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

[via cfe-commits]

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@@ -263,6 +264,72 @@ static void terminateBody(CIRGenBuilderTy &builder, mlir::Region &r,
     b->erase();
 }
 
+mlir::LogicalResult CIRGenFunction::emitIfStmt(const IfStmt &s) {
+  mlir::LogicalResult res = mlir::success();
+  // The else branch of a consteval if statement is always the only branch
+  // that can be runtime evaluated.
+  const Stmt *ConstevalExecuted;
+  if (s.isConsteval()) {
+    ConstevalExecuted = s.isNegatedConsteval() ? s.getThen() : s.getElse();
+    if (!ConstevalExecuted) {
+      // No runtime code execution required
+      return res;
+    }
+  }
+
+  // C99 6.8.4.1: The first substatement is executed if the expression
+  // compares unequal to 0.  The condition must be a scalar type.
+  auto ifStmtBuilder = [&]() -> mlir::LogicalResult {
+    if (s.isConsteval())
+      return emitStmt(ConstevalExecuted, /*useCurrentScope=*/true);
+
+    if (s.getInit())
+      if (emitStmt(s.getInit(), /*useCurrentScope=*/true).failed())
+        return mlir::failure();
+
+    if (s.getConditionVariable())
+      emitDecl(*s.getConditionVariable());
+
+    // During LLVM codegen, if the condition constant folds and can be elided,
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Andres-Salamanca wrote:

Changes applied Let me know if it looks good now

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