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diff --git a/openpower/sv/overview.mdwn b/openpower/sv/overview.mdwn
index c89d0995b85b5eef55aa0ec092800e17dc411116..baa58fdd79df5938b4872354a8aaa53bc7398f41 100644 (file)
--- a/openpower/sv/overview.mdwn
+++ b/openpower/sv/overview.mdwn
@@ -408,6 +408,9 @@ is applied to the whole subvector:
         if (RA.isvec)  { irs1 += 1; }
         if (RB.isvec)  { irs2 += 1; }
 
+The primary reason for this is because Shader Compilers treat vec2/3/4 as
+"single units".  Recognising this in hardware is just sensible.
+
 # Swizzle <a name="swizzle"></a>
 
 Swizzle is particularly important for 3D work.  It allows in-place