commit ebb300d0b4340104dcade3afa656a57da2b7660c
author Antonio Sanchez <cantonios@google.com> Sun May 23 12:35:38 2021 -0700
committer Antonio Sanchez <cantonios@google.com> Sun May 23 12:44:37 2021 -0700
tree cf8ddfa15495969e31ff04141cb112bb30fced6f
parent 12471fcb5d59f969c60a9b78727624dc91e5c04e

Modify Unary/Binary/TernaryOp evaluators to work for non-class types.

This used to work for non-class types (e.g. raw function pointers) in
Eigen 3.3.  This was changed in commit 11f55b29 to optimize the
evaluator:

> `sizeof((A-B).cwiseAbs2())` with A,B Vector4f is now 16 bytes, instead of 48 before this optimization.

though I cannot reproduce the 16 byte result.  Both before the change
and after, with multiple compilers/versions, I always get a result of 40 bytes.

https://godbolt.org/z/MsjTc1PGe

This change modifies the code slightly to allow non-class types.  The
final generated code is identical, and the expression remains 40 bytes
for the `abs2` sample case.

Fixes #2251

Eigen/src/Core/CoreEvaluators.h

diff --git a/Eigen/src/Core/CoreEvaluators.h b/Eigen/src/Core/CoreEvaluators.h
index 90c552f..66e030b 100644
--- a/Eigen/src/Core/CoreEvaluators.h
+++ b/Eigen/src/Core/CoreEvaluators.h
@@ -606,13 +606,13 @@
 protected:
 
   // this helper permits to completely eliminate the functor if it is empty
-  class Data : private UnaryOp
+  struct Data
   {
-  public:
     EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE
-    Data(const XprType& xpr) : UnaryOp(xpr.functor()), argImpl(xpr.nestedExpression()) {}
+    Data(const XprType& xpr) : op(xpr.functor()), argImpl(xpr.nestedExpression()) {}
     EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE
-    const UnaryOp& func() const { return static_cast<const UnaryOp&>(*this); }
+    const UnaryOp& func() const { return op; }
+    UnaryOp op;
     evaluator<ArgType> argImpl;
   };
 
@@ -700,12 +700,13 @@
 
 protected:
   // this helper permits to completely eliminate the functor if it is empty
-  struct Data : private TernaryOp
+  struct Data
   {
     EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE
-    Data(const XprType& xpr) : TernaryOp(xpr.functor()), arg1Impl(xpr.arg1()), arg2Impl(xpr.arg2()), arg3Impl(xpr.arg3()) {}
+    Data(const XprType& xpr) : op(xpr.functor()), arg1Impl(xpr.arg1()), arg2Impl(xpr.arg2()), arg3Impl(xpr.arg3()) {}
     EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE
-    const TernaryOp& func() const { return static_cast<const TernaryOp&>(*this); }
+    const TernaryOp& func() const { return op; }
+    TernaryOp op;
     evaluator<Arg1> arg1Impl;
     evaluator<Arg2> arg2Impl;
     evaluator<Arg3> arg3Impl;
@@ -793,12 +794,13 @@
 protected:
 
   // this helper permits to completely eliminate the functor if it is empty
-  struct Data : private BinaryOp
+  struct Data
   {
     EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE
-    Data(const XprType& xpr) : BinaryOp(xpr.functor()), lhsImpl(xpr.lhs()), rhsImpl(xpr.rhs()) {}
+    Data(const XprType& xpr) : op(xpr.functor()), lhsImpl(xpr.lhs()), rhsImpl(xpr.rhs()) {}
     EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE
-    const BinaryOp& func() const { return static_cast<const BinaryOp&>(*this); }
+    const BinaryOp& func() const { return op; }
+    BinaryOp op;
     evaluator<Lhs> lhsImpl;
     evaluator<Rhs> rhsImpl;
   };
@@ -858,12 +860,13 @@
 protected:
 
   // this helper permits to completely eliminate the functor if it is empty
-  struct Data : private UnaryOp
+  struct Data
   {
     EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE
-    Data(const XprType& xpr) : UnaryOp(xpr.functor()), argImpl(xpr.nestedExpression()) {}
+    Data(const XprType& xpr) : op(xpr.functor()), argImpl(xpr.nestedExpression()) {}
     EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE
-    const UnaryOp& func() const { return static_cast<const UnaryOp&>(*this); }
+    const UnaryOp& func() const { return op; }
+    UnaryOp op;
     evaluator<ArgType> argImpl;
   };