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Pull in r373338 from upstream llvm trunk (by Simon Pilgrim):

Browse Source 
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
This commit is contained in:
Dimitry Andric 2019-10-29 16:51:12 +00:00
parent 65d553b0f0
commit f1eeb689ab
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=354146
1 changed files with 11 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
contrib/llvm/lib/TableGen/Main.cpp
View File

@ -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 *MainFn) {
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);