From b8c6ccd50c61b7a2df5123ddc5a85ac7d089542b Mon Sep 17 00:00:00 2001
From: Mike Pall <mike>
Date: Sat, 9 Sep 2023 18:01:37 +0200
Subject: [PATCH] ARM64: Fix LDP/STP fusion (again).

Reported and analyzed by Zhongwei Yao. Fix by Peter Cawley. #1075
---
 src/lj_emit_arm64.h | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/lj_emit_arm64.h b/src/lj_emit_arm64.h
index d4c54255..9161c958 100644
--- a/src/lj_emit_arm64.h
+++ b/src/lj_emit_arm64.h
@@ -113,6 +113,17 @@ static int emit_checkofs(A64Ins ai, int64_t ofs)
   }
 }
 
+static LJ_AINLINE uint32_t emit_lso_pair_candidate(A64Ins ai, int ofs, int sc)
+{
+  if (ofs >= 0) {
+    return ai | A64F_U12(ofs>>sc);  /* Subsequent lj_ror checks ofs. */
+  } else if (ofs >= -256) {
+    return (ai^A64I_LS_U) | A64F_S9(ofs & 0x1ff);
+  } else {
+    return A64F_D(31);  /* Will mismatch prev. */
+  }
+}
+
 static void emit_lso(ASMState *as, A64Ins ai, Reg rd, Reg rn, int64_t ofs)
 {
   int ot = emit_checkofs(ai, ofs), sc = (ai >> 30) & 3;
@@ -124,11 +135,9 @@ static void emit_lso(ASMState *as, A64Ins ai, Reg rd, Reg rn, int64_t ofs)
     uint32_t prev = *as->mcp & ~A64F_D(31);
     int ofsm = ofs - (1<<sc), ofsp = ofs + (1<<sc);
     A64Ins aip;
-    if (prev == (ai | A64F_N(rn) | A64F_U12(ofsm>>sc)) ||
-	prev == ((ai^A64I_LS_U) | A64F_N(rn) | A64F_S9(ofsm&0x1ff))) {
+    if (prev == emit_lso_pair_candidate(ai | A64F_N(rn), ofsm, sc)) {
       aip = (A64F_A(rd) | A64F_D(*as->mcp & 31));
-    } else if (prev == (ai | A64F_N(rn) | A64F_U12(ofsp>>sc)) ||
-	       prev == ((ai^A64I_LS_U) | A64F_N(rn) | A64F_S9(ofsp&0x1ff))) {
+    } else if (prev == emit_lso_pair_candidate(ai | A64F_N(rn), ofsp, sc)) {
       aip = (A64F_D(rd) | A64F_A(*as->mcp & 31));
       ofsm = ofs;
     } else {