[llvm] r330742 - Let TableGen write output only if it changed, instead of doing so in cmake.

[Nico Weber via llvm-commits]

Author: nico
Date: Tue Apr 24 10:29:05 2018
New Revision: 330742

URL: http://llvm.org/viewvc/llvm-project?rev=330742&view=rev
Log:
Let TableGen write output only if it changed, instead of doing so in cmake.

Removes one subprocess and one temp file from the build for each tablegen
invocation.

No intended behavior change.

https://reviews.llvm.org/D45899

Modified:
    llvm/trunk/cmake/modules/TableGen.cmake
    llvm/trunk/lib/TableGen/Main.cpp

Modified: llvm/trunk/cmake/modules/TableGen.cmake
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/cmake/modules/TableGen.cmake?rev=330742&r1=330741&r2=330742&view=diff
==============================================================================
--- llvm/trunk/cmake/modules/TableGen.cmake (original)
+++ llvm/trunk/cmake/modules/TableGen.cmake Tue Apr 24 10:29:05 2018
@@ -25,7 +25,7 @@ function(tablegen project ofn)
     file(RELATIVE_PATH ofn_rel
       ${CMAKE_BINARY_DIR} ${CMAKE_CURRENT_BINARY_DIR}/${ofn})
     set(additional_cmdline
-      -o ${ofn_rel}.tmp
+      -o ${ofn_rel}
       -d ${ofn_rel}.d
       WORKING_DIRECTORY ${CMAKE_BINARY_DIR}
       DEPFILE ${CMAKE_CURRENT_BINARY_DIR}/${ofn}.d
@@ -36,7 +36,7 @@ function(tablegen project ofn)
     file(GLOB local_tds "*.td")
     file(GLOB_RECURSE global_tds "${LLVM_MAIN_INCLUDE_DIR}/llvm/*.td")
     set(additional_cmdline
-      -o ${CMAKE_CURRENT_BINARY_DIR}/${ofn}.tmp
+      -o ${CMAKE_CURRENT_BINARY_DIR}/${ofn}
       )
   endif()
 
@@ -69,8 +69,7 @@ function(tablegen project ofn)
   # dependency twice in the result file when
   # ("${${project}_TABLEGEN_TARGET}" STREQUAL "${${project}_TABLEGEN_EXE}")
   # but lets us having smaller and cleaner code here.
-  add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${ofn}.tmp
-    # Generate tablegen output in a temporary file.
+  add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${ofn}
     COMMAND ${${project}_TABLEGEN_EXE} ${ARGN} -I ${CMAKE_CURRENT_SOURCE_DIR}
     ${LLVM_TABLEGEN_FLAGS}
     ${LLVM_TARGET_DEFINITIONS_ABSOLUTE}
@@ -83,20 +82,9 @@ function(tablegen project ofn)
     ${LLVM_TARGET_DEFINITIONS_ABSOLUTE}
     COMMENT "Building ${ofn}..."
     )
-  add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${ofn}
-    # Only update the real output file if there are any differences.
-    # This prevents recompilation of all the files depending on it if there
-    # aren't any.
-    COMMAND ${CMAKE_COMMAND} -E copy_if_different
-        ${CMAKE_CURRENT_BINARY_DIR}/${ofn}.tmp
-        ${CMAKE_CURRENT_BINARY_DIR}/${ofn}
-    DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/${ofn}.tmp
-    COMMENT "Updating ${ofn}..."
-    )
 
   # `make clean' must remove all those generated files:
-  set_property(DIRECTORY APPEND
-    PROPERTY ADDITIONAL_MAKE_CLEAN_FILES ${ofn}.tmp ${ofn})
+  set_property(DIRECTORY APPEND PROPERTY ADDITIONAL_MAKE_CLEAN_FILES ${ofn})
 
   set(TABLEGEN_OUTPUT ${TABLEGEN_OUTPUT} ${CMAKE_CURRENT_BINARY_DIR}/${ofn} PARENT_SCOPE)
   set_source_files_properties(${CMAKE_CURRENT_BINARY_DIR}/${ofn} PROPERTIES

Modified: llvm/trunk/lib/TableGen/Main.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/TableGen/Main.cpp?rev=330742&r1=330741&r2=330742&view=diff
==============================================================================
--- llvm/trunk/lib/TableGen/Main.cpp (original)
+++ llvm/trunk/lib/TableGen/Main.cpp Tue Apr 24 10:29:05 2018
@@ -96,8 +96,21 @@ int llvm::TableGenMain(char *argv0, Tabl
   if (Parser.ParseFile())
     return 1;
 
+  // Write output to memory.
+  std::string OutString;
+  raw_string_ostream Out(OutString);
+  if (MainFn(Out, Records))
+    return 1;
+
+  // Only updates the real output file if there are any differences.
+  // This prevents recompilation of all the files depending on it if there
+  // aren't any.
+  if (auto ExistingOrErr = MemoryBuffer::getFile(OutputFilename))
+    if (std::move(ExistingOrErr.get())->getBuffer() == Out.str())
+      return 0;
+
   std::error_code EC;
-  ToolOutputFile Out(OutputFilename, EC, sys::fs::F_Text);
+  ToolOutputFile OutFile(OutputFilename, EC, sys::fs::F_Text);
   if (EC)
     return reportError(argv0, "error opening " + OutputFilename + ":" +
                                   EC.message() + "\n");
@@ -105,14 +118,12 @@ int llvm::TableGenMain(char *argv0, Tabl
     if (int Ret = createDependencyFile(Parser, argv0))
       return Ret;
   }
-
-  if (MainFn(Out.os(), Records))
-    return 1;
+  OutFile.os() << Out.str();
 
   if (ErrorsPrinted > 0)
     return reportError(argv0, Twine(ErrorsPrinted) + " errors.\n");
 
   // Declare success.
-  Out.keep();
+  OutFile.keep();
   return 0;
 }