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[COFF] don't replace import library if contents are unchanged 

Summary:
This detects when an import library is about to be overwritten with a
newly built one with the same contents, and keeps the old library
instead. The use case for this is to avoid needlessly rebuilding
targets that depend on the import library in build systems that rely
on timestamps to determine whether a target requires rebuilding.

This feature was requested in PR35917.

Reviewers: rnk, ruiu, zturner, pcc

Reviewed By: ruiu

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D42326

llvm-svn: 323164
This commit is contained in:
Bob Haarman 2018-01-23 00:36:42 +00:00
parent 48b32f4ced
commit 4ce341ffb6
2 changed files with 42 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

41
lld/COFF/Driver.cpp
View File

@ -539,10 +539,39 @@ static void createImportLibrary(bool AsLib) {
Exports.push_back(E2);
}
auto E = writeImportLibrary(getImportName(AsLib), getImplibPath(), Exports,
Config->Machine, false, Config->MinGW);
handleAllErrors(std::move(E),
[&](ErrorInfoBase &EIB) { error(EIB.message()); });
auto HandleError = [](Error &&E) {
handleAllErrors(std::move(E),
[](ErrorInfoBase &EIB) { error(EIB.message()); });
};
std::string LibName = getImportName(AsLib);
std::string Path = getImplibPath();
// If the import library already exists, replace it only if the contents
// have changed.
ErrorOr<std::unique_ptr<MemoryBuffer>> OldBuf = MemoryBuffer::getFile(Path);
if (!OldBuf) {
HandleError(writeImportLibrary(LibName, Path, Exports, Config->Machine,
false, Config->MinGW));
return;
}
SmallString<128> TmpName;
if (std::error_code EC =
sys::fs::createUniqueFile(Path + ".tmp-%%%%%%%%.lib", TmpName))
fatal("cannot create temporary file for import library " + Path + ": " +
EC.message());
if (Error E = writeImportLibrary(LibName, TmpName, Exports, Config->Machine,
false, Config->MinGW)) {
HandleError(std::move(E));
return;
}
std::unique_ptr<MemoryBuffer> NewBuf = check(MemoryBuffer::getFile(TmpName));
if ((*OldBuf)->getBuffer() != NewBuf->getBuffer()) {
OldBuf->reset();
HandleError(errorCodeToError(sys::fs::rename(TmpName, Path)));
}
}
static void parseModuleDefs(StringRef Path) {
@ -640,8 +669,8 @@ filterBitcodeFiles(StringRef Path, std::vector<std::string> &TemporaryFiles) {
log("Creating a temporary archive for " + Path + " to remove bitcode files");
SmallString<128> S;
if (auto EC = sys::fs::createTemporaryFile("lld-" + sys::path::stem(Path),
".lib", S))
if (std::error_code EC = sys::fs::createTemporaryFile(
"lld-" + sys::path::stem(Path), ".lib", S))
fatal("cannot create a temporary file: " + EC.message());
std::string Temp = S.str();
TemporaryFiles.push_back(Temp);

7
lld/test/COFF/unchanged-importlib.test Normal file
View File

@ -0,0 +1,7 @@
# RUN: yaml2obj < %p/Inputs/export.yaml > %t.obj
# RUN: lld-link -out:%t.dll -dll %t.obj
# RUN: touch -t 198002011200.00 %t.lib
# RUN: lld-link -out:%t.dll -dll %t.obj
# RUN: ls -l %t.lib | FileCheck --check-prefix=CHECK %s
# CHECK: Feb 1 1980