[WebAssembly] Elide data segments for .bss sections

Summary:
WebAssembly memories are zero-initialized, so when module does not
import its memory initializing .bss sections is guaranteed to be a
no-op. To reduce binary size and initialization time, .bss sections
are simply not emitted into the final binary unless the memory is
imported.

Reviewers: sbc100

Subscribers: dschuff, jgravelle-google, aheejin, sunfish, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D68965

llvm-svn: 374940

1 files changed, 1 insertions, 0 deletions

diff --git a/lld/wasm/OutputSegment.h b/lld/wasm/OutputSegment.h
index 663a9b82282..06f675c379d 100644
--- a/lld/wasm/OutputSegment.h
+++ b/lld/wasm/OutputSegment.h
@@ -32,6 +32,7 @@ public:
   }
 
   StringRef name;
+  bool isBss = false;
   uint32_t index = 0;
   uint32_t initFlags = 0;
   uint32_t sectionOffset = 0;