From 692136350becc4e0b4dce077c2f1e201f18af62d Mon Sep 17 00:00:00 2001
From: Benoit Jacob <benoitjacob@google.com>
Date: Wed, 25 Feb 2015 12:37:14 -0500
Subject: [PATCH] So I extensively measured the impact of the offset in this
 prefetch. I tried offset values from 0 to 128 (on this float* pointer, so
 implicitly times 4 bytes).

On x86, I tested a Sandy Bridge with AVX with 12M cache and a Haswell with AVX+FMA with 6M cache on MatrixXf sizes up to 2400.

I could not see any significant impact of this offset.

On Nexus 5, the offset has a slight effect: values around 32 (times sizeof float) are worst. Anything else is the same: the current 64 (8*pk), or... 0.

So let's just go with 0!

Note that we needed a fix anyway for not accounting for the value of RhsProgress. 0 nicely avoids the issue altogether!
---
 Eigen/src/Core/products/GeneralBlockPanelKernel.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Eigen/src/Core/products/GeneralBlockPanelKernel.h b/Eigen/src/Core/products/GeneralBlockPanelKernel.h
index 93bd6ab53..0890bc690 100644
--- a/Eigen/src/Core/products/GeneralBlockPanelKernel.h
+++ b/Eigen/src/Core/products/GeneralBlockPanelKernel.h
@@ -878,7 +878,7 @@ void gebp_kernel<LhsScalar,RhsScalar,Index,DataMapper,mr,nr,ConjugateLhs,Conjuga
               EIGEN_ASM_COMMENT("end step of gebp micro kernel 3pX4"); \
             } while(false)
 
-            internal::prefetch(blB + 8 * pk); /* Bug 953 */
+            internal::prefetch(blB);
             EIGEN_GEBP_ONESTEP(0);
             EIGEN_GEBP_ONESTEP(1);
             EIGEN_GEBP_ONESTEP(2);