8371388: [BACKOUT] JDK-8365047: Remove exception handler stub code in C2

Reviewed-by: chagedorn, epeter

Author: TobiHartmann

src/hotspot/cpu/aarch64/aarch64.ad

@@ -1,7 +1,6 @@
 //
 // Copyright (c) 2003, 2025, Oracle and/or its affiliates. All rights reserved.
 // Copyright (c) 2014, 2024, Red Hat, Inc. All rights reserved.
-// Copyright 2025 Arm Limited and/or its affiliates.
 // DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 //
 // This code is free software; you can redistribute it and/or modify it
@@ -1195,10 +1194,15 @@ class HandlerImpl {
 
  public:
 
+  static int emit_exception_handler(C2_MacroAssembler *masm);
   static int emit_deopt_handler(C2_MacroAssembler* masm);
 
+  static uint size_exception_handler() {
+    return MacroAssembler::far_codestub_branch_size();
+  }
+
   static uint size_deopt_handler() {
-    // count one branch instruction and one far call instruction sequence
+    // count one adr and one far branch instruction
     return NativeInstruction::instruction_size + MacroAssembler::far_codestub_branch_size();
   }
 };
@@ -2257,6 +2261,25 @@ uint MachUEPNode::size(PhaseRegAlloc* ra_) const
 
 //=============================================================================
 
+// Emit exception handler code.
+int HandlerImpl::emit_exception_handler(C2_MacroAssembler* masm)
+{
+  // mov rscratch1 #exception_blob_entry_point
+  // br rscratch1
+  // Note that the code buffer's insts_mark is always relative to insts.
+  // That's why we must use the macroassembler to generate a handler.
+  address base = __ start_a_stub(size_exception_handler());
+  if (base == nullptr) {
+    ciEnv::current()->record_failure("CodeCache is full");
+    return 0;  // CodeBuffer::expand failed
+  }
+  int offset = __ offset();
+  __ far_jump(RuntimeAddress(OptoRuntime::exception_blob()->entry_point()));
+  assert(__ offset() - offset <= (int) size_exception_handler(), "overflow");
+  __ end_a_stub();
+  return offset;
+}
+
 // Emit deopt handler code.
 int HandlerImpl::emit_deopt_handler(C2_MacroAssembler* masm)
 {
@@ -2267,18 +2290,14 @@ int HandlerImpl::emit_deopt_handler(C2_MacroAssembler* masm)
     ciEnv::current()->record_failure("CodeCache is full");
     return 0;  // CodeBuffer::expand failed
   }
-
   int offset = __ offset();
-  Label start;
-  __ bind(start);
-  __ far_call(RuntimeAddress(SharedRuntime::deopt_blob()->unpack()));
 
-  int entry_offset = __ offset();
-  __ b(start);
+  __ adr(lr, __ pc());
+  __ far_jump(RuntimeAddress(SharedRuntime::deopt_blob()->unpack()));
 
   assert(__ offset() - offset == (int) size_deopt_handler(), "overflow");
   __ end_a_stub();
-  return entry_offset;
+  return offset;
 }
 
 // REQUIRED MATCHER CODE

src/hotspot/cpu/aarch64/c1_LIRAssembler_aarch64.cpp

@@ -449,18 +449,12 @@ int LIR_Assembler::emit_deopt_handler() {
 
   int offset = code_offset();
 
-  Label start;
-  __ bind(start);
-
-  __ far_call(RuntimeAddress(SharedRuntime::deopt_blob()->unpack()));
-
-  int entry_offset = __ offset();
-  __ b(start);
-
+  __ adr(lr, pc());
+  __ far_jump(RuntimeAddress(SharedRuntime::deopt_blob()->unpack()));
   guarantee(code_offset() - offset <= deopt_handler_size(), "overflow");
   __ end_a_stub();
 
-  return entry_offset;
+  return offset;
 }
 
 void LIR_Assembler::add_debug_info_for_branch(address adr, CodeEmitInfo* info) {

src/hotspot/cpu/aarch64/c1_LIRAssembler_aarch64.hpp

@@ -71,7 +71,7 @@ friend class ArrayCopyStub;
     //            CompiledDirectCall::to_trampoline_stub_size()
     _call_stub_size = 13 * NativeInstruction::instruction_size,
     _exception_handler_size = DEBUG_ONLY(1*K) NOT_DEBUG(175),
-    _deopt_handler_size = 4 * NativeInstruction::instruction_size
+    _deopt_handler_size = 7 * NativeInstruction::instruction_size
   };
 
 public:

src/hotspot/cpu/aarch64/nativeInst_aarch64.cpp

@@ -394,6 +394,12 @@ void NativePostCallNop::make_deopt() {
   NativeDeoptInstruction::insert(addr_at(0));
 }
 
+#ifdef ASSERT
+static bool is_movk_to_zr(uint32_t insn) {
+  return ((insn & 0xffe0001f) == 0xf280001f);
+}
+#endif
+
 bool NativePostCallNop::patch(int32_t oopmap_slot, int32_t cb_offset) {
   if (((oopmap_slot & 0xff) != oopmap_slot) || ((cb_offset & 0xffffff) != cb_offset)) {
     return false; // cannot encode

src/hotspot/cpu/aarch64/nativeInst_aarch64.hpp

@@ -526,24 +526,14 @@ inline NativeLdSt* NativeLdSt_at(address addr) {
 // can store an offset from the initial nop to the nmethod.
 
