Teresa Johnson c81df691f2 [ThinLTO] Avoid temporaries when loading global decl attachment metadata ... When performing ThinLTO importing, the metadata loader attempts to lazy load, by building an index. However, module level global decl attachment metadata was being parsed early while building the index, since the associated (module level) global values aren't materialized on demand. This results in the creation of forward reference temporary metadatas, which are expensive. Normally, these module level global values don't have much attached metadata. However, in the case of -fwhole-program-vtables (e.g. for whole program devirtualization), the vtables may have many attached type metadatas. This was resulting in very slow performance when performing ThinLTO importing with the default lazy loading. This patch restructures the handling of these global decl attachment records, delaying their parsing until after the lazy loading index has been built. Then the parser can use the interface that loads from the index, which resolves forward references immediately instead of creating expensive temporaries. For one ThinLTO backend that imports from modules containing huge numbers of vtables and associated types, I measured the following compile times for the metadata materialization during function importing, rounded to nearest second: No -fwhole-program-vtables: Lazy loading on (head): 1s Lazy loading off (head): 3s Lazy loading on (patch): 1s With -fwhole-program-vtables: Lazy loading on (head): 440s Lazy loading off (head): 4s Lazy loading on (patch): 2s Differential Revision: https://reviews.llvm.org/D87970		2020-09-22 20:32:07 -07:00
..
Reader	[ThinLTO] Avoid temporaries when loading global decl attachment metadata	2020-09-22 20:32:07 -07:00
Writer	Flush bitcode incrementally for LTO output	2020-09-17 03:32:31 +00:00
CMakeLists.txt
LLVMBuild.txt	Update the file headers across all of the LLVM projects in the monorepo	2019-01-19 08:50:56 +00:00