Simple GT_NEG optimization for #13837 (#43921)

* Simple arithmetic optimization with GT_NEG

* Skip GT_NEG optimization when an operand is constant. Revert bitwise rotation pattern

* Fixed Value Numbering assert

* Cleaned up code and comments for simple GT_NEG optimization

* Formatting

Co-authored-by: Julie Lee <jeonlee@microsoft.com>

src/coreclr/src/jit/morph.cpp

@@ -13387,6 +13387,56 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac)
 
                 /* No match - exit */
             }
+
+            // Skip optimization if non-NEG operand is constant.
+            // Both op1 and op2 are not constant because it was already checked above.
+            if (opts.OptimizationEnabled() && fgGlobalMorph &&
+                (((op1->gtFlags & GTF_EXCEPT) == 0) || ((op2->gtFlags & GTF_EXCEPT) == 0)))
+            {
+                // a - -b = > a + b
+                // SUB(a, (NEG(b)) => ADD(a, b)
+
+                if (!op1->OperIs(GT_NEG) && op2->OperIs(GT_NEG))
+                {
+                    // tree: SUB
+                    // op1: a
+                    // op2: NEG
+                    // op2Child: b
+
+                    GenTree* op2Child = op2->AsOp()->gtOp1; // b
+                    oper              = GT_ADD;
+                    tree->SetOper(oper, GenTree::PRESERVE_VN);
+                    tree->AsOp()->gtOp2 = op2Child;
+
+                    DEBUG_DESTROY_NODE(op2);
+
+                    op2 = op2Child;
+                }
+
+                // -a - -b = > b - a
+                // SUB(NEG(a), (NEG(b)) => SUB(b, a)
+
+                if (op1->OperIs(GT_NEG) && op2->OperIs(GT_NEG))
+                {
+                    // tree: SUB
+                    // op1: NEG
+                    // op1Child: a
+                    // op2: NEG
+                    // op2Child: b
+
+                    GenTree* op1Child   = op1->AsOp()->gtOp1; // a
+                    GenTree* op2Child   = op2->AsOp()->gtOp1; // b
+                    tree->AsOp()->gtOp1 = op2Child;
+                    tree->AsOp()->gtOp2 = op1Child;
+
+                    DEBUG_DESTROY_NODE(op1);
+                    DEBUG_DESTROY_NODE(op2);
+
+                    op1 = op2Child;
+                    op2 = op1Child;
+                }
+            }
+
             break;
 
 #ifdef TARGET_ARM64
@@ -13555,6 +13605,57 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac)
                         }
                     }
                 }
+
+                if (opts.OptimizationEnabled() && fgGlobalMorph &&
+                    (((op1->gtFlags & GTF_EXCEPT) == 0) || ((op2->gtFlags & GTF_EXCEPT) == 0)))
+                {
+                    // - a + b = > b - a
+                    // ADD((NEG(a), b) => SUB(b, a)
+
+                    // Skip optimization if non-NEG operand is constant.
+                    if (op1->OperIs(GT_NEG) && !op2->OperIs(GT_NEG) &&
+                        !(op2->IsCnsIntOrI() && varTypeIsIntegralOrI(typ)))
+                    {
+                        // tree: ADD
+                        // op1: NEG
+                        // op2: b
+                        // op1Child: a
+
+                        GenTree* op1Child = op1->AsOp()->gtOp1; // a
+                        oper              = GT_SUB;
+                        tree->SetOper(oper, GenTree::PRESERVE_VN);
+                        tree->AsOp()->gtOp1 = op2;
+                        tree->AsOp()->gtOp2 = op1Child;
+
+                        DEBUG_DESTROY_NODE(op1);
+
+                        op1 = op2;
+                        op2 = op1Child;
+                    }
+
+                    // a + -b = > a - b
+                    // ADD(a, (NEG(b)) => SUB(a, b)
+
+                    if (!op1->OperIs(GT_NEG) && op2->OperIs(GT_NEG))
+                    {
+                        // a is non cosntant because it was already canonicalized to have
+                        // variable on the left and constant on the right.
+
+                        // tree: ADD
+                        // op1: a
+                        // op2: NEG
+                        // op2Child: b
+
+                        GenTree* op2Child = op2->AsOp()->gtOp1; // a
+                        oper              = GT_SUB;
+                        tree->SetOper(oper, GenTree::PRESERVE_VN);
+                        tree->AsOp()->gtOp2 = op2Child;
+
+                        DEBUG_DESTROY_NODE(op2);
+
+                        op2 = op2Child;
+                    }
+                }
             }
             /* See if we can fold GT_MUL by const nodes */
             else if (oper == GT_MUL && op2->IsCnsIntOrI() && !optValnumCSE_phase)