From 7f0c50304ace84794521d66d68f21827b7b58cad Mon Sep 17 00:00:00 2001
From: Scott Duensing <scott@duensing.com>
Date: Fri, 26 Jun 2026 21:00:32 -0500
Subject: [PATCH] Inadvertent bank-drop fixed.

---
 .../lib/Target/W65816/W65816AsmPrinter.cpp    | 43 ++++++++++++++-----
 1 file changed, 32 insertions(+), 11 deletions(-)

diff --git a/src/llvm/lib/Target/W65816/W65816AsmPrinter.cpp b/src/llvm/lib/Target/W65816/W65816AsmPrinter.cpp
index fc11f16..0540452 100644
--- a/src/llvm/lib/Target/W65816/W65816AsmPrinter.cpp
+++ b/src/llvm/lib/Target/W65816/W65816AsmPrinter.cpp
@@ -815,9 +815,17 @@ void W65816AsmPrinter::emitInstruction(const MachineInstr *MI) {
     IsLong = IsLong || isFarGlobalOperand(AddrMO);
     MCOperand Addr = lowerOperand(AddrMO, MCInstLowering);
     if (IsLong && Addr.isImm()) {
-      // 16-bit pointer sign-extended into i32 imm — mask back to 16 bits
-      // so the encoded bank byte is 0.  See STA8long for the rationale.
-      Addr = MCOperand::createImm(Addr.getImm() & 0xFFFFu);
+      // Sign-extended 16-bit pointer -> low 16 (bank 0); genuine 24-bit
+      // constant address -> keep low 24 (bank preserved).  See STA8long.
+      int64_t Imm = Addr.getImm();
+      int16_t Lo16 = static_cast<int16_t>(Imm);
+      bool IsSext16 =
+          (Imm == static_cast<int64_t>(Lo16)) ||
+          (static_cast<uint64_t>(Imm) ==
+           static_cast<uint64_t>(static_cast<uint32_t>(static_cast<int32_t>(Lo16))));
+      Addr = MCOperand::createImm(
+          IsSext16 ? (static_cast<uint64_t>(Imm) & 0xFFFFu)
+                   : (static_cast<uint64_t>(Imm) & 0xFFFFFFu));
     }
     emitSepM();
     EmitToStreamer(*OutStreamer,
@@ -878,15 +886,28 @@ void W65816AsmPrinter::emitInstruction(const MachineInstr *MI) {
       emitSepM();
     }
     MCOperand Addr = lowerOperand(MI->getOperand(1), MCInstLowering);
-    // STA_Long takes a 24-bit absolute address.  When the input is a
-    // const-int cast through a 16-bit pointer, TableGen sign-extends
-    // the 16-bit value into the i32 imm operand: 0xC035 (i16) becomes
-    // 0xFFFFC035 (i64).  Mask to 16 bits to recover the original
-    // pointer; the resulting encoding has bank=0 explicit.  Users who
-    // need a banked address should construct a far pointer rather than
-    // casting an int.
+    // STA_Long takes a 24-bit absolute address.  Two cases reach here as
+    // an immediate:
+    //  (a) a const-int cast through a 16-bit pointer, which TableGen
+    //      SIGN-EXTENDS into the wider imm (0xC035 -> ...FFFFC035); the
+    //      intended bank is 0, so recover the low 16 bits.
+    //  (b) a genuine >16-bit constant address such as 0xE12000 (a fixed
+    //      hardware register in bank $E1); this MUST keep its bank byte.
+    // Distinguish by the sign-extension round-trip: if the value equals
+    // the sign-extension of its low 16 bits it is case (a) -> low 16;
+    // otherwise it is case (b) -> keep the low 24 (bank included), dropping
+    // any above-bit-23 garbage.  The check tolerates both i32-in-i64 and
+    // full-i64 sign-extended representations of the immediate.
     if (IsLong && Addr.isImm()) {
-      Addr = MCOperand::createImm(Addr.getImm() & 0xFFFFu);
+      int64_t Imm = Addr.getImm();
+      int16_t Lo16 = static_cast<int16_t>(Imm);
+      bool IsSext16 =
+          (Imm == static_cast<int64_t>(Lo16)) ||
+          (static_cast<uint64_t>(Imm) ==
+           static_cast<uint64_t>(static_cast<uint32_t>(static_cast<int32_t>(Lo16))));
+      Addr = MCOperand::createImm(
+          IsSext16 ? (static_cast<uint64_t>(Imm) & 0xFFFFu)
+                   : (static_cast<uint64_t>(Imm) & 0xFFFFFFu));
     }
     EmitToStreamer(*OutStreamer,
         MCInstBuilder(IsLong ? W65816::STA_Long : W65816::STA_Abs)