Add ability to turn off -fpch-instantiate-templates in clang-cl

A lot of our code building with clang-cl.exe using Clang 11 was failing with
the following 2 type of errors:

1. explicit specialization of 'foo' after instantiation
2. no matching function for call to 'bar'

Note that we also use -fdelayed-template-parsing in our builds.

I tried pretty hard to get a small repro for these failures, but couldn't. So
there is some subtle edge case in the -fpch-instantiate-templates feature
introduced by this change: https://reviews.llvm.org/D69585

When I tried turning this off using -fno-pch-instantiate-templates, builds
would silently fail with the same error without any indication that
-fno-pch-instantiate-templates was being ignored by the compiler. Then I
realized this "no" option wasn't actually working when I ran Clang under a
debugger.

Differential revision: https://reviews.llvm.org/D88680

Author: shivanshu3

clang/include/clang/Driver/Options.td

@@ -1479,11 +1479,11 @@ def fno_pch_validate_input_files_content:
   Group<f_Group>, Flags<[DriverOption]>;
 def fpch_instantiate_templates:
   Flag <["-"], "fpch-instantiate-templates">,
-  Group<f_Group>, Flags<[CC1Option]>,
+  Group<f_Group>, Flags<[CC1Option, CoreOption]>,
   HelpText<"Instantiate templates already while building a PCH">;
 def fno_pch_instantiate_templates:
   Flag <["-"], "fno-pch-instantiate-templates">,
-  Group<f_Group>, Flags<[CC1Option]>;
+  Group<f_Group>, Flags<[CC1Option, CoreOption]>;
 defm pch_codegen: OptInFFlag<"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: OptInFFlag<"pch-debuginfo", "Generate ", "Do not generate ",

clang/lib/Driver/ToolChains/Clang.cpp

@@ -1212,7 +1212,11 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
     if (YcArg && JA.getKind() >= Action::PrecompileJobClass &&
         JA.getKind() <= Action::AssembleJobClass) {
       CmdArgs.push_back(Args.MakeArgString("-building-pch-with-obj"));
-      CmdArgs.push_back(Args.MakeArgString("-fpch-instantiate-templates"));
+      // -fpch-instantiate-templates is the default when creating
+      // precomp using /Yc
+      if (Args.hasFlag(options::OPT_fpch_instantiate_templates,
+                       options::OPT_fno_pch_instantiate_templates, true))
+        CmdArgs.push_back(Args.MakeArgString("-fpch-instantiate-templates"));
     }
     if (YcArg || YuArg) {
       StringRef ThroughHeader = YcArg ? YcArg->getValue() : YuArg->getValue();

clang/test/Driver/pch-instantiate-templates.c

@@ -0,0 +1,13 @@
+// CL driver test cases
+// RUN: %clang_cl -### /Yc /Fpfoo.pch /Fofoo.obj -- %s 2>&1 | FileCheck --check-prefix=CLANG_CL_YC %s
+// RUN: %clang_cl -### /Yc /Fpfoo.pch /Fofoo.obj -fno-pch-instantiate-templates -- %s 2>&1 | FileCheck --check-prefix=CLANG_CL_YC_DISABLE %s
+
+// CLANG_CL_YC: "-fpch-instantiate-templates"
+// CLANG_CL_YC_DISABLE-NOT: "-fpch-instantiate-templates"
+
+// GCC driver test cases
+// RUN: %clang -### -x c-header %s -o %t/foo.pch 2>&1 | FileCheck -check-prefix=GCC_DEFAULT %s
+// RUN: %clang -### -x c-header %s -o %t/foo.pch -fpch-instantiate-templates 2>&1 | FileCheck -check-prefix=GCC_DEFAULT_ENABLE %s
+
+// GCC_DEFAULT-NOT: "-fpch-instantiate-templates"
+// GCC_DEFAULT_ENABLE: "-fpch-instantiate-templates"