Reland: "[Frontend][PCH]-Add support for ignoring PCH options (-ignore-pch). (#142409)" (#143614)

Visual Studio has an argument to ignore all PCH related switches. clang-cl has also support option /Y-. Having the same option in clang would be helpful. This commit is to add support for ignoring PCH options (-ignore-pch). The commit includes: 1. Implement -ignore-pch as a Driver option. 2. Add a Driver test and a PCH test. 3. Add a section of -ignore-pch to user manual. 4. Add a release note for the new option '-ignore-pch'. The change since the original landing: 1. preprocessing-only mode doesn't imply that -include-pch is disabled. Co-authored-by: Matheus Izvekov <mizvekov@gmail.com>
2025-06-17 10:54:22 +01:00
parent 4c8f434409
commit 6f29837659
8 changed files with 167 additions and 2 deletions
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -339,6 +339,8 @@ New Compiler Flags

 - New option ``-Wnrvo`` added and disabled by default to warn about missed NRVO opportunities.

+- New option ``-ignore-pch`` added to disable precompiled headers. It overrides ``-emit-pch`` and ``-include-pch``. (#GH142409, `PCHDocs <https://clang.llvm.org/docs/UsersManual.html#ignoring-a-pch-file>`_).
+
 Deprecated Compiler Flags
 -------------------------

--- a/clang/docs/UsersManual.rst
+++ b/clang/docs/UsersManual.rst
@@ -1458,6 +1458,19 @@ will be processed from the PCH file. Otherwise, Clang will report an error.
  ``test.h`` since ``test.h`` was included directly in the source file and not
  specified on the command line using ``-include-pch``.

+Ignoring a PCH File
+^^^^^^^^^^^^^^^^^^^
+
+To ignore PCH options, a `-ignore-pch` option is passed to ``clang``:
+
+.. code-block:: console
+
+  $ clang -x c-header test.h -Xclang -ignore-pch -o test.h.pch
+  $ clang -include-pch test.h.pch -Xclang -ignore-pch test.c -o test
+
+This option disables precompiled headers, overrides -emit-pch and -include-pch.
+test.h.pch is not generated and not used as a prefix header.
+
 Relocatable PCH Files
 ^^^^^^^^^^^^^^^^^^^^^

--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3351,6 +3351,9 @@ defm pch_codegen: OptInCC1FFlag<"pch-codegen", "Generate ", "Do not generate ",
  "code for uses of this PCH that assumes an explicit object file will be built for the PCH">;
 defm pch_debuginfo: OptInCC1FFlag<"pch-debuginfo", "Generate ", "Do not generate ",
  "debug info for types in an object file built from this PCH and do not generate them elsewhere">;
+def ignore_pch : Flag<["-"], "ignore-pch">, Group<f_Group>,
+  Visibility<[ClangOption]>,
+  HelpText<"Disable precompiled headers, overrides -emit-pch and -include-pch">;

 def fimplicit_module_maps : Flag <["-"], "fimplicit-module-maps">, Group<f_Group>,
  Visibility<[ClangOption, CC1Option, CLOption]>,
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -4331,6 +4331,14 @@ void Driver::handleArguments(Compilation &C, DerivedArgList &Args,
    YcArg = YuArg = nullptr;
  }

