[clang] Look through parens around reinterpret_cast to emit a warning (#157033)

Clang warns about UB when a `reinterpret_cast` is dereferenced as an
incompatible type:
```
  long l;
  *reinterpret_cast<double*>(&l) // UB
```
However, the code was too strict and did not handle extra parens around
a `reinterpret_cast`, so the following case was not diagnosed:
```
  long l;
  *(reinterpret_cast<double*>(&l)) // UB, but no warning
```
The patch now skips ParenExpr when looking for a CXXReinterpretCastExpr
to enable a diagnostic for the second case.

Author: asavonic

clang/docs/ReleaseNotes.rst

@@ -283,6 +283,8 @@ Improvements to Clang's diagnostics
   pointers under ``-Wthread-safety-beta`` (still experimental), which reduces
   both false positives but also false negatives through more precise analysis.
 
+- Clang now looks through parenthesis for ``-Wundefined-reinterpret-cast`` diagnostic.
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/lib/Sema/SemaExpr.cpp

@@ -14784,7 +14784,7 @@ static QualType CheckIndirectionOperand(Sema &S, Expr *Op, ExprValueKind &VK,
   QualType OpTy = Op->getType();
   QualType Result;
 
-  if (isa<CXXReinterpretCastExpr>(Op)) {
+  if (isa<CXXReinterpretCastExpr>(Op->IgnoreParens())) {
     QualType OpOrigType = Op->IgnoreParenCasts()->getType();
     S.CheckCompatibleReinterpretCast(OpOrigType, OpTy, /*IsDereference*/true,
                                      Op->getSourceRange());

clang/test/SemaCXX/reinterpret-cast.cpp

@@ -167,6 +167,10 @@ void dereference_reinterpret_cast() {
   (void)reinterpret_cast<float&>(d);  // expected-warning {{reinterpret_cast from 'double' to 'float &' has undefined behavior}}
   (void)*reinterpret_cast<float*>(&d);  // expected-warning {{dereference of type 'float *' that was reinterpret_cast from type 'double *' has undefined behavior}}
 
+  // Look through parens
+  (void)*(reinterpret_cast<double*>(&l));  // expected-warning {{dereference of type 'double *' that was reinterpret_cast from type 'long *' has undefined behavior}}
+  (void)*((reinterpret_cast<double*>((&l))));  // expected-warning {{dereference of type 'double *' that was reinterpret_cast from type 'long *' has undefined behavior}}
+
   // TODO: add warning for tag types
   (void)reinterpret_cast<A&>(b);
   (void)*reinterpret_cast<A*>(&b);