8256058: Improve vector register handling in RegisterMap::pd_location() on x86

Reviewed-by: kvn

Author: Vladimir Ivanov

src/hotspot/cpu/x86/registerMap_x86.cpp

@@ -28,23 +28,35 @@
 
 address RegisterMap::pd_location(VMReg reg) const {
   if (reg->is_XMMRegister()) {
-    int regBase = reg->value() - ConcreteRegisterImpl::max_fpr;
-    if (regBase % 4 == 0) {
-      // Reads of the low and high 16 byte parts should be handled by location itself
-      // because they have separate callee saved entries.
-      // See RegisterSaver::save_live_registers().
-      return NULL;
+    int reg_base = reg->value() - ConcreteRegisterImpl::max_fpr;
+    int base_reg_enc = (reg_base / XMMRegisterImpl::max_slots_per_register);
+    assert(base_reg_enc >= 0 && base_reg_enc < XMMRegisterImpl::number_of_registers, "invalid XMMRegister: %d", base_reg_enc);
+    VMReg base_reg = as_XMMRegister(base_reg_enc)->as_VMReg();
+    intptr_t offset_in_bytes = (reg->value() - base_reg->value()) * VMRegImpl::stack_slot_size;
+    if (base_reg_enc > 15) {
+      if (offset_in_bytes == 0) {
+        return NULL; // ZMM16-31 are stored in full.
+      }
+    } else {
+      if (offset_in_bytes == 0 || offset_in_bytes == 16 || offset_in_bytes == 32) {
+        // Reads of the low and high 16 byte parts should be handled by location itself because
+        // they have separate callee saved entries (see RegisterSaver::save_live_registers()).
+        return NULL;
+      }
+      // The upper part of YMM0-15 and ZMM0-15 registers are saved separately in the frame.
+      if (offset_in_bytes > 32) {
+        base_reg = base_reg->next(8);
+        offset_in_bytes -= 32;
+      } else if (offset_in_bytes > 16) {
+        base_reg = base_reg->next(4);
+        offset_in_bytes -= 16;
+      } else {
+        // XMM0-15 case (0 < offset_in_bytes < 16). No need to adjust base register (or offset).
+      }
     }
-    VMReg baseReg = as_XMMRegister(regBase / XMMRegisterImpl::max_slots_per_register)->as_VMReg();
-    intptr_t offset = (reg->value() - baseReg->value()) * VMRegImpl::stack_slot_size; // offset in bytes
-    if (offset >= 16) {
-      // The high part of YMM registers are saved in a their own area in the frame
-      baseReg = baseReg->next()->next()->next()->next();
-      offset -= 16;
-    }
-    address baseLocation = location(baseReg);
-    if (baseLocation != NULL) {
-      return baseLocation + offset;
+    address base_location = location(base_reg);
+    if (base_location != NULL) {
+      return base_location + offset_in_bytes;
     }
   }
   return NULL;