[clang] [analyzer][NFC] Clean up `MemRegion.cpp` and align with llvm coding style (PR #218860)

[Balázs Benics via cfe-commits]

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@@ -207,22 +207,23 @@ QualType ParamVarRegion::getValueType() const {
 
 const ParmVarDecl *ParamVarRegion::getDecl() const {
   const Decl *D = getStackFrame()->getDecl();
-
   if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
     assert(Index < FD->param_size());
     return FD->parameters()[Index];
-  } else if (const auto *BD = dyn_cast<BlockDecl>(D)) {
+  }
+  if (const auto *BD = dyn_cast<BlockDecl>(D)) {
     assert(Index < BD->param_size());
     return BD->parameters()[Index];
-  } else if (const auto *MD = dyn_cast<ObjCMethodDecl>(D)) {
+  }
+  if (const auto *MD = dyn_cast<ObjCMethodDecl>(D)) {
     assert(Index < MD->param_size());
     return MD->parameters()[Index];
-  } else if (const auto *CD = dyn_cast<CXXConstructorDecl>(D)) {
+  }
+  if (const auto *CD = dyn_cast<CXXConstructorDecl>(D)) {
     assert(Index < CD->param_size());
     return CD->parameters()[Index];
-  } else {
-    llvm_unreachable("Unexpected Decl kind!");
   }
+  llvm_unreachable("Unexpected Decl kind!");
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steakhal wrote:

These I get it. Objectively better.

https://github.com/llvm/llvm-project/pull/218860