JIT: Remove reference to "CSE candidate" in morph (dotnet#110218)

CSE no longer reinvokes morph, and the checks for CSE were removed in
07f15ef. However, a few comments were left over, so clean those up.

src/coreclr/jit/morph.cpp

@@ -7538,8 +7538,7 @@ GenTreeOp* Compiler::fgMorphCommutative(GenTreeOp* tree)
     {
         // Since 'tree->gtGetOp1()' can have complex structure (e.g. COMMA(..(COMMA(..,op1)))
         // don't run the optimization for such trees outside of global morph.
-        // Otherwise, there is a chance of violating VNs invariants and/or modifying a tree
-        // that is an active CSE candidate.
+        // Otherwise, there is a chance of violating VNs invariants.
         return nullptr;
     }
 
@@ -8395,7 +8394,6 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac, bool* optA
 
         case GT_EQ:
         case GT_NE:
-            // It is not safe to reorder/delete CSE's
             if (op2->IsIntegralConst())
             {
                 tree = fgOptimizeEqualityComparisonWithConst(tree->AsOp());
@@ -8430,7 +8428,6 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac, bool* optA
                 op2  = tree->gtGetOp2();
             }
 
-            // op2's value may be changed, so it cannot be a CSE candidate.
             if (op2->IsIntegralConst())
             {
                 tree = fgOptimizeRelationalComparisonWithConst(tree->AsOp());
@@ -8483,9 +8480,6 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac, bool* optA
                 goto CM_OVF_OP;
             }
 
-            // TODO #4104: there are a lot of other places where
-            // this condition is not checked before transformations.
-            noway_assert(op2);
             if (fgGlobalMorph && !op2->TypeIs(TYP_BYREF))
             {
                 /* Check for "op1 - cns2" , we change it to "op1 + (-cns2)" */
@@ -8668,10 +8662,6 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac, bool* optA
         case GT_NOT:
         case GT_NEG:
             // Remove double negation/not.
-            // Note: this is not a safe transformation if "tree" is a CSE candidate.
-            // Consider for example the following expression: NEG(NEG(OP)), where any
-            // NEG is a CSE candidate. Were we to morph this to just OP, CSE would fail to find
-            // the original NEG in the statement.
             if (op1->OperIs(oper) && opts.OptimizationEnabled())
             {
                 JITDUMP("Remove double negation/not\n")
@@ -8959,9 +8949,7 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac, bool* optA
 
     assert(oper == tree->gtOper);
 
-    // Propagate comma throws.
-    // If we are in the Valuenum CSE phase then don't morph away anything as these
-    // nodes may have CSE defs/uses in them.
+    // Propagate comma throws. Only done in global morph since this does not preserve VNs.
     if (fgGlobalMorph && (oper != GT_COLON) &&
         /* TODO-ASG-Cleanup: delete this zero-diff quirk */ !GenTree::OperIsStore(oper))
     {
@@ -10358,8 +10346,7 @@ GenTree* Compiler::fgOptimizeHWIntrinsicAssociative(GenTreeHWIntrinsic* tree)
     {
         // Since 'tree->Op(1)' can have complex structure; e.g. `(.., (.., op1))`
         // don't run the optimization for such trees outside of global morph.
-        // Otherwise, there is a chance of violating VNs invariants and/or modifying a tree
-        // that is an active CSE candidate.
+        // Otherwise, there is a chance of violating VNs invariants.
         return nullptr;
     }