[Frontend][PCH]-Add support for ignoring PCH options (-ignore-pch).

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
 -------------------------
 

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
 ^^^^^^^^^^^^^^^^^^^^^
 

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]>,

clang/lib/Driver/Driver.cpp

@@ -4331,6 +4331,15 @@ void Driver::handleArguments(Compilation &C, DerivedArgList &Args,
     YcArg = YuArg = nullptr;
   }
 
+  if (Args.hasArg(options::OPT_include_pch) &&
+      (FinalPhase == phases::Preprocess ||
+       Args.hasArg(options::OPT_ignore_pch))) {
+    // If only preprocessing or -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;

clang/lib/Driver/ToolChains/Clang.cpp

@@ -5321,7 +5321,7 @@ 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");
@@ -5378,7 +5378,8 @@ 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) {

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

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

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();
+}