Allow suppressing host and target info in VersionPrinter

[pammon]

Summary

VersionPrinter by default outputs information about the Host CPU
and Default target. Printing this information requires linking in
a large amount of data, such as supported target triples as C
strings, which in turn bloats the binary size.

Enable a new CMake option LLVM_VERSION_PRINTER_SHOW_HOST_TARGET_INFO
which controls printing of the host and target info. This allows
the target triple names to be dead-code stripped. This is a nice
win for LLVM clients that wish to minimize their binary size, such
as graphics drivers.

By default this is ON, so there is no change in the default behavior.
Clients who wish to suppress this printing can do so by setting this
option to off via CMake.

A test app on Linux that uses ParseCommandLineOptions() shows a binary
size reduction of 23KB (from 149K to 126K) for a Release build, and 24KB
(from 135K to 111K) in a MinSizeRel build.

[chandlerc]

This seems like a totally nice direction, but I wonder if I could convince you to scope creep this a bit?

I feel like this shouldn't be guarded by a macro at all. Instead, for tools where it makes sense, we should have an API they can call (perhaps instead of or in addition to this) which provides this level of information in their version strings.

For example, I don't ever want clang-format or FileCheck to care about this. But I'd rather like opt, llc, and clang to always show it. And for those, it costs them nothing as this code is going to get linked in anyways.

What do you think?

[compnerd]

I think that the idea that you propose is good, however, I think that may be better to do as a follow up. This would get the immediate benefit for the tooling, and we can work out a nicer way to expose the information to the other users. Making it something which each app does means that we would need to change all the apps as well, which would be a much larger change.

[chandlerc]

In D30904#706747, @compnerd wrote:

I think that the idea that you propose is good, however, I think that may be better to do as a follow up. This would get the immediate benefit for the tooling, and we can work out a nicer way to expose the information to the other users. Making it something which each app does means that we would need to change all the apps as well, which would be a much larger change.

OK, but if you want to go the current route, it needs more work too.

First, there is no corresponding CMake change to allow us to set the macro.

But once you do that, we'll get to the core issue I think I have here. I don't think we want to lose this information from tools like opt, llc, and clang where it is *very* useful. So that'll cause the default for this CMake variable to be set in the direction that doesn't get us any benefit by default. If that's enough for you, then OK. But if you want this to be available for tooling *by default* I think we need to at least do the initial work of making this controllable to avoid regressing the debug information provided in Clang and other binary's version string.

[pammon]

Are the changes in config.h.cmake not sufficient to enable setting this variable? I was able to set the variable in my tests by invoke cmake with -DLLVM_VERSION_PRINTER_NO_HOST_TARGET_INFO=1.

I'm not proposing this be set by default. This is something that clients would need to opt into, via the cmake option above.

[compnerd]

I think that @chandlerc is suggesting making it a CMake option (see the option function in CMake) to provide documentation for this for users. I think that is a pretty reasonable ask, as it aids in discoverability of this.

[pammon]

Use CMake's option() to improve discoverability. Invert sense of option to improve clarity.

[pammon]

@chandlerc will you please take a look at my most recent changes? Thank you

[pammon]

ping @chandlerc

[compnerd]

This is opt-out by default, so it shouldn't have any impact on users by default. When building for tooling, this should allow smaller builds for those.

[trentxintong]

Committed for coworker.

CMakeLists.txt

 set(LLVM_INSTALL_DOXYGEN_HTML_DIR "share/doc/llvm/doxygen-html"
     CACHE STRING "Doxygen-generated HTML documentation install directory")
 set(LLVM_INSTALL_OCAMLDOC_HTML_DIR "share/doc/llvm/ocaml-html"
     CACHE STRING "OCamldoc-generated HTML documentation install directory")
 
 option (LLVM_BUILD_EXTERNAL_COMPILER_RT
   "Build compiler-rt as an external project." OFF)
 
+option (LLVM_VERSION_PRINTER_SHOW_HOST_TARGET_INFO
+  "Show target and host info when tools are invoked with --version." ON)
+
 # You can configure which libraries from LLVM you want to include in the
 # shared library by setting LLVM_DYLIB_COMPONENTS to a semi-colon delimited
 # list of LLVM components. All component names handled by llvm-config are valid.
 if(NOT DEFINED LLVM_DYLIB_COMPONENTS)
   set(LLVM_DYLIB_COMPONENTS "all" CACHE STRING
     "Semicolon-separated list of components to include in libLLVM, or \"all\".")
 endif()
 option(LLVM_LINK_LLVM_DYLIB "Link tools against the libllvm dynamic library" OFF)

include/llvm/Config/config.h.cmake

 #cmakedefine01 LLVM_USE_INTEL_JITEVENTS
 
 /* Define if we have the oprofile JIT-support library */
 #cmakedefine01 LLVM_USE_OPROFILE
 
 /* LLVM version information */
 #cmakedefine LLVM_VERSION_INFO "${LLVM_VERSION_INFO}"
 
+/* Whether tools show host and target info when invoked with --version */
+#cmakedefine01 LLVM_VERSION_PRINTER_SHOW_HOST_TARGET_INFO
+
 /* Major version of the LLVM API */
 #define LLVM_VERSION_MAJOR ${LLVM_VERSION_MAJOR}
 
 /* Minor version of the LLVM API */
 #define LLVM_VERSION_MINOR ${LLVM_VERSION_MINOR}
 
 /* Patch version of the LLVM API */
 #define LLVM_VERSION_PATCH ${LLVM_VERSION_PATCH}

lib/Support/CommandLine.cpp

 #ifndef __OPTIMIZE__
     OS << "DEBUG build";
 #else
     OS << "Optimized build";
 #endif
 #ifndef NDEBUG
     OS << " with assertions";
 #endif
+#if LLVM_VERSION_PRINTER_SHOW_HOST_TARGET_INFO
     std::string CPU = sys::getHostCPUName();
     if (CPU == "generic")
       CPU = "(unknown)";
     OS << ".\n"
        << "  Default target: " << sys::getDefaultTargetTriple() << '\n'
-       << "  Host CPU: " << CPU << '\n';
+       << "  Host CPU: " << CPU;
+#endif
+    OS << '\n';
   }
   void operator=(bool OptionWasSpecified) {
     if (!OptionWasSpecified)
       return;
 
     if (OverrideVersionPrinter != nullptr) {
       (*OverrideVersionPrinter)();
       exit(0);