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

[Andy Kaylor via cfe-commits]

================
@@ -316,6 +316,106 @@ void CIRGenFunction::emitIgnoredExpr(const Expr *e) {
   emitLValue(e);
 }
 
+/// Emit an `if` on a boolean condition, filling `then` and `else` into
+/// appropriated regions.
+mlir::LogicalResult CIRGenFunction::emitIfOnBoolExpr(const Expr *cond,
+                                                     const Stmt *thenS,
+                                                     const Stmt *elseS) {
+  // Attempt to be more accurate as possible with IfOp location, generate
+  // one fused location that has either 2 or 4 total locations, depending
+  // on else's availability.
+  auto getStmtLoc = [this](const Stmt &s) {
+    return mlir::FusedLoc::get(&getMLIRContext(),
+                               {getLoc(s.getSourceRange().getBegin()),
+                                getLoc(s.getSourceRange().getEnd())});
+  };
+  mlir::Location thenLoc = getStmtLoc(*thenS);
----------------
andykaylor wrote:

```suggestion
  mlir::Location thenLoc = getLoc(thenS->getSourceRange());
```
Also, it would be good to assert that `thenS` isn't null before dereferencing it here.

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