From e686d8dc6cd67c35132059d0718d1501f0af1e67 Mon Sep 17 00:00:00 2001
From: Simon Marlow <simonmarhaskell@gmail.com>
Date: Wed, 16 Apr 2008 23:24:33 +0000
Subject: [PATCH] pad step_workspace to 64 bytes, to speed up access to
 gct->steps[]

---
 includes/Rts.h    |    6 ++++++
 rts/sm/GC.c       |    3 +++
 rts/sm/GCThread.h |    6 +++++-
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/includes/Rts.h b/includes/Rts.h
index ec84ed9..1d455f0 100644
--- a/includes/Rts.h
+++ b/includes/Rts.h
@@ -38,6 +38,12 @@ extern "C" {
 #define FLEXIBLE_ARRAY 0
 #endif
 
+#if __GNUC__ >= 3
+#define ATTRIBUTE_ALIGNED(n) __attribute__((aligned(n)))
+#else
+#define ATTRIBUTE_ALIGNED(n) /*nothing*/
+#endif
+
 /* Fix for mingw stat problem (done here so it's early enough) */
 #ifdef mingw32_HOST_OS
 #define __MSVCRT__ 1
diff --git a/rts/sm/GC.c b/rts/sm/GC.c
index 8bdea7d..2b6dbb7 100644
--- a/rts/sm/GC.c
+++ b/rts/sm/GC.c
@@ -203,6 +203,9 @@ GarbageCollect ( rtsBool force_major_gc )
   }
 #endif
 
+  ASSERT(sizeof(step_workspace) == 16 * sizeof(StgWord));
+  // otherwise adjust the padding in step_workspace.
+
   // tell the stats department that we've started a GC 
   stat_startGC();
 
diff --git a/rts/sm/GCThread.h b/rts/sm/GCThread.h
index 8d171ae..338cca7 100644
--- a/rts/sm/GCThread.h
+++ b/rts/sm/GCThread.h
@@ -95,7 +95,11 @@ typedef struct step_workspace_ {
     bdescr *     part_list;
     unsigned int n_part_blocks;      // count of above
 
-} step_workspace;
+    StgWord pad[5];
+
+} step_workspace ATTRIBUTE_ALIGNED(64);
+// align so that computing gct->steps[n] is a shift, not a multiply
+// fails if the size is <64, which is why we need the pad above
 
 /* ----------------------------------------------------------------------------
    GC thread object
-- 
1.7.10.4