Refactored SymbolInfo to lower memory usage in RTS

Previously as part of #11223 a new struct `SymbolInfo` was introduced to
keep track it the weak symbol status of a symbol.

This structure also kept a copy of the calculated address of the symbol
which turns out was useful in ignoring non-weak zero-valued symbols.

The information was kept in an array so it means for every symbol two
extra bytes were kept even though the vast majority of symbols are
non-weak and non-zero valued.

This changes the array into a sparse map keeping this information only
for the symbols that are weak or zero-valued. This allows for a
reduction in the amount of information needed to be kept while giving up
a small (negligable) hit in performance as this information now has to
be looked up in hashmaps.

Test Plan: ./validate on all platforms that use the runtime linker.

For unix platforms please ensure `DYNAMIC_GHC_PROGRAMS=NO` is added to
your validate file.

Reviewers: simonmar, austin, erikd, bgamari

Reviewed By: simonmar, bgamari

Subscribers: thomie, #ghc_windows_task_force

Differential Revision: https://phabricator.haskell.org/D2184

GHC Trac Issues: #11816

1 files changed, 17 insertions, 0 deletions

diff --git a/rts/RtsSymbolInfo.h b/rts/RtsSymbolInfo.h
new file mode 100644
index 0000000000..6987183d2a
--- /dev/null
+++ b/rts/RtsSymbolInfo.h
@@ -0,0 +1,17 @@
+/* -----------------------------------------------------------------------------
+ *
+ * (c) The GHC Team, 2000-2015
+ *
+ * RTS Symbol Info
+ *
+ * ---------------------------------------------------------------------------*/
+
+#ifndef RTS_SYMBOLINFO_H
+#define RTS_SYMBOLINFO_H
+
+#include "LinkerInternals.h"
+
+HsBool isSymbolWeak(ObjectCode *owner, void *label);
+void setWeakSymbol(ObjectCode *owner, void *label);
+
+#endif /* RTS_SYMBOLINFO_H */