 class NativePostCallNop: public NativeInstruction {
-private:
-  static bool is_movk_to_zr(uint32_t insn) {
-    return ((insn & 0xffe0001f) == 0xf280001f);
-  }
-
 public:
   bool check() const {
-    // Check the first instruction is NOP.
-    if (is_nop()) {
-      uint32_t insn = *(uint32_t*)addr_at(4);
-      // Check next instruction is MOVK zr, xx.
-      // These instructions only ever appear together in a post-call
-      // NOP, so it's unnecessary to check that the third instruction is
-      // a MOVK as well.
-      return is_movk_to_zr(insn);
-    }
-
-    return false;
+    uint64_t insns = *(uint64_t*)addr_at(0);
+    // Check for two instructions: nop; movk zr, xx
+    // These instructions only ever appear together in a post-call
+    // NOP, so it's unnecessary to check that the third instruction is
+    // a MOVK as well.
+    return (insns & 0xffe0001fffffffff) == 0xf280001fd503201f;
   }
 
   bool decode(int32_t& oopmap_slot, int32_t& cb_offset) const {

src/hotspot/cpu/aarch64/runtime_aarch64.cpp

@@ -260,6 +260,8 @@ UncommonTrapBlob* OptoRuntime::generate_uncommon_trap_blob() {
 
 //------------------------------generate_exception_blob---------------------------
 // creates exception blob at the end
+// Using exception blob, this code is jumped from a compiled method.
+// (see emit_exception_handler in aarch64.ad file)
 //
 // Given an exception pc at a call we call into the runtime for the
 // handler in this method. This handler might merely restore state

src/hotspot/cpu/arm/arm.ad

@@ -105,8 +105,14 @@ class HandlerImpl {
 
  public:
 
+  static int emit_exception_handler(C2_MacroAssembler *masm);
   static int emit_deopt_handler(C2_MacroAssembler* masm);
 
+  static uint size_exception_handler() {
+    return ( 3 * 4 );
+  }
+
+
   static uint size_deopt_handler() {
     return ( 9 * 4 );
   }
@@ -870,6 +876,26 @@ uint MachUEPNode::size(PhaseRegAlloc *ra_) const {
 
 //=============================================================================
 
+// Emit exception handler code.
+int HandlerImpl::emit_exception_handler(C2_MacroAssembler* masm) {
+  address base = __ start_a_stub(size_exception_handler());
+  if (base == nullptr) {
+    ciEnv::current()->record_failure("CodeCache is full");
+    return 0;  // CodeBuffer::expand failed
+  }
+
+  int offset = __ offset();
+
+  // OK to trash LR, because exception blob will kill it
+  __ jump(OptoRuntime::exception_blob()->entry_point(), relocInfo::runtime_call_type, LR_tmp);
+
+  assert(__ offset() - offset <= (int) size_exception_handler(), "overflow");
+
+  __ end_a_stub();
+
+  return offset;
+}
+
 int HandlerImpl::emit_deopt_handler(C2_MacroAssembler* masm) {
   // Can't use any of the current frame's registers as we may have deopted
   // at a poll and everything can be live.
@@ -880,26 +906,19 @@ int HandlerImpl::emit_deopt_handler(C2_MacroAssembler* masm) {
   }
 
   int offset = __ offset();
+  address deopt_pc = __ pc();
 
-  Label start;
-  __ bind(start);
-
+  __ sub(SP, SP, wordSize); // make room for saved PC
+  __ push(LR); // save LR that may be live when we get here
+  __ mov_relative_address(LR, deopt_pc);
+  __ str(LR, Address(SP, wordSize)); // save deopt PC
+  __ pop(LR); // restore LR
   __ jump(SharedRuntime::deopt_blob()->unpack(), relocInfo::runtime_call_type, noreg);
 
-  int entry_offset = __ offset();
-  address deopt_pc = __ pc();
-  // Preserve R0 and reserve space for the address of the entry point
-  __ push(RegisterSet(R0) | RegisterSet(R1));
-  // Store the entry point address
-  __ mov_relative_address(R0, deopt_pc);
-  __ str(R0, Address(SP, wordSize));
-  __ pop(R0); // restore R0
-  __ b(start);
-
   assert(__ offset() - offset <= (int) size_deopt_handler(), "overflow");
 
   __ end_a_stub();
-  return entry_offset;
+  return offset;
 }
 
 bool Matcher::match_rule_supported(int opcode) {

src/hotspot/cpu/arm/c1_LIRAssembler_arm.cpp

@@ -272,20 +272,14 @@ int LIR_Assembler::emit_deopt_handler() {
 
   int offset = code_offset();
 
-  Label start;
-  __ bind(start);
-
-  __ jump(SharedRuntime::deopt_blob()->unpack(), relocInfo::runtime_call_type, noreg);
-
-  int entry_offset = __ offset();
   __ mov_relative_address(LR, __ pc());
   __ push(LR); // stub expects LR to be saved
-  __ b(start);
+  __ jump(SharedRuntime::deopt_blob()->unpack(), relocInfo::runtime_call_type, noreg);
 
   assert(code_offset() - offset <= deopt_handler_size(), "overflow");
   __ end_a_stub();
 
-  return entry_offset;
+  return offset;
 }
 
 

src/hotspot/cpu/arm/c1_LIRAssembler_arm.hpp

@@ -54,7 +54,7 @@
   enum {
     _call_stub_size = 16,
     _exception_handler_size = PRODUCT_ONLY(68) NOT_PRODUCT(68+60),
-    _deopt_handler_size = 20
+    _deopt_handler_size = 16
   };
 
  public:

src/hotspot/cpu/arm/runtime_arm.cpp

@@ -182,6 +182,8 @@ UncommonTrapBlob* OptoRuntime::generate_uncommon_trap_blob() {
 
 //------------------------------ generate_exception_blob ---------------------------
 // creates exception blob at the end
+// Using exception blob, this code is jumped from a compiled method.
+// (see emit_exception_handler in sparc.ad file)
 //
 // Given an exception pc at a call we call into the runtime for the
 // handler in this method. This handler might merely restore state