+  if (Args.hasArg(options::OPT_include_pch) &&
+      Args.hasArg(options::OPT_ignore_pch)) {
+    // If -ignore-pch is used, -include-pch is disabled. Since -emit-pch is
+    // CC1option, it will not be added to command argments if -ignore-pch is
+    // used.
+    Args.eraseArg(options::OPT_include_pch);
+  }
+
  bool LinkOnly = phases::Link == FinalPhase && Inputs.size() > 0;
  for (auto &I : Inputs) {
    types::ID InputType = I.first;
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -5202,7 +5202,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
      CmdArgs.push_back("-emit-module-interface");
    else if (JA.getType() == types::TY_HeaderUnit)
      CmdArgs.push_back("-emit-header-unit");
-    else
+    else if (!Args.hasArg(options::OPT_ignore_pch))
      CmdArgs.push_back("-emit-pch");
  } else if (isa<VerifyPCHJobAction>(JA)) {
    CmdArgs.push_back("-verify-pch");
@@ -5259,6 +5259,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
    } else if (JA.getType() == types::TY_PP_Asm) {
      CmdArgs.push_back("-S");
    } else if (JA.getType() == types::TY_AST) {
+      if (!Args.hasArg(options::OPT_ignore_pch))
        CmdArgs.push_back("-emit-pch");
    } else if (JA.getType() == types::TY_ModuleFile) {
      CmdArgs.push_back("-module-file-info");
--- a/clang/test/Driver/ignored-pch.cpp
+++ b/clang/test/Driver/ignored-pch.cpp
@@ -0,0 +1,19 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+
+// Create PCH without -ignore-pch.
+// RUN: %clang -x c++-header %S/Inputs/pchfile.h -### 2>&1 | FileCheck %s -check-prefix=CHECK-EMIT-PCH
+// RUN: %clang -x c++-header %S/Inputs/pchfile.h -o %t/pchfile.h.pch
+// RUN: %clang %s -include-pch %t/pchfile.h.pch -### 2>&1 | FileCheck %s -check-prefix=CHECK-INCLUDE-PCH
+// RUN: %clang %s -emit-ast -include-pch %t/pchfile.h.pch -### 2>&1 | FileCheck %s -check-prefixes=CHECK-EMIT-PCH,CHECK-INCLUDE-PCH
+
+
+// Create PCH with -ignore-pch.
+// RUN: %clang -x c++-header -ignore-pch %S/Inputs/pchfile.h -### 2>&1 | FileCheck %s -check-prefix=CHECK-IGNORE-PCH
+// RUN: %clang %s -ignore-pch -include-pch  %t/pchfile.h.pch -### 2>&1 | FileCheck %s -check-prefix=CHECK-IGNORE-PCH
+// RUN: %clang %s -ignore-pch -emit-ast -include-pch %t/pchfile.h.pch -### 2>&1 | FileCheck %s -check-prefix=CHECK-IGNORE-PCH
+
+// CHECK-EMIT-PCH: -emit-pch
+// CHECK-INCLUDE-PCH: -include-pch
+// CHECK-IGNORE-PCH-NOT: -emit-pch
+// CHECK-IGNORE-PCH-NOT: -include-pch
--- a/clang/test/PCH/Inputs/ignored-pch.h
+++ b/clang/test/PCH/Inputs/ignored-pch.h
@@ -0,0 +1,6 @@
+#ifndef IGNORED_PCH_H
+#define IGNORED_PCH_H
+inline int f() {
+  return 42;
+}
+#endif // IGNORED_PCH_H
--- a/clang/test/PCH/ignored-pch.c
+++ b/clang/test/PCH/ignored-pch.c
@@ -0,0 +1,113 @@
+// RUN: rm -rf %t.pch %t.ll
+// RUN: %clang -x c-header %S/Inputs/ignored-pch.h -o %t.pch
+// RUN: %clang -S -emit-llvm %s -include-pch %t.pch -o %t.ll
+// RUN: ls %t.pch | FileCheck --check-prefix=CHECK-PCH %s
