[clang] [Safe Buffers] Fix a small bug recently found (PR #102953)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-analysis

Author: Ziqing Luo (ziqingluo-90)

<details>
<summary>Changes</summary>

`QualType::isConstantArrayType()` checks canonical type. So a following cast should be applied to canonical type as well:

```
if (Ty->isConstantArrayType())
  cast<ConstantArrayType>(Ty.getCanonicalType());  //  cast<ConstantArrayType>(Ty) is incorrect
```

---
Full diff: https://github.com/llvm/llvm-project/pull/102953.diff


2 Files Affected:

- (modified) clang/lib/Analysis/UnsafeBufferUsage.cpp (+1-1) 
- (modified) clang/test/SemaCXX/warn-unsafe-buffer-usage-in-container-span-construct.cpp (+3) 


``````````diff
diff --git a/clang/lib/Analysis/UnsafeBufferUsage.cpp b/clang/lib/Analysis/UnsafeBufferUsage.cpp
index 866222380974b..379b3ea7adf9e 100644
--- a/clang/lib/Analysis/UnsafeBufferUsage.cpp
+++ b/clang/lib/Analysis/UnsafeBufferUsage.cpp
@@ -404,7 +404,7 @@ AST_MATCHER(CXXConstructExpr, isSafeSpanTwoParamConstruct) {
 
   if (Arg0Ty->isConstantArrayType()) {
     const APSInt ConstArrSize =
-        APSInt(cast<ConstantArrayType>(Arg0Ty)->getSize());
+        APSInt(cast<ConstantArrayType>(Arg0Ty.getCanonicalType())->getSize());
 
     // Check form 4:
     return Arg1CV && APSInt::compareValues(ConstArrSize, *Arg1CV) == 0;
diff --git a/clang/test/SemaCXX/warn-unsafe-buffer-usage-in-container-span-construct.cpp b/clang/test/SemaCXX/warn-unsafe-buffer-usage-in-container-span-construct.cpp
index a1ddc384e0d9b..f4f2a028f0b8f 100644
--- a/clang/test/SemaCXX/warn-unsafe-buffer-usage-in-container-span-construct.cpp
+++ b/clang/test/SemaCXX/warn-unsafe-buffer-usage-in-container-span-construct.cpp
@@ -79,6 +79,8 @@ namespace construct_wt_ptr_size {
     unsigned Y = 10;
     std::span<int> S = std::span{&X, 1}; // no-warning
     int Arr[10];
+    typedef int TenInts_t[10];
+    TenInts_t Arr2;
 
     S = std::span{&X, 2};                // expected-warning{{the two-parameter std::span construction is unsafe as it can introduce mismatch between buffer size and the bound information}}
     S = std::span{new int[10], 10};      // no-warning
@@ -90,6 +92,7 @@ namespace construct_wt_ptr_size {
     S = std::span{new int[10], 9};       // expected-warning{{the two-parameter std::span construction is unsafe as it can introduce mismatch between buffer size and the bound information}}  // not smart enough to tell its safe
     S = std::span{new int[10], Y};       // expected-warning{{the two-parameter std::span construction is unsafe as it can introduce mismatch between buffer size and the bound information}}  // not smart enough to tell its safe
     S = std::span{Arr, 10};              // no-warning
+    S = std::span{Arr2, 10};             // no-warning    
     S = std::span{Arr, Y};               // expected-warning{{the two-parameter std::span construction is unsafe as it can introduce mismatch between buffer size and the bound information}}  // not smart enough to tell its safe
     S = std::span{p, 0};                 // no-warning
   }

``````````

</details>


https://github.com/llvm/llvm-project/pull/102953