This adds support for generating Chrome-tracing .json profile traces in the LLD COFF driver. Also add the necessary time scopes, so that the profile trace shows in great detail which tasks are executed. As an example, this is what we see when linking a Unreal Engine executable: 
Identified with readability-qualified-auto.
The construction was explained in https://reviews.llvm.org/D44810?id=139526#inline-391999 but reading the code shouldn't require hunting down old reviews to understand it. The precomputed list was missing an entry for the empty list case, and one entry at the very end. (The current last entry is the last one where 3 * BucketCount fits in a signed int, but the reference implementation uses unsigneds as far as I can tell, so there's room for one more entry.) No behavior change for inputs seen in practice. Differential Revision: https://reviews.llvm.org/D64738 llvm-svn: 366107
lld-link used to write PDB files that DIA couldn't recover natvis files from if: - The global strings table was > 64kiB - There were at least 3 natvis files The cause was that the hash function for the /src/headerblock stream was incorrect: It needs to be truncated to 16 bit. If the global strings table was <= 64kiB, truncating to 16 bit is a no-op, so this wasn't needed for small programs. If there are only 1 or 2 natvis files, then the growth strategy in HashTable::grow() would mean the hash table would have 2 buckets (for 1 natvis file) or 4 buckets (for 4 natvis files), and since the hash function is used modulo number of buckets, and since 2 and 4 divide 0x10000, the missing `% 0x10000` is a no-op there too. For 3 natvis files, the hash table grows to 6 buckets, which has a factor that's not common with 0x10000 and the difference starts to matter. Fixes PR41626. Differential Revision: https://reviews.llvm.org/D61277 llvm-svn: 359515
This avoids allocating a few KB of heap memory on startup, and instead allocates these maps lazily. I noticed this while profiling LLD. llvm-svn: 357192
to reflect the new license. We understand that people may be surprised that we're moving the header entirely to discuss the new license. We checked this carefully with the Foundation's lawyer and we believe this is the correct approach. Essentially, all code in the project is now made available by the LLVM project under our new license, so you will see that the license headers include that license only. Some of our contributors have contributed code under our old license, and accordingly, we have retained a copy of our old license notice in the top-level files in each project and repository. llvm-svn: 351636
This was reverted several times due to what ultimately turned out to be incompatibilities in our serialized hash table format. Several changes went in prior to this to fix those issues since they were more fundamental and independent of supporting injected sources, so now that those are fixed this change should hopefully pass. llvm-svn: 328363
When investigating bugs in PDB generation, the first step is often to do the same link with link.exe and then compare PDBs. But comparing PDBs is hard because two completely different byte sequences can both be correct, so it hampers the investigation when you also have to spend time figuring out not just which bytes are different, but also if the difference is meaningful. This patch fixes a couple of cases related to string table emission, hash table emission, and the order in which we emit strings that makes more of our bytes the same as the bytes generated by MS PDBs. Differential Revision: https://reviews.llvm.org/D44810 llvm-svn: 328348
NFC, this just renames some methods to better express what they do, and also adds a few helper methods to add some symmetry to the API in a few places (for example there was a getStringFromId but not a getIdFromString method in the string table). llvm-svn: 328221