+// RUN: ls %t.ll | FileCheck --check-prefix=CHECK-OBJ %s
+
+// RUN: rm -rf %t.pch %t.ll
+// RUN: %clang -x c-header %S/Inputs/ignored-pch.h -o %t.pch
+// RUN: %clang %s -emit-ast -include-pch %t.pch -o %t.ll
+// RUN: ls %t.pch | FileCheck --check-prefix=CHECK-PCH %s
+// RUN: ls %t.ll | FileCheck --check-prefix=CHECK-OBJ %s
+
+// Check that -ignore-pch causes -emit-pch and -include-pch options to be ignored.
+// RUN: rm -rf %t.pch %t.ll
+// RUN: %clang -x c-header %S/Inputs/ignored-pch.h -ignore-pch -o %t.pch
+// RUN: %clang -S -emit-llvm %s -include-pch %t.pch -ignore-pch -o %t.ll
+// RUN: not ls %t.pch 2>&1 | FileCheck --check-prefix=CHECK-PCH-ERROR %s
+// RUN: ls %t.ll 2>&1 | FileCheck --check-prefix=CHECK-OBJ %s
+
+// RUN: rm -rf %t.pch %t.ll
+// RUN: %clang -emit-ast %s -include-pch %t.pch -ignore-pch -o %t.ll
+// RUN: not ls %t.ll 2>&1 | FileCheck --check-prefix=CHECK-OBJ-ERROR %s
+
+// Check that -ignore-pch works for multiple PCH related options.
+// Test with -building-pch-with-obj.
+// RUN: rm -rf %t.pch %t.ll
+// RUN: %clang -x c-header %S/Inputs/ignored-pch.h -ignore-pch -Xclang -building-pch-with-obj -o %t.pch
+// RUN: %clang -S -emit-llvm %s -include-pch %t.pch -ignore-pch -Xclang -building-pch-with-obj -o %t.ll
+// RUN: not ls %t.pch 2>&1 | FileCheck --check-prefix=CHECK-PCH-ERROR %s
+// RUN: ls %t.ll | FileCheck --check-prefix=CHECK-OBJ %s
+
+// Test with -fallow-pch-with-compiler-errors.
+// RUN: rm -rf %t.pch %t.ll
+// RUN: %clang -x c-header %S/Inputs/ignored-pch.h -ignore-pch -Xclang -fallow-pch-with-compiler-errors -o %t.pch
+// RUN: %clang -S -emit-llvm %s -include-pch %t.pch -ignore-pch -Xclang -fallow-pch-with-compiler-errors -o %t.ll
+// RUN: not ls %t.pch 2>&1 | FileCheck --check-prefix=CHECK-PCH-ERROR %s
+// RUN: ls %t.ll | FileCheck --check-prefix=CHECK-OBJ %s
+
+// Test with -fallow-pch-with-different-modules-cache-path.
+// RUN: rm -rf %t.pch %t.ll
+// RUN: %clang -x c-header %S/Inputs/ignored-pch.h -ignore-pch -Xclang -fallow-pch-with-different-modules-cache-path -o %t.pch
+// RUN: %clang -S -emit-llvm %s -ignore-pch -include-pch %t.pch -Xclang -fallow-pch-with-different-modules-cache-path -o %t.ll
+// RUN: not ls %t.pch 2>&1 | FileCheck --check-prefix=CHECK-PCH-ERROR %s
+// RUN: ls %t.ll | FileCheck --check-prefix=CHECK-OBJ %s
+
+// Test with -fpch-codegen.
+// RUN: rm -rf %t.pch %t.ll
+// RUN: %clang -x c-header %S/Inputs/ignored-pch.h -ignore-pch -fpch-codegen -o %t.pch
+// RUN: %clang -S -emit-llvm %s -include-pch %t.pch -ignore-pch -fpch-codegen -o %t.ll
+// RUN: not ls %t.pch 2>&1 | FileCheck --check-prefix=CHECK-PCH-ERROR %s
+// RUN: ls %t.ll | FileCheck --check-prefix=CHECK-OBJ %s
+
+// Test with -fpch-debuginfo.
+// RUN: rm -rf %t.pch %t.ll
+// RUN: %clang -x c-header %S/Inputs/ignored-pch.h -ignore-pch -fpch-debuginfo -o %t.pch
+// RUN: %clang -S -emit-llvm %s -include-pch %t.pch -ignore-pch -fpch-debuginfo -o %t.ll
