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Date:      Tue, 29 Oct 2019 16:51:12 +0000 (UTC)
From:      Dimitry Andric <dim@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r354146 - head/contrib/llvm/lib/TableGen
Message-ID:  <201910291651.x9TGpC2b089282@repo.freebsd.org>
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Author: dim
Date: Tue Oct 29 16:51:12 2019
New Revision: 354146
URL: https://svnweb.freebsd.org/changeset/base/354146

Log:
  Pull in r373338 from upstream llvm trunk (by Simon Pilgrim):
  
    Revert rL349624 : Let TableGen write output only if it changed,
    instead of doing so in cmake, attempt 2
  
    Differential Revision: https://reviews.llvm.org/D55842
    -----------------
    As discussed on PR43385 this is causing Visual Studio msbuilds to
    perpetually rebuild all tablegen generated files
  
  Pull in r373664 from upstream llvm trunk (by Nico Weber):
  
    Reland r349624: Let TableGen write output only if it changed, instead
    of doing so in cmake
  
    Move the write-if-changed logic behind a flag and don't pass it with
    the MSVC generator. msbuild doesn't have a restat optimization, so
    not doing write-if-change there doesn't have a cost, and it should
    fix whatever causes PR43385.
  
  This should fix the scenario where an incremental build from before
  r353358 (the clang 9.0.0 upgrade) to r353358 or later fails to update
  the timestamp of the generated lib/clang/headers/arm_fp16.h header.
  
  After such a build, installing world from read-only source and object
  directories would attempt to generate the header again, leading to
  "clang-tblgen: error opening arm_fp16.h.d:Read-only file system".
  
  Reported by:	avg, np
  PR:		241402
  MFC after:	1 month
  X-MFC-With:	r353358

Modified:
  head/contrib/llvm/lib/TableGen/Main.cpp

Modified: head/contrib/llvm/lib/TableGen/Main.cpp
==============================================================================
--- head/contrib/llvm/lib/TableGen/Main.cpp	Tue Oct 29 09:47:12 2019	(r354145)
+++ head/contrib/llvm/lib/TableGen/Main.cpp	Tue Oct 29 16:51:12 2019	(r354146)
@@ -49,6 +49,9 @@ static cl::list<std::string>
 MacroNames("D", cl::desc("Name of the macro to be defined"),
             cl::value_desc("macro name"), cl::Prefix);
 
+static cl::opt<bool>
+WriteIfChanged("write-if-changed", cl::desc("Only write output if it changed"));
+
 static int reportError(const char *ProgName, Twine Msg) {
   errs() << ProgName << ": " << Msg;
   errs().flush();
@@ -114,12 +117,14 @@ int llvm::TableGenMain(char *argv0, TableGenMainFn *Ma
       return Ret;
   }
 
-  // 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;
+  if (WriteIfChanged) {
+    // 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 OutFile(OutputFilename, EC, sys::fs::F_Text);

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