From 26275b250a271b27132e41486de5bb5b18e8365a Mon Sep 17 00:00:00 2001
From: Benoit Jacob <benoitjacob@google.com>
Date: Mon, 23 Feb 2015 16:55:17 -0500
Subject: [PATCH] Fix my recent prefetch changes:  - the first prefetch is
 actually harmful on Haswell with FMA,    but it is the most beneficial on
 ARM.  - the second prefetch... I was very stupid and multiplied by
 sizeof(scalar)    and offset of a scalar* pointer. The old offset was 64; pk
 = 8, so 64=pk*8.    So this effectively restores the older offset. Actually,
 there were    two prefetches here, one with offset 48 and one with offset 64.
 I could not    confirm any benefit from this strange 48 offset on either the
 haswell or    my ARM device.

---
 Eigen/src/Core/products/GeneralBlockPanelKernel.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Eigen/src/Core/products/GeneralBlockPanelKernel.h b/Eigen/src/Core/products/GeneralBlockPanelKernel.h
index ccd906540..93bd6ab53 100644
--- a/Eigen/src/Core/products/GeneralBlockPanelKernel.h
+++ b/Eigen/src/Core/products/GeneralBlockPanelKernel.h
@@ -855,7 +855,7 @@ void gebp_kernel<LhsScalar,RhsScalar,Index,DataMapper,mr,nr,ConjugateLhs,Conjuga
               EIGEN_ASM_COMMENT("begin step of gebp micro kernel 3pX4"); \
               EIGEN_ASM_COMMENT("Note: these asm comments work around bug 935!"); \
               internal::prefetch(blA+(3*K+16)*LhsProgress); \
-              internal::prefetch(blB+(4*K+16)*RhsProgress); /* Bug 953 */ \
+              if (EIGEN_ARCH_ARM) internal::prefetch(blB+(4*K+16)*RhsProgress); /* Bug 953 */ \
               traits.loadLhs(&blA[(0+3*K)*LhsProgress], A0);  \
               traits.loadLhs(&blA[(1+3*K)*LhsProgress], A1);  \
               traits.loadLhs(&blA[(2+3*K)*LhsProgress], A2);  \
@@ -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 + 4 * pk * sizeof(RhsScalar)); /* Bug 953 */
+            internal::prefetch(blB + 8 * pk); /* Bug 953 */
             EIGEN_GEBP_ONESTEP(0);
             EIGEN_GEBP_ONESTEP(1);
             EIGEN_GEBP_ONESTEP(2);