clang-cl: Remove -isystem, add -imsvc.

r260990 exposed -isystem in clang-cl. -isystem adds a directory to the front of
the system include search path. The idea was to use this to point to a hermetic
msvc install, but as it turns out this doesn't work: -isystem then adds the
hermetic headers in front of clang's builtin headers, and clang's headers that
are supposed to wrap msvc headers (say, stdarg.h) aren't picked up at all
anymore.

So revert that, and instead expose -imsvc which works as if the passed
directory was part of %INCLUDE%: The header is treated as a system header, but
it is searched after clang's lib/Header headers.

Fixes half of PRPR26751.

llvm-svn: 266108

5 files changed, 14 insertions, 6 deletions

diff --git a/clang/include/clang/Driver/CLCompatOptions.td b/clang/include/clang/Driver/CLCompatOptions.td
index b2f12c94059..a91a3fbbd84 100644
--- a/clang/include/clang/Driver/CLCompatOptions.td
+++ b/clang/include/clang/Driver/CLCompatOptions.td
@@ -210,6 +210,9 @@ def _SLASH_GX : CLFlag<"GX">,
   HelpText<"Enable exception handling">;
 def _SLASH_GX_ : CLFlag<"GX-">,
   HelpText<"Enable exception handling">;
+def _SLASH_imsvc : CLJoinedOrSeparate<"imsvc">,
+  HelpText<"Add directory to system include search path, as if part of %INCLUDE%">,
+  MetaVarName<"<dir>">;
 def _SLASH_LD : CLFlag<"LD">, HelpText<"Create DLL">;
 def _SLASH_LDd : CLFlag<"LDd">, HelpText<"Create debug DLL">;
 def _SLASH_link : CLRemainingArgs<"link">,
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index dadb475f43e..20c2677254e 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -1254,7 +1254,7 @@ def iquote : JoinedOrSeparate<["-"], "iquote">, Group<clang_i_Group>, Flags<[CC1
 def isysroot : JoinedOrSeparate<["-"], "isysroot">, Group<clang_i_Group>, Flags<[CC1Option]>,
   HelpText<"Set the system root directory (usually /)">, MetaVarName<"<dir>">;
 def isystem : JoinedOrSeparate<["-"], "isystem">, Group<clang_i_Group>,
-  Flags<[CC1Option, CoreOption]>,
+  Flags<[CC1Option]>,
   HelpText<"Add directory to SYSTEM include search path">, MetaVarName<"<directory>">;
 def iwithprefixbefore : JoinedOrSeparate<["-"], "iwithprefixbefore">, Group<clang_i_Group>,
   HelpText<"Set directory to include search path with prefix">, MetaVarName<"<dir>">,
diff --git a/clang/lib/Driver/MSVCToolChain.cpp b/clang/lib/Driver/MSVCToolChain.cpp
index e0552903aee..7f84d1f9d94 100644
--- a/clang/lib/Driver/MSVCToolChain.cpp
+++ b/clang/lib/Driver/MSVCToolChain.cpp
@@ -527,6 +527,10 @@ void MSVCToolChain::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
                                   "include");
   }
 
+  // Add %INCLUDE%-like directories from the -imsvc flag.
+  for (const auto &Path : DriverArgs.getAllArgValues(options::OPT__SLASH_imsvc))
+    addSystemInclude(DriverArgs, CC1Args, Path);
+
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
diff --git a/clang/test/Driver/cl-options.c b/clang/test/Driver/cl-options.c
index c9e857332d7..4f82c5ade17 100644
--- a/clang/test/Driver/cl-options.c
+++ b/clang/test/Driver/cl-options.c
@@ -82,6 +82,12 @@
 // RUN: %clang_cl /I myincludedir -### -- %s 2>&1 | FileCheck -check-prefix=SLASH_I %s
 // SLASH_I: "-I" "myincludedir"
 
+// RUN: %clang_cl /imsvcmyincludedir -### -- %s 2>&1 | FileCheck -check-prefix=SLASH_imsvc %s
+// RUN: %clang_cl /imsvc myincludedir -### -- %s 2>&1 | FileCheck -check-prefix=SLASH_imsvc %s
+// Clang's resource header directory should be first:
+// SLASH_imsvc: "-internal-isystem" "{{[^"]*}}lib{{.}}clang{{[^"]*}}include"
+// SLASH_imsvc: "-internal-isystem" "myincludedir"
+
 // RUN: %clang_cl /J -### -- %s 2>&1 | FileCheck -check-prefix=J %s
 // J: -fno-signed-char
 
@@ -452,7 +458,6 @@
 // RUN:     -fno-ms-compatibility \
 // RUN:     -fms-extensions \
 // RUN:     -fno-ms-extensions \
-// RUN:     -isystem=some/path \
 // RUN:     -mllvm -disable-llvm-optzns \
 // RUN:     -Wunused-variable \
 // RUN:     -fmacro-backtrace-limit=0 \
diff --git a/clang/test/Driver/cl-pch-search.cpp b/clang/test/Driver/cl-pch-search.cpp
index fd503f1f801..118cf19efbd 100644
--- a/clang/test/Driver/cl-pch-search.cpp
+++ b/clang/test/Driver/cl-pch-search.cpp
@@ -4,7 +4,3 @@
 // REQUIRES: x86-registered-target
 // Check that pchfile.h next to to pchfile.cc is found correctly.
 // RUN: %clang_cl -Werror /Ycpchfile.h /FIpchfile.h /c /Fo%t.obj /Fp%t.pch -- %S/Inputs/pchfile.cpp 
-
-// Check that i_group flags other than -include aren't skipped (e.g. -isystem).
-#include "header0.h"
-// RUN: %clang_cl -Werror -isystem%S/Inputs /Yupchfile.h /FIpchfile.h /c /Fo%t.obj /Fp%t.pch -- %s