Merge pull request #1381 from goplus/xgopilot/claude/document-outll-process-1730340128

docs(CLAUDE.md): document out.ll update process after IR changes

CLAUDE.md

@@ -51,6 +51,56 @@ go test ./...
 
 **Important:** The `LLGO_ROOT` environment variable must be set to the repository root when running llgo commands during development.
 
+### Update out.ll files after modifying compiler IR generation
+
+**CRITICAL:** When you modify the compiler's IR generation logic (especially in `ssa/` or `cl/` packages), you MUST update all out.ll test files under the `cl/` directory.
+
+#### Understanding out.ll files
+
+The `out.ll` files under the `cl/` directory are comparison IR files that serve as reference outputs for the test suite:
+- They are generated by `llgen` from the corresponding `in.go` files in the same directory
+- They reflect the current compiler's LLVM IR representation of the Go source code
+- They are used by tests to verify that the compiler generates correct and consistent IR output
+
+#### Required steps after modifying IR generation logic
+
+1. **Reinstall the tools** to apply your compiler changes:
+   ```bash
+   go install -v ./chore/gentests
+   go install -v ./chore/llgen
+   ```
+
+2. **Regenerate out.ll files**:
+   
+   **For batch updates (recommended)** - Use `gentests` to regenerate all test files:
+   ```bash
+   gentests
+   ```
+   This will automatically regenerate all out.ll files in these directories:
+   - `cl/_testlibc`
+   - `cl/_testlibgo`
+   - `cl/_testrt`
+   - `cl/_testgo`
+   - `cl/_testpy`
+   - `cl/_testdata`
+   
+   **For individual test inspection** - Use `llgen` to regenerate specific test directories:
+   ```bash
+   llgen cl/_testgo/interface
+   llgen cl/_testrt/tpmethod
+   ```
+
+3. **Verify the changes** make sense by reviewing the diff in the out.ll files
+
+4. **Commit the updated out.ll files** along with your compiler changes
+
+#### Why this matters
+
+This process ensures that:
+- The test suite reflects the current compiler behavior
+- Changes to IR generation are properly documented and reviewed
+- Future regressions can be detected by comparing against the reference output
+
 ## Code Quality
 
 Before submitting any code updates, you must run the following formatting and validation commands: