8337785: Fix simple -Wzero-as-null-pointer-constant warnings in x86 code

Reviewed-by: jwaters, ayang, shade

Author: Kim Barrett

src/hotspot/cpu/x86/frame_x86.cpp

@@ -279,7 +279,7 @@ void frame::patch_pc(Thread* thread, address pc) {
 
   assert(!Continuation::is_return_barrier_entry(*pc_addr), "return barrier");
 
-  assert(_pc == *pc_addr || pc == *pc_addr || *pc_addr == 0, "");
+  assert(_pc == *pc_addr || pc == *pc_addr || *pc_addr == nullptr, "");
   DEBUG_ONLY(address old_pc = _pc;)
   *pc_addr = pc;
   _pc = pc; // must be set before call to get_deopt_original_pc
@@ -483,10 +483,10 @@ frame frame::sender_for_interpreter_frame(RegisterMap* map) const {
 bool frame::is_interpreted_frame_valid(JavaThread* thread) const {
   assert(is_interpreted_frame(), "Not an interpreted frame");
   // These are reasonable sanity checks
-  if (fp() == 0 || (intptr_t(fp()) & (wordSize-1)) != 0) {
+  if (fp() == nullptr || (intptr_t(fp()) & (wordSize-1)) != 0) {
     return false;
   }
-  if (sp() == 0 || (intptr_t(sp()) & (wordSize-1)) != 0) {
+  if (sp() == nullptr || (intptr_t(sp()) & (wordSize-1)) != 0) {
     return false;
   }
   if (fp() + interpreter_frame_initial_sp_offset < sp()) {

src/hotspot/cpu/x86/macroAssembler_x86_sha.cpp

@@ -1,5 +1,5 @@
 /*
-* Copyright (c) 2016, 2021, Intel Corporation. All rights reserved.
+* Copyright (c) 2016, 2024, Intel Corporation. All rights reserved.
 *
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
@@ -689,7 +689,7 @@ void MacroAssembler::sha256_AVX2(XMMRegister msg, XMMRegister state0, XMMRegiste
 
   address K256_W = StubRoutines::x86::k256_W_addr();
   address pshuffle_byte_flip_mask = StubRoutines::x86::pshuffle_byte_flip_mask_addr();
-  address pshuffle_byte_flip_mask_addr = 0;
+  address pshuffle_byte_flip_mask_addr = nullptr;
 
 const XMMRegister& SHUF_00BA        = xmm10;    // ymm10: shuffle xBxA -> 00BA
 const XMMRegister& SHUF_DC00        = xmm12;    // ymm12: shuffle xDxC -> DC00
@@ -1247,7 +1247,7 @@ void MacroAssembler::sha512_AVX2(XMMRegister msg, XMMRegister state0, XMMRegiste
 
     address K512_W = StubRoutines::x86::k512_W_addr();
     address pshuffle_byte_flip_mask_sha512 = StubRoutines::x86::pshuffle_byte_flip_mask_addr_sha512();
-    address pshuffle_byte_flip_mask_addr = 0;
+    address pshuffle_byte_flip_mask_addr = nullptr;
 
     const XMMRegister& XFER = xmm0; // YTMP0
     const XMMRegister& BYTE_FLIP_MASK = xmm9; // ymm9

src/hotspot/cpu/x86/methodHandles_x86.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2024, 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
@@ -572,7 +572,7 @@ void trace_method_handle_stub(const char* adaptername,
 
       frame cur_frame = os::current_frame();
 
-      if (cur_frame.fp() != 0) {  // not walkable
+      if (cur_frame.fp() != nullptr) { // not walkable
 
         // Robust search of trace_calling_frame (independent of inlining).
         // Assumes saved_regs comes from a pusha in the trace_calling_frame.

src/hotspot/cpu/x86/vm_version_x86.cpp

@@ -53,13 +53,13 @@ const char* VM_Version::_features_names[] = { CPU_FEATURE_FLAGS(DECLARE_CPU_FEAT
 #undef DECLARE_CPU_FEATURE_FLAG
 
 // Address of instruction which causes SEGV
-address VM_Version::_cpuinfo_segv_addr = 0;
+address VM_Version::_cpuinfo_segv_addr = nullptr;
 // Address of instruction after the one which causes SEGV
-address VM_Version::_cpuinfo_cont_addr = 0;
+address VM_Version::_cpuinfo_cont_addr = nullptr;
 // Address of instruction which causes APX specific SEGV
-address VM_Version::_cpuinfo_segv_addr_apx = 0;
+address VM_Version::_cpuinfo_segv_addr_apx = nullptr;
 // Address of instruction after the one which causes APX specific SEGV
-address VM_Version::_cpuinfo_cont_addr_apx = 0;
+address VM_Version::_cpuinfo_cont_addr_apx = nullptr;
 
 static BufferBlob* stub_blob;
 static const int stub_size = 2000;

src/hotspot/os_cpu/linux_x86/os_linux_x86.cpp

@@ -224,7 +224,7 @@ bool PosixSignals::pd_hotspot_signal_handler(int sig, siginfo_t* info,
   if (info != nullptr && uc != nullptr && thread != nullptr) {
     pc = (address) os::Posix::ucontext_get_pc(uc);
 
-    if (sig == SIGSEGV && info->si_addr == 0 && info->si_code == SI_KERNEL) {
+    if (sig == SIGSEGV && info->si_addr == nullptr && info->si_code == SI_KERNEL) {
       // An irrecoverable SI_KERNEL SIGSEGV has occurred.
       // It's likely caused by dereferencing an address larger than TASK_SIZE.
       return false;