[clang] [CIR] Upstream initial support for switch statements (PR #137106)

[Andy Kaylor via cfe-commits]

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@@ -600,3 +721,99 @@ mlir::LogicalResult CIRGenFunction::emitWhileStmt(const WhileStmt &s) {
   terminateBody(builder, whileOp.getBody(), getLoc(s.getEndLoc()));
   return mlir::success();
 }
+
+mlir::LogicalResult CIRGenFunction::emitSwitchBody(const Stmt *s) {
+  // It is rare but legal if the switch body is not a compound stmt. e.g.,
+  //
+  //  switch(a)
+  //    while(...) {
+  //      case1
+  //      ...
+  //      case2
+  //      ...
+  //    }
+  if (!isa<CompoundStmt>(s))
+    return emitStmt(s, /*useCurrentScope=*/true);
+
+  auto *compoundStmt = cast<CompoundStmt>(s);
+
+  mlir::Block *swtichBlock = builder.getBlock();
+  for (auto *c : compoundStmt->body()) {
+    if (auto *switchCase = dyn_cast<SwitchCase>(c)) {
+      builder.setInsertionPointToEnd(swtichBlock);
+      // Reset insert point automatically, so that we can attach following
+      // random stmt to the region of previous built case op to try to make
+      // the being generated `cir.switch` to be in simple form.
+      if (mlir::failed(
+              emitSwitchCase(*switchCase, /*buildingTopLevelCase=*/true)))
+        return mlir::failure();
+
+      continue;
+    }
+
+    // Otherwise, just build the statements in the nearest case region.
+    if (mlir::failed(emitStmt(c, /*useCurrentScope=*/!isa<CompoundStmt>(c))))
+      return mlir::failure();
+  }
+
+  return mlir::success();
+}
+
+mlir::LogicalResult CIRGenFunction::emitSwitchStmt(const clang::SwitchStmt &s) {
+  // TODO: LLVM codegen does some early optimization to fold the condition and
+  // only emit live cases. CIR should use MLIR to achieve similar things,
+  // nothing to be done here.
+  // if (ConstantFoldsToSimpleInteger(S.getCond(), ConstantCondValue))...
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andykaylor wrote:

As long as the implementation is missing in the upstream repo, a MissingFeatures assert is appropriate.

https://github.com/llvm/llvm-project/pull/137106