From f886ff7b417739cf2269267e7b057a7cfdc85324 Mon Sep 17 00:00:00 2001
From: Cherry Zhang <cherryyz@google.com>
Date: Tue, 28 Apr 2020 18:59:57 -0400
Subject: [PATCH] [dev.link] cmd/link: free loader memory after LoadFull
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After LoadFull, we'll be using sym.Symbols mostly. We still need
the loader information for symbol index mappings and name
lookups, but not much else. Free some memory.

Linking cmd/compile,

name           old time/op    new time/op    delta
Loadlibfull_GC    44.5M ± 0%     35.8M ± 0%    -19.66%  (p=0.008 n=5+5)
Archive_GC        46.4M ± 0%     37.6M ± 0%    -18.89%  (p=0.008 n=5+5)

Linking cmd/compile with external linking,

name           old time/op    new time/op    delta
Loadlibfull_GC    82.5M ± 0%     57.4M ± 0%    -30.41%  (p=0.008 n=5+5)
Archive_GC        86.8M ± 0%     61.7M ± 0%    -28.90%  (p=0.008 n=5+5)

Change-Id: I6859d488172ef8968918b86de527fbfed6832ebf
Reviewed-on: https://go-review.googlesource.com/c/go/+/230300
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
---
 src/cmd/link/internal/ld/pe.go         |  2 +-
 src/cmd/link/internal/loader/loader.go | 32 ++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/src/cmd/link/internal/ld/pe.go b/src/cmd/link/internal/ld/pe.go
index 547200fbee..362d2fd0a5 100644
--- a/src/cmd/link/internal/ld/pe.go
+++ b/src/cmd/link/internal/ld/pe.go
@@ -1130,7 +1130,7 @@ func addimports(ctxt *Link, datsect *peSection) {
 		for m := d.ms; m != nil; m = m.next {
 			m.off = uint64(pefile.nextSectOffset) + uint64(ctxt.Out.Offset()) - uint64(startoff)
 			ctxt.Out.Write16(0) // hint
-			strput(ctxt.Out, ldr.SymExtname(m.s))
+			strput(ctxt.Out, ldr.Syms[m.s].Extname())
 		}
 	}
 
diff --git a/src/cmd/link/internal/loader/loader.go b/src/cmd/link/internal/loader/loader.go
index e3dec5feee..a6d9417c00 100644
--- a/src/cmd/link/internal/loader/loader.go
+++ b/src/cmd/link/internal/loader/loader.go
@@ -2124,6 +2124,38 @@ func (l *Loader) LoadFull(arch *sys.Arch, syms *sym.Symbols, needReloc bool) {
 			}
 		}
 	}
+
+	// Free some memory.
+	// At this point we still need basic index mapping, and some fields of
+	// external symbol payloads, but not much else.
+	l.values = nil
+	l.symSects = nil
+	l.outdata = nil
+	l.itablink = nil
+	l.attrOnList = nil
+	l.attrLocal = nil
+	l.attrNotInSymbolTable = nil
+	l.attrVisibilityHidden = nil
+	l.attrDuplicateOK = nil
+	l.attrShared = nil
+	l.attrExternal = nil
+	l.attrReadOnly = nil
+	l.attrTopFrame = nil
+	l.attrSpecial = nil
+	l.attrCgoExportDynamic = nil
+	l.attrCgoExportStatic = nil
+	l.outer = nil
+	l.align = nil
+	l.dynimplib = nil
+	l.dynimpvers = nil
+	l.localentry = nil
+	l.extname = nil
+	l.elfType = nil
+	l.plt = nil
+	l.got = nil
+	l.dynid = nil
+	l.relocVariant = nil
+	l.extRelocs = nil
 }
 
 // ResolveABIAlias given a symbol returns the ABI alias target of that