https://github.com/MaskRay created
https://github.com/llvm/llvm-project/pull/231068
clangCIR reuses clangAST's precompiled header, so each of its 54 files
reparses the MLIR and CIR dialect headers. Add a private PCH like
clangCodeGen's (#206018).
Rebuilding clangCIR (Release+Asserts, 28 threads):
```
summed per-file user CPU wall
before 312 s 282 s 20.0 s
after 79 s + 6 s PCH 78 s 18.1 s
```
LLM-aided
>From 671b929428cf7bac49eabe24f96eea8787b8a980 Mon Sep 17 00:00:00 2001
From: Fangrui Song <[email protected]>
Date: Sun, 11 Oct 2026 15:29:08 -0700
Subject: [PATCH] [CIR][CMake] Add PCH for clangCIR. NFC
clangCIR reuses clangAST's precompiled header, so each of its 54 files
reparses the MLIR and CIR dialect headers. Add a private PCH like
clangCodeGen's (#206018).
Rebuilding clangCIR (Release+Asserts, 28 threads):
```
summed per-file user CPU wall
before 312 s 282 s 20.0 s
after 79 s + 6 s PCH 78 s 18.1 s
```
LLM-aided
---
clang/lib/CIR/CodeGen/CMakeLists.txt | 4 ++++
clang/lib/CIR/CodeGen/pch.h | 23 +++++++++++++++++++++++
2 files changed, 27 insertions(+)
create mode 100644 clang/lib/CIR/CodeGen/pch.h
diff --git a/clang/lib/CIR/CodeGen/CMakeLists.txt
b/clang/lib/CIR/CodeGen/CMakeLists.txt
index 1b5c0b91b394e..6d84faf70d11d 100644
--- a/clang/lib/CIR/CodeGen/CMakeLists.txt
+++ b/clang/lib/CIR/CodeGen/CMakeLists.txt
@@ -61,6 +61,10 @@ add_clang_library(clangCIR
Targets/NVPTX.cpp
Targets/SPIRV.cpp
+ DISABLE_PCH_REUSE # PCH contains private headers
+ PRECOMPILE_HEADERS
+ [["pch.h"]]
+
DEPENDS
MLIRCIR
MLIRCIROpInterfacesIncGen
diff --git a/clang/lib/CIR/CodeGen/pch.h b/clang/lib/CIR/CodeGen/pch.h
new file mode 100644
index 0000000000000..ab52fad5468ff
--- /dev/null
+++ b/clang/lib/CIR/CodeGen/pch.h
@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// Precompiled header for clangCIR. Uses private headers.
+///
+//===----------------------------------------------------------------------===//
+
+#include "CIRGenBuilder.h"
+#include "CIRGenCXXABI.h"
+#include "CIRGenFunction.h"
+#include "CIRGenModule.h"
+#include "CIRGenValue.h"
+#include "clang/AST/pch.h"
+#include "clang/CIR/Dialect/IR/CIRDialect.h"
+#include "clang/CIR/MissingFeatures.h"
+#include "mlir/IR/pch.h"
+#include "llvm/IR/pch.h"
+#include "llvm/Support/pch.h"
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