixme note in the previous branch also applies here.
+    // In a do-while loop one iteration happens before the first evaluation of
+    // the loop condition, so we don't subtract one from the block count.
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isuckatcs wrote:

I just realised, we already talked about this in a previous comment.

https://github.com/llvm/llvm-project/pull/109804