From 759599553bab6c95399253ba366a0f5b1b3dd48f Mon Sep 17 00:00:00 2001
From: Andrew Waterman <andrew@sifive.com>
Date: Fri, 31 May 2024 01:24:02 -0700
Subject: Avoid checking ELP before every instruction fetch

Serialize after setting ELP.  That way, we can hoist the check
outside of the main simulation loop.
---
 riscv/execute.cc     |  4 ++--
 riscv/insns/c_jalr.h |  1 +
 riscv/insns/c_jr.h   |  1 +
 riscv/insns/jalr.h   |  1 +
 riscv/processor.cc   | 16 ++++++----------
 riscv/processor.h    |  2 +-
 6 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/riscv/execute.cc b/riscv/execute.cc
index b2532c9..f263dce 100644
--- a/riscv/execute.cc
+++ b/riscv/execute.cc
@@ -247,6 +247,8 @@ void processor_t::step(size_t n)
     {
       take_pending_interrupt();
 
+      check_if_lpad_required();
+
       if (unlikely(slow_path()))
       {
         // Main simulation loop, slow path.
@@ -280,7 +282,6 @@ void processor_t::step(size_t n)
 
           in_wfi = false;
           insn_fetch_t fetch = mmu->load_insn(pc);
-          execute_insn_prehook(fetch.insn);
           if (debug && !state.serialized)
             disasm(fetch.insn);
           pc = execute_insn_logged(this, pc, fetch);
@@ -292,7 +293,6 @@ void processor_t::step(size_t n)
         // Main simulation loop, fast path.
         for (auto ic_entry = _mmu->access_icache(pc); ; ) {
           auto fetch = ic_entry->data;
-          execute_insn_prehook(fetch.insn);
           pc = execute_insn_fast(this, pc, fetch);
           ic_entry = ic_entry->next;
           if (unlikely(ic_entry->tag != pc))
diff --git a/riscv/insns/c_jalr.h b/riscv/insns/c_jalr.h
index 12bc7f9..694f183 100644
--- a/riscv/insns/c_jalr.h
+++ b/riscv/insns/c_jalr.h
@@ -6,4 +6,5 @@ WRITE_REG(X_RA, tmp);
 
 if (ZICFILP_xLPE(STATE.v, STATE.prv)) {
   STATE.elp = ZICFILP_IS_LP_EXPECTED(insn.rvc_rs1());
+  serialize();
 }
diff --git a/riscv/insns/c_jr.h b/riscv/insns/c_jr.h
index c5162e9..af43dd3 100644
--- a/riscv/insns/c_jr.h
+++ b/riscv/insns/c_jr.h
@@ -4,4 +4,5 @@ set_pc(RVC_RS1 & ~reg_t(1));
 
 if (ZICFILP_xLPE(STATE.v, STATE.prv)) {
   STATE.elp = ZICFILP_IS_LP_EXPECTED(insn.rvc_rs1());
+  serialize();
 }
diff --git a/riscv/insns/jalr.h b/riscv/insns/jalr.h
index 0622a22..0606f67 100644
--- a/riscv/insns/jalr.h
+++ b/riscv/insns/jalr.h
@@ -4,4 +4,5 @@ WRITE_RD(tmp);
 
 if (ZICFILP_xLPE(STATE.v, STATE.prv)) {
   STATE.elp = ZICFILP_IS_LP_EXPECTED(insn.rs1());
+  serialize();
 }
diff --git a/riscv/processor.cc b/riscv/processor.cc
index 0564731..da49a37 100644
--- a/riscv/processor.cc
+++ b/riscv/processor.cc
@@ -94,14 +94,6 @@ processor_t::~processor_t()
   delete disassembler;
 }
 
-static void zicfilp_check_if_lpad_required(const elp_t elp, insn_t insn)
-{
-  if (unlikely(elp == elp_t::LP_EXPECTED)) {
-    // also see riscv/lpad.h for more checks performed
-    software_check((insn.bits() & MASK_LPAD) == MATCH_LPAD, LANDING_PAD_FAULT);
-  }
-}
-
 static void bad_option_string(const char *option, const char *value,
                               const char *msg)
 {
@@ -991,9 +983,13 @@ const char* processor_t::get_symbol(uint64_t addr)
   return sim->get_symbol(addr);
 }
 
-void processor_t::execute_insn_prehook(insn_t insn)
+void processor_t::check_if_lpad_required()
 {
-  zicfilp_check_if_lpad_required(state.elp, insn);
+  if (unlikely(state.elp == elp_t::LP_EXPECTED)) {
+    // also see insns/lpad.h for more checks performed
+    insn_fetch_t fetch = mmu->load_insn(state.pc);
+    software_check((fetch.insn.bits() & MASK_LPAD) == MATCH_LPAD, LANDING_PAD_FAULT);
+  }
 }
 
 void processor_t::disasm(insn_t insn)
diff --git a/riscv/processor.h b/riscv/processor.h
index f3e5294..3e37b43 100644
--- a/riscv/processor.h
+++ b/riscv/processor.h
@@ -319,7 +319,7 @@ public:
   void clear_waiting_for_interrupt() { in_wfi = false; };
   bool is_waiting_for_interrupt() { return in_wfi; };
 
-  void execute_insn_prehook(insn_t insn);
+  void check_if_lpad_required();
 
 private:
   const isa_parser_t * const isa;
-- 
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