8370666: VectorAPI: Add clear comments for vector relative code in c2

src/hotspot/share/opto/matcher.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -327,6 +327,8 @@ class Matcher : public PhaseTransform {
   // e.g. Op_ vector nodes and other intrinsics while guarding with vlen
   static bool match_rule_supported_vector(int opcode, int vlen, BasicType bt);
 
+  // Returns true if the platform efficiently implements the given masked vector
+  // operation using predicate features, false otherwise.
   static bool match_rule_supported_vector_masked(int opcode, int vlen, BasicType bt);
 
   // Determines if a vector operation needs to be partially implemented with a mask

src/hotspot/share/opto/node.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2026, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2024, 2025, Alibaba Group Holding Limited. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
@@ -843,7 +843,8 @@ class Node {
     Flag_has_swapped_edges           = 1ULL << 11,
     Flag_is_scheduled                = 1ULL << 12,
     Flag_is_expensive                = 1ULL << 13,
-    Flag_is_predicated_vector        = 1ULL << 14,
+    Flag_is_predicated_vector        = 1ULL << 14, // Marked on a vector node that has an additional
+                                                   // mask input controlling the lane operations.
     Flag_for_post_loop_opts_igvn     = 1ULL << 15,
     Flag_for_merge_stores_igvn       = 1ULL << 16,
     Flag_is_removed_by_peephole      = 1ULL << 17,

src/hotspot/share/opto/type.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -2443,6 +2443,12 @@ const TypeVect* TypeVect::make(BasicType elem_bt, uint length, bool is_mask) {
   return nullptr;
 }
 
+// Create a vector mask type with the given element basic type and length.
+// - Returns "TypeVectMask" (PVectMask) for platforms that support the predicate
+//   feature and it is implemented properly in the backend, allowing the mask to
+//   be stored in a predicate/mask register.
+// - Returns a normal vector type "TypeVectA ~ TypeVectZ" (NVectMask) otherwise,
+//   where the vector mask is stored in a vector register.
 const TypeVect* TypeVect::makemask(BasicType elem_bt, uint length) {
   if (Matcher::has_predicated_vectors() &&
       Matcher::match_rule_supported_vector_masked(Op_VectorLoadMask, length, elem_bt)) {

src/hotspot/share/opto/type.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -1012,7 +1012,7 @@ class TypeAry : public Type {
 };
 
 //------------------------------TypeVect---------------------------------------
-// Class of Vector Types
+// Basic class of vector (mask) types.
 class TypeVect : public Type {
   const BasicType _elem_bt;  // Vector's element type
   const uint _length;  // Elements in vector (power of 2)
@@ -1052,6 +1052,16 @@ class TypeVect : public Type {
 #endif
 };
 
+// TypeVect subclasses representing vectors or vector masks with "BVectMask" or "NVectMask"
+// layout (see vectornode.hpp for detailed notes on vector mask representations), mapped
+// to vector registers and distinguished by vector register size:
+//
+// - TypeVectA: Scalable vector type (variable size, e.g., AArch64 SVE, RISC-V RVV)
+// - TypeVectS: 32-bit vector type
+// - TypeVectD: 64-bit vector type
+// - TypeVectX: 128-bit vector type
+// - TypeVectY: 256-bit vector type
+// - TypeVectZ: 512-bit vector type
 class TypeVectA : public TypeVect {
   friend class TypeVect;
   TypeVectA(BasicType elem_bt, uint length) : TypeVect(VectorA, elem_bt, length) {}
@@ -1082,6 +1092,9 @@ class TypeVectZ : public TypeVect {
   TypeVectZ(BasicType elem_bt, uint length) : TypeVect(VectorZ, elem_bt, length) {}
 };
 
+// Class of TypeVectMask, representing vector masks with "PVectMask" layout (see
+// vectornode.hpp for detailed notes on vector mask representations), mapped to
+// dedicated hardware predicate/mask registers.
 class TypeVectMask : public TypeVect {
 public:
   friend class TypeVect;