llvmbot wrote:

<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-driver

Author: Ying Yi (MaggieYingYi)

<details>
<summary>Changes</summary>

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'.

---
Full diff: https://github.com/llvm/llvm-project/pull/143614.diff


8 Files Affected:

- (modified) clang/docs/ReleaseNotes.rst (+2) 
- (modified) clang/docs/UsersManual.rst (+13) 
- (modified) clang/include/clang/Driver/Options.td (+3) 
- (modified) clang/lib/Driver/Driver.cpp (+8) 
- (modified) clang/lib/Driver/ToolChains/Clang.cpp (+3-2) 
- (added) clang/test/Driver/ignored-pch.cpp (+19) 
- (added) clang/test/PCH/Inputs/ignored-pch.h (+6) 
- (added) clang/test/PCH/ignored-pch.c (+113) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index f36c82bff2ef8..86287b28f0bf8 100644
--- 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
 -------------------------
 
diff --git a/clang/docs/UsersManual.rst b/clang/docs/UsersManual.rst
index 62844f7e6a2fa..284a404026dfe 100644
--- 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
 ^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/clang/include/clang/Driver/Options.td 
b/clang/include/clang/Driver/Options.td
index 3582efd7721b0..66d3dc921816d 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3348,6 +3348,9 @@ 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]>,
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 80728daca03c9..21489c8b0cde9 100644
--- 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;
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp 
b/clang/lib/Driver/ToolChains/Clang.cpp
index a74fa81f3cf5b..2d676aa0b9c8e 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -5184,7 +5184,7 @@ 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");
@@ -5241,7 +5241,8 @@ 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) {
-      CmdArgs.push_back("-emit-pch");
+      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");
     } else if (JA.getType() == types::TY_RewrittenObjC) {
diff --git a/clang/test/Driver/ignored-pch.cpp 
b/clang/test/Driver/ignored-pch.cpp
new file mode 100644
index 0000000000000..b237fc3cba57d
--- /dev/null
+++ 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/../Modules/Inputs/codegen-flags/foo.h -### 
2>&1 | FileCheck %s -check-prefix=CHECK-EMIT-PCH
+// RUN: %clang -x c++-header %S/../Modules/Inputs/codegen-flags/foo.h -o 
%t/foo.h.pch
+// RUN: %clang %s -include-pch %t/foo.h.pch -### 2>&1 | FileCheck %s 
-check-prefix=CHECK-INCLUDE-PCH
+// RUN: %clang %s -emit-ast -include-pch %t/foo.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/../Modules/Inputs/codegen-flags/foo.h -### 2>&1 | FileCheck %s 
-check-prefix=CHECK-IGNORE-PCH
+// RUN: %clang %s -ignore-pch -include-pch  %t/foo.h.pch -### 2>&1 | FileCheck 
%s -check-prefix=CHECK-IGNORE-PCH
+// RUN: %clang %s -ignore-pch -emit-ast -include-pch %t/foo.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
diff --git a/clang/test/PCH/Inputs/ignored-pch.h 
b/clang/test/PCH/Inputs/ignored-pch.h
new file mode 100644
index 0000000000000..56047037c331f
--- /dev/null
+++ 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
diff --git a/clang/test/PCH/ignored-pch.c b/clang/test/PCH/ignored-pch.c
new file mode 100644
index 0000000000000..5b64582cba618
--- /dev/null
+++ 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();
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/143614
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