[clang] [analyzer] Fix zext assertion failure in loop unrolling (PR #121203)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

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

Author: JOSTAR (shenjunjiekoda)

<details>
<summary>Changes</summary>

The current implementation of APInt extension in the code can trigger an assertion failure when the `zext` function is called with a target width smaller than the current bit width. For example:
```cpp
if (InitNum.getBitWidth() != BoundNum.getBitWidth()) {
    InitNum = InitNum.zext(BoundNum.getBitWidth());
    BoundNum = BoundNum.zext(InitNum.getBitWidth());
}
```

This logic does not guarantee that the `zext` target width is always greater than or equal to the current bit width, leading to potential crashes.

Expected Behavior:
- Ensure InitNum and BoundNum are extended to the maximum of their respective widths.
- Prevent assertion failures by enforcing correct `zext` usage.

Depend on ##<!-- -->121201

---
Full diff: https://github.com/llvm/llvm-project/pull/121203.diff


1 Files Affected:

- (modified) clang/lib/StaticAnalyzer/Core/LoopUnrolling.cpp (+6-4) 


``````````diff
diff --git a/clang/lib/StaticAnalyzer/Core/LoopUnrolling.cpp b/clang/lib/StaticAnalyzer/Core/LoopUnrolling.cpp
index 96f5d7c44baf89..e3b27e22712b58 100644
--- a/clang/lib/StaticAnalyzer/Core/LoopUnrolling.cpp
+++ b/clang/lib/StaticAnalyzer/Core/LoopUnrolling.cpp
@@ -283,10 +283,12 @@ static bool shouldCompletelyUnroll(const Stmt *LoopStmt, ASTContext &ASTCtx,
   llvm::APInt InitNum =
       Matches[0].getNodeAs<IntegerLiteral>("initNum")->getValue();
   auto CondOp = Matches[0].getNodeAs<BinaryOperator>("conditionOperator");
-  if (InitNum.getBitWidth() != BoundNum.getBitWidth()) {
-    InitNum = InitNum.zext(BoundNum.getBitWidth());
-    BoundNum = BoundNum.zext(InitNum.getBitWidth());
-  }
+  unsigned MaxWidth = std::max(InitNum.getBitWidth(), BoundNum.getBitWidth());
+
+  if (InitNum.getBitWidth() != MaxWidth)
+      InitNum = InitNum.zext(MaxWidth);
+  if (BoundNum.getBitWidth() != MaxWidth)
+      BoundNum = BoundNum.zext(MaxWidth);
 
   if (CondOp->getOpcode() == BO_GE || CondOp->getOpcode() == BO_LE)
     maxStep = (BoundNum - InitNum + 1).abs().getZExtValue();

``````````

</details>


https://github.com/llvm/llvm-project/pull/121203