[clang] [CIR] Add if statement support (PR #134333)

[Andy Kaylor via cfe-commits]

================
@@ -135,6 +135,55 @@ mlir::Location CIRGenFunction::getLoc(mlir::Location lhs, mlir::Location rhs) {
   return mlir::FusedLoc::get(locs, metadata, &getMLIRContext());
 }
 
+bool CIRGenFunction::containsLabel(const Stmt *s, bool ignoreCaseStmts) {
+  // Null statement, not a label!
+  if (!s)
+    return false;
+
+  // If this is a label, we have to emit the code, consider something like:
+  // if (0) {  ...  foo:  bar(); }  goto foo;
+  //
+  // TODO: If anyone cared, we could track __label__'s, since we know that you
+  // can't jump to one from outside their declared region.
+  if (isa<LabelStmt>(s))
+    return true;
+
+  // If this is a case/default statement, and we haven't seen a switch, we
+  // have to emit the code.
+  if (isa<SwitchCase>(s) && !ignoreCaseStmts)
+    return true;
+
+  // If this is a switch statement, we want to ignore cases below it.
----------------
andykaylor wrote:

```suggestion
  // If this is a switch statement, we want to ignore case statements when we
  // recursively process the sub-statements of the switch. If we haven't
  // encountered a switch statement, we treat case statements like labels, but
  // if we are processing a switch statement, case statements are expected.
```
This is intended to capture the outcome of the discussion below.


https://github.com/llvm/llvm-project/pull/134333