[clang] [clang] Implement -Walloc-size diagnostic option (PR #150028)

[Aaron Ballman via cfe-commits]

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@@ -7818,6 +7819,35 @@ ExprResult Sema::CheckExtVectorCast(SourceRange R, QualType DestTy,
   return prepareVectorSplat(DestTy, CastExpr);
 }
 
+/// Check that a call to alloc_size function specifies sufficient space for the
+/// destination type.
+static void CheckSufficientAllocSize(Sema &S, QualType DestType,
+                                     const Expr *E) {
+  QualType SourceType = E->getType();
+  if (!DestType->isPointerType() || !SourceType->isPointerType() ||
+      DestType == SourceType)
+    return;
+
+  const auto *CE = dyn_cast<CallExpr>(E->IgnoreCasts());
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AaronBallman wrote:

I think we want `IgnoreParenImpCasts()`? We probably should not ignore *all* casts because the user could be doing something funky like explicitly casting a function pointer type.

https://github.com/llvm/llvm-project/pull/150028