+// RUN: not ls %t.pch 2>&1 | FileCheck --check-prefix=CHECK-PCH %s
+// RUN: ls %t.ll | FileCheck --check-prefix=CHECK-OBJ %s
+
+// Test with -fpch-instantiate-templates.
+// RUN: rm -rf %t.pch %t.ll
+// RUN: %clang -x c-header %S/Inputs/ignored-pch.h -ignore-pch -fpch-instantiate-templates -o %t.pch
+// RUN: %clang -S -emit-llvm %s -include-pch %t.pch -ignore-pch -fpch-instantiate-templates -o %t.ll
+// RUN: not ls %t.pch 2>&1 | FileCheck --check-prefix=CHECK-PCH %s
+// RUN: ls %t.ll | FileCheck --check-prefix=CHECK-OBJ %s
+
+// Test with -fno-pch-timestamp.
+// RUN: rm -rf %t.pch %t.ll
+// RUN: %clang -x c-header %S/Inputs/ignored-pch.h -ignore-pch -Xclang -fno-pch-timestamp -o %t.pch
+// RUN: %clang -S -emit-llvm %s -include-pch %t.pch -ignore-pch -Xclang -fno-pch-timestamp -o %t.ll
+// RUN: not ls %t.pch 2>&1 | FileCheck --check-prefix=CHECK-PCH %s
+// RUN: ls %t.ll | FileCheck --check-prefix=CHECK-OBJ %s
+
+// Test with -fno-validate-pch.
+// RUN: rm -rf %t.pch %t.ll
+// RUN: %clang -x c-header %S/Inputs/ignored-pch.h -ignore-pch -Xclang -fno-validate-pch -o %t.pch
+// RUN: %clang -S -emit-llvm %s -include-pch %t.pch -ignore-pch -Xclang -fno-validate-pch -o %t.ll
+// RUN: not ls %t.pch 2>&1 | FileCheck --check-prefix=CHECK-PCH %s
+// RUN: ls %t.ll | FileCheck --check-prefix=CHECK-OBJ %s
+
+// Test with -relocatable-pch.
+// RUN: rm -rf %t.pch %t.ll
+// RUN: %clang -x c-header %S/Inputs/ignored-pch.h -ignore-pch -relocatable-pch -o %t.pch
+// RUN: %clang -S -emit-llvm %s -include-pch %t.pch -ignore-pch -relocatable-pch -o %t.ll
+// RUN: not ls %t.pch 2>&1 | FileCheck --check-prefix=CHECK-PCH %s
+// RUN: ls %t.ll | FileCheck --check-prefix=CHECK-OBJ %s
+
+// Test with -pch-through-hdrstop-create/-pch-through-hdrstop-use
+// RUN: rm -rf %t.pch %t.ll
+// RUN: %clang -x c-header %S/Inputs/ignored-pch.h -ignore-pch -Xclang -pch-through-hdrstop-create -o %t.pch
+// RUN: %clang -S -emit-llvm %s -include-pch %t.pch -ignore-pch -Xclang -pch-through-hdrstop-use -o %t.ll
+// RUN: not ls %t.pch 2>&1 | FileCheck --check-prefix=CHECK-PCH %s
+// RUN: ls %t.ll | FileCheck --check-prefix=CHECK-OBJ %s
+
+
+// Test with AST dump output:
+// RUN: rm -rf %t.pch %t.ll
+// RUN: %clang -x c-header %S/Inputs/ignored-pch.h -o %t.pch
+// RUN: %clang %s -include-pch %t.pch -Xclang -ast-dump-all -c | FileCheck --check-prefix=CHECK-AST-PCH %s
+// RUN: %clang %s -include-pch %t.pch -ignore-pch -Xclang -ast-dump-all -c | FileCheck --check-prefix=CHECK-AST %s
+
+// CHECK-PCH: ignored-pch.c.{{.*}}.pch
+// CHECK-OBJ: ignored-pch.c.{{.*}}.ll
+// CHECK-PCH-ERROR: ignored-pch.c.{{.*}}.pch{{'?}}: No such file or directory
+// CHECK-OBJ-ERROR: ignored-pch.c.{{.*}}.ll{{'?}}: No such file or directory
+// CHECK-AST-PCH: <undeserialized declarations>
+// CHECK-AST-NOT: <undeserialized declarations>
+
+#pragma hdrstop
+#include "Inputs/ignored-pch.h"
+int main() {
+  return f